Bicycle frame
Encyclopedia
A bicycle frame is the main component of a bicycle
, on to which wheel
s and other components are fitted. The modern and most common frame design for an upright bicycle is based on the safety bicycle
, and consists of two triangle
s, a main triangle and a paired rear triangle. This is known as the diamond frame.
The head tube contains the headset
, the interface with the fork
. The top tube connects the head tube to the seat tube at the top. The top tube may be positioned horizontally (parallel to the ground), or it may slope downwards towards the seat tube for additional stand-over clearance. The down tube connects the head tube to the bottom bracket
shell.
The rear triangle connects to the rear fork ends
, where the rear wheel is attached. It consists of the seat tube and paired chain stays and seat stays. The chain stays run parallel to the chain
, connecting the bottom bracket to the rear fork ends. The seat stays connect the top of the seat tube (often at or near the same point as the top tube) to the rear fork ends.
or dress
. The design has since been used in utility bikes to facilitate easy mounting and dismounting for both genders, and is also known as a step-through frame
. Another style that accomplishes similar results is the mixte.
, the lowrider bicycle
, and the wheelie bike
. In many cantilever frames the only straight tubes are the seat tube and the head tube.
moves the cranks to a position forward of the rider instead of underneath, generally improving the slipstream around the rider without the characteristic sharp bend at the waist used by racers of diamond-frame bicycles. Banned from bicycle racing in France in 1934 to avoid rendering diamond-frame bicycles obsolete in racing
, manufacturing of recumbents remained depressed for another half century, but many models from a range of manufactures were available by 2000.
. Examples include Humbers
, Pedersens
, and the one pictured.
frames are characterized by the ability to fold into a compact shape for transportation or storage.
frames are characterized by a large front wheel and a small rear wheel.
. In an integrated headset, cartridge bearings interface directly with the surface on the inside of the head tube, on non-integrated headsets the bearings (in a cartridge or not) interface with "cups" pressed into the head tube.
The top tube, or cross-bar, connects the top of the head tube to the top of the seat tube.
In a traditional-geometry diamond frame, the top tube is horizontal (parallel to the ground). In a compact-geometry frame, the top tube is normally sloped downward toward the seat tube for additional standover clearance. In a mountain bike
frame, the top tube is almost always sloped downward toward the seat tube. Radically sloped top tubes that compromise the integrity of the traditional diamond frame may require additional gusseting tubes, alternative frame construction, or different materials for equivalent strength. (See Road and triathlon bicycles for more information on geometries.)
Step-through frame
s usually have a top tube that slopes down steeply to allow the rider to mount and dismount the bicycle more easily. Alternative step-through designs may include leaving out the top tube out completely, as in monocoque
mainframe designs using a separated or hinged seat tube, and twin top tubes that continue to the rear fork ends as with the Mixte frame. These alternatives to the diamond frame provide greater versatility, though at the expense of added weight to achieve equivalent strength and rigidity.
Control cables are routed along mounts on the top tube, or sometimes inside the top tube. Most commonly, this includes the cable for the rear brake, but some mountain bikes and hybrid bicycle
s also route the front and rear derailleur cables along the top tube.
The space between the top tube and the rider's groin while straddling the bike and standing on the ground is called clearance. The total height from the ground to this point is called the height lever.
were mounted on the down tube. On newer ones, they are mounted with the brake levers on the handlebars.
Bottle cage
mounts are also on the down tube, usually on the top side, sometimes also on the bottom side. In addition to bottle cages, small air pumps may be fitted to these mounts as well.
of the bike, which connects to the saddle. The saddle height is adjustable by changing how far the seatpost is inserted into the seat tube. On some bikes, this is achieved using a quick release lever. The seatpost must be inserted at least a certain length; this is marked with a minimum insertion mark.
The seat tube also may have braze-on
mounts for a bottle cage
or front derailleur.
. When the rear derailleur cable is routed partially along the down tube, it is also routed along the chain stay. Occasionally (principally on frames made since the late 1990s) mountings for disc brakes will be attached to the chain stays. There may be a small brace that connects the chain stays in front of the rear wheel and behind the bottom bracket shell.
Chain stays may be designed using tapered or untapered tubing. They may be relieved, ovalized, crimped, S-shaped, or elevated to allow additional clearance for the rear wheel, chain, crankarms, or the heel of the foot.
The seat stays connect the top of the seat tube (often at or near the same point as the top tube) to the rear fork dropouts. A traditional frame uses a simple set of paralleled tubes connected by a bridge above the rear wheel.
Many alternatives to the traditional seat stay design have been introduced over the years. A style of seat stay that extends forward of the seat tube, below the rear end of the top tube and connects to the top tube in front of the seat tube, creating a small triangle, is called a Hellenic stay after the British frame builder Fred Hellens, who introduced them in 1923. Hellenic chainstays add aesthetic appeal at the expense of added weight.
Another common seatstay variant is the wishbone, single seat stay, or mono stay, which joins the stays together just above the rear wheel into a monotube that is joined to the seat tube. A wishbone design adds vertical rigidity without increasing lateral stiffness, generally an undesirable trait for bicycles with unsuspended rear wheels. The wishbone design is most appropriate when used as part of a rear triangle subframe on a bicycle with independent rear suspension.
A dual seat stay refers to seat stays which meet the front triangle of the bicycle at two separate points, usually side-by-side.
Fastback seat stays meet the seat tube at the back instead of the sides of the tube.
On most seat stays, a bridge or brace is typically used to connect the stays above the rear wheel and below the connection with the seat tube. Besides providing lateral rigidity, this bridge provides a mounting point for rear brakes, fenders, and racks. The seat stays themselves may also be fitted with brake mounts. Brake mounts are often absent from fixed-gear or track bike seat stays.
When the rear derailleur cable is routed partially along the top tube, it is also usually routed along the seat stay. One combination aluminum/carbon fiber racing frame design uses carbon fiber for the seat stays and aluminum for all other tubes. This takes advantage of the better vibration absorption of carbon fiber compared to aluminum.
. It is usually threaded, often left-hand threaded on the right (drive) side of the bike to prevent loosening by fretting induced precession
, and right-hand threaded on the left (non-drive) side. There are many variations, such as an eccentric
bottom bracket, which allows for adjustment in tension of the bicycle's chain. It is typically larger, unthreaded, and sometimes split. The chain stays, seat tube, and down tube all typically connect to the bottom bracket shell.
There are a few traditional standard shell widths (68, 70 or 73 mm). Road bikes usually use 68 mm; Italian road bikes use 70 mm; Early model mountain bikes use 73 mm; later models (1995 and newer) use 68 mm more commonly. Some modern bicycles have shell widths of 83 or 100 mm and these are for specialised downhill mountain biking or snowbiking applications. The shell width influences the Q factor
or tread of the bike. There are a few standard shell diameters (34.798 – 36 mm) with associated thread pitches (24 - 28 tpi).
The geometry of the frame depends on the intended use. For instance, a road bicycle
will place the handlebars in a lower and further position relative to the saddle giving a more crouched riding position; whereas a utility bicycle
emphasizes comfort and has higher handlebars resulting in an upright riding position.
Frame geometry also affects handling characteristics. For more information, see the Bicycle and motorcycle geometry
and the Bicycle and motorcycle dynamics
articles.
Frame size was traditionally measured from the center of the bottom bracket to the center of the top tube. Typical "medium" sizes are 54 or 56 cm (approximately 21.2 or 22 inches) for a European men's racing bicycle or 46 cm (about 18.5 inches) for a men's mountain bicycle. The wider range of frame geometries that are now made have given rise to different ways of measuring frame size; see the discussion by Sheldon Brown
. Touring frames tend to be longer, while racing frames are more compact.
Traditional geometry road frames are often associated with more comfort and greater stability, and tend to have a longer wheelbase which contributes to these two aspects. Compact geometry road frames have a lower center of gravity and tend to have a shorter wheelbase and smaller rear triangle, which give the bike quicker handling. Compact geometry also allows the top of the head tube to be above the top of the seat tube, decreasing standover height, and thus increasing standover clearance and lowering the center of gravity. Opinion is divided on the riding merits of the compact frame, but several manufacturers claim that a reduced range of sizes can fit most riders, and that it is easier to build a frame without a perfectly level top tube.
Road bicycles for racing tend to have a steeper seat tube angle, measured from the horizontal plane. This positions the rider aerodynamically and arguably in a stronger stroking position. The trade-off is comfort. Touring and comfort bicycles tend to have more slack seat tube angle traditionally. This positions the rider more on the sit bones and takes weight off the wrists, arms and neck, and, for men, improves circulation to the urinary and reproductive areas. With a slacker angle, designers lengthen the chainstay so that the center of gravity (that would otherwise be farther to the back over the wheel) is more ideally repositioned over the middle of the bike frame. The longer wheelbase contributes to effective shock absorption. In modern mass-manufactured touring and comfort bikes, the seat-tube angle is negligibly slacker, perhaps in order to reduce manufacturing costs by avoiding the need to reset welding jigs in automated processes, and thus do not provide the comfort of traditionally made or custom-made frames which do have noticeably slacker seat-tube angles.
Road racing bicycles
that are used in UCI-sanctioned races are governed by UCI
regulations, which state among other things that the frame must consist of two triangles. Hence designs that lack a seat tube or top tube are not allowed.
Triathlon
- or time-trial-specific frames rotate the rider forward around the axis of the bottom bracket of the bicycle as compared to the standard road bicycle frame. This is in order to put the rider in an even lower, more aerodynamic position. While handling and stability is reduced, these bicycles are designed to be ridden in environments with less group riding aspects. These frames tend to have steep seat-tube angles and low head tubes, and shorter wheelbase for the correct reach from the saddle to the handlebar. Additionally, since they are not governed by the UCI, some triathlon bicycles, such as the Zipp 2001
, Cheetah and Softride, have non-traditional frame layouts, which can produce better aerodynamics.
have much in common with road and time trial frames, but come with rear-facing, horizontal fork ends, rather than dropouts, to allow one to adjust the position of the rear wheel horizontally to set the proper chain tension. Also the seat tube angle is steeper than on road racing bikes.
s are often used; there are a number of variants, including full suspension models, which provide shock absorption for the front and rear wheels; and front suspension only models (hardtails) which deal only with shocks arising from the front wheel. The development of sophisticated suspension systems in the 1990s quickly resulted in many modifications to the classic diamond frame.
Recent mountain bicycles with rear suspension
systems have a pivoting rear triangle to actuate the rear shock absorber. There is much manufacturer variation in the frame design of full-suspension mountain bicycles, and different designs for different riding purposes.
traditionally have a fairly slack seat-tube and head-tube angle of about 66 or 67 degrees, which produces a very comfortable and upright "sit-up-and-beg" riding position. Other characteristics include a long wheelbase, upwards of 40 inches (often between 43 and 47 inches, or 57 inches for a longbike
), and a long fork rake, often of about 3 inches (76mm compared to 40mm for most road bicycles). This style of frame has had a resurgence in popularity in recent years due to its greater comfort compared to Mountain bicycles or Road bicycles. A variation on this type of bicycle is the "sports roadster" (also known as the "light roadster"), which typically has a lighter frame, and a slightly steeper seat-tube and head-tube angle of about 70 to 72 degrees.
The cycle types article describes additional variations.
It is also possible to add couplers
either during manufacturing or as a retrofit so that the frame can be disassembled into smaller pieces to facilitate packing and travel.
s. Frames can also be made from aluminum alloys, titanium, carbon fiber, and even bamboo
. Occasionally, diamond (shaped) frames have been formed from sections other than tubes. These include I-beam
s and monocoque
. Materials that have been used in these frames include wood
(solid or laminate
), magnesium
(cast I-beams), and thermoplastic
. Several properties of a material help decide whether it is appropriate in the construction of a bicycle frame:
Tube engineering and frame geometry can overcome much of the perceived shortcomings of these particular materials.
frames are often built using various types of steel alloys including chromoly. They are strong, easy to work, and relatively inexpensive, but denser (heavier) than many other structural materials. Steel tubing in traditional standard diameters is often less rigid than oversized tubing in other materials (due more to diameter than material); this flex allows for some shock absorption giving the rider a slightly less jarring ride compared to other more rigid tubings such as oversized aluminum. cf. www.sheldonbrown.com/frame-materials.html
A classic type of construction for both road bicycles and mountain bicycles uses standard cylindrical steel tubes which are connected with lugs. Lugs are fittings made of thicker pieces of steel. The tubes are fitted into the lugs, which encircle the end of the tube, and are then brazed
to the lug. Historically, the lower temperatures associated with brazing (silver brazing in particular) had less of a negative impact on the tubing strength than high temperature welding, allowing relatively light tube to be used without loss of strength. Recent advances in metallurgy
("air hardening") have created tubing that is not adversely affected, or whose properties are even improved by high temperature welding temperatures, which has allowed both TIG
& MIG
welding to sideline lugged construction in all but a few high end bicycles. More expensive lugged frame bicycles have lugs which are filed by hand into fancy shapes - both for weight savings and as a sign of craftsmanship. Unlike MIG or TIG welded frames, a lugged frame can be more easily repaired in the field due to its simple construction. Also, since steel tubing can rust (although in practice paint and anti-corrosion sprays can effectively prevent rust), the lugged frame allows a fast tube replacement with virtually no physical damage to the neighbouring tubes.
A more economical method of bicycle frame construction uses cylindrical steel tubing connected by TIG welding
, which does not require lugs to hold the tubes together. Instead, frame tubes are precisely aligned into a jig and fixed in place until the welding is complete. Fillet
brazing is another method of joining frame tubes without lugs. It is more labor intensive, and consequently is less likely to be used for production frames. As with TIG welding, Fillet frame tubes are precisely notched
or mitered
and then a fillet of brass is brazed onto the joint, similar to the lugged construction process. A fillet braze frame can achieve more aesthetic unity (smooth curved appearance) than a welded frame.
Among steel frames, using butted tubing
reduces weight and increases cost. Butting means that the wall thickness of the tubing changes from thick at the ends (for strength) to thinner in the middle (for lighter weight).
Cheaper steel bicycle frames are made of mild steel, such as might be used to manufacture automobiles or other common items. However, higher-quality bicycle frames are made of high strength steel alloys (generally chromium
-molybdenum
, or "chromoly" steel alloys) which can be made into lightweight tubing with very thin wall gauges. One of the most successful older steels was Reynolds
"531"
, a manganese
-molybdenum alloy steel. More common now is 4130 ChroMoly or similar alloys. Reynolds and Columbus
are two of the most famous manufacturers of bicycle tubing. A few medium-quality bicycles used these steel alloys for only some of the frame tubes. An example was the Schwinn Le tour (at least certain models), which used chromoly steel for the top and bottom tubes but used lower-quality steel for the rest of the frame.
A high-quality steel frame is lighter than a regular steel frame. This lightness makes it easier to ride uphill, and to accelerate on the flat. Also many riders feel thin-walled lightweight steel frames have a "liveliness" or "springiness" quality to their ride.
If the tubing label has been lost, a high-quality (chromoly or manganese) steel frame can be recognized by tapping it sharply with a flick of the fingernail. A high-quality frame will produce a bell-like ring where a regular-quality steel frame will produce a dull thunk. They can also be recognized by their weight (around 2.5 kg for frame and forks) and the type of lugs and fork ends used.
Aluminum alloy
s have a lower density and lower strength
compared with steel alloys, however, possess a better strength-to-weight ratio, giving them notable weight advantages over steel.
Early aluminum structures have shown to be more vulnerable to fatigue
, either due to ineffective alloys, or imperfect welding technique being used. This contrasts with some steel and titanium alloys, which have clear fatigue limit
s and are easier to weld or braze together. However, some of these disadvantages have since been partly negated, with more skilled labor capable of producing better quality welds, automation, and the greater accessibility of the same modern aluminum alloys as used in commercial airliners' structures, assuring strength and reliability comparable to steel frames. Aluminum's attractive strength to weight ratio as compared to steel, and certain mechanical properties, assure it a place among the favored frame-building materials (for example, a very strong rider, who does lots of hill-climbing, may prefer the stiffness of aluminum). Some disadvantages are that an aluminum frame does not have the same "feel" to an experienced cyclist as a steel frame, excessive ride harshness in lower quality frames, and decreased ease of reparability.
Popular alloys for bicycle frames are 6061 aluminum and 7005 aluminum.
The most popular type of construction today uses aluminum alloy tubes that are connected together by Tungsten Inert Gas (TIG) welding. Welded aluminum bicycle frames started to appear in the marketplace only after this type of welding became economical in the 1970s.
Aluminum has a different optimal wall thickness to tubing diameter than steel. It is at its strongest at around 200:1 (diameter:wall thickness), whereas steel is a small fraction of that. However, at this ratio, the wall thickness would be comparable to that of a beverage can, far too fragile against impacts. Thus, aluminum bicycle tubing is a compromise, offering a wall thickness to diameter ratio that is not of utmost efficiency, but gives us oversized tubing of more reasonable aerodynamically acceptable proportions and good resistance to impact. This results in a frame that is significantly stiffer than steel. While many riders claim that steel frames give a smoother ride than aluminum because aluminum frames are designed to be stiffer, that claim is of questionable validity: the bicycle frame itself is extremely stiff vertically because it is made of triangles, the sides of which do not change in length under stress. Conversely, this very argument calls the claim of aluminum frames having greater vertical stiffness into question. On the other hand, lateral and twisting (torsional) stiffness improves acceleration and handling in some circumstances.
Aluminum frames are generally recognized as having a lower weight than steel, although this is not always the case. An inexpensive aluminum frame may be heavier than an expensive steel frame. Butted aluminum tubes—where the wall thickness of the middle sections are made to be thinner than the end sections—are used by some manufacturers for weight savings. Non-round tubes are used for a variety of reasons, including stiffness, aerodynamics, and marketing. Various shapes focus on one or another of these goals, and seldom accomplish all.
is perhaps the most exotic and expensive metal commonly used for bicycle frame tubes. It combines many desirable characteristics, including a high strength to weight ratio and excellent corrosion resistance. Reasonable stiffness (roughly half that of steel) allow for many titanium frames to be constructed with "standard" tube sizes comparable to a traditional steel frame, although larger diameter tubing is becoming more common for more stiffness. As many titanium frames can be much more expensive than similar steel alloy frames, cost can put them out of reach for many cyclists. Many common titanium alloy
s and even specific tubes were originally developed for the aerospace
industry.
Titanium frame tubes are almost always joined by Gas Tungsten Arc Welding (GTAW or TIG) welding, although vacuum brazing
has been used on early frames. It is more difficult to machine than steel or aluminum, which sometimes limits its uses and also raises the effort (and cost) associated with this type of construction.
, a composite material
, is an increasingly popular non-metallic material commonly used for bicycle frames. Although expensive, it is light-weight, corrosion-resistant and strong, and can be formed into almost any shape desired. The result is a frame that can be fine-tuned for specific strength
where it is needed (to withstand pedaling forces), while allowing flexibility in other frame sections (for comfort). Custom carbon fiber bicycle frames may even be designed with individual tubes that are strong in one direction (such as laterally), while compliant in another direction (such as vertically). The ability to design an individual composite tube with properties that vary by orientation cannot be accomplished with any metal frame construction commonly in production.
Some carbon fiber frames use cylindrical tubes that are joined with adhesives and lugs, in a method somewhat analogous to a lugged steel frame. Another type of carbon fiber frames are manufactured in a single piece, called monocoque construction. While these composite materials provide light weight as well as high strength, they have much lower impact resistance and consequently are prone to damage if crashed or mishandled. It has also been suggested that these materials are vulnerable to fatigue failure, a process which occurs with use over a long period of time.
Many racing bicycles built for individual time trial
races and triathlon
s employ composite construction because the frame can be shaped with an aerodynamic profile not possible with cylindrical tubes, or would be excessively heavy in other materials. While this type of frame may in fact be heavier than others, its aerodynamic efficiency may help the cyclist to attain a higher overall speed.
Other materials besides carbon fiber, such as metallic boron
, can be added to the matrix to enhance stiffness further. Some newer high end frames are incorporating Kevlar fibers into the carbon weaves to improve vibration damping and impact strength, particularly in downtubes and seat- and chainstays.
Thermoplastic
s are a category of polymers that can be reheated and reshaped, and there are several ways that they can be used to create a bicycle frame. One implementation of thermoplastic bicycle frames are essentially carbon fiber frames with the fibers embedded in a thermoplastic material rather than the more common thermosetting epoxy
materials. GT Bicycles
was one of the first major manufacturers to produce a thermoplastic frame with their STS System frames in the mid 1990s. The carbon fibers were loosely woven into a tube along with fibers of thermoplastic. This tube was placed into a mould
with a bladder inside which was then inflated to force the carbon and plastic tube against the inside of the mould. The mould was then heated to melt the thermoplastic. Once the thermoplastic cooled it was removed from the mould in its final form.
which has around 64% the density of aluminum. In the 1980s, an engineer, Frank Kirk, devised a novel form of frame that was die cast in one piece and composed of I beams rather than tubes. A company, Kirk Precision Ltd, was established in Britain to manufacture both road bike and mountain bike frames with this technology. However, despite some early commercial success, there were problems with reliability and manufacture stopped in 1992.
The small number of modern magnesium frames in production are constructed conventionally using tubes.
Reportedly, a major problem with these frames is corrosion caused by the chemical reactivity of magnesium. Unless care is taken during assembly of the bicycle, there is likely to be galvanic corrosion at points where steel or aluminum components attach to the frame.
, usually referred to simply as scandium for marketing purposes although the Sc content is less than 0.5%. Scandium improves the welding characteristics of some aluminum alloys with superior fatigue resistance permitting the use of smaller diameter tubing, allowing for more frame design flexibility.
Carbon forks have become very common on racing bicycles of all frame materials.
has increased thickness near the joints for strength while keeping weight low with thinner material elsewhere. For example, triple butted means the tube, usually of an aluminum alloy, has three different thicknesses, with the thicker sections at the end where they are welded. The same material can be used in handle bars.
mounting holes, shifter
bosses, cable
stops, pump
pegs, cable guide
s, etc. -- are described as braze-ons because they were originally, and sometimes still are, brazed
on.
Bicycle
A bicycle, also known as a bike, pushbike or cycle, is a human-powered, pedal-driven, single-track vehicle, having two wheels attached to a frame, one behind the other. A person who rides a bicycle is called a cyclist, or bicyclist....
, on to which wheel
Bicycle wheel
A bicycle wheel is a wheel, most commonly a wire wheel, designed for bicycle. A pair is often called a wheelset, especially in the context of ready built "off the shelf" performance-oriented wheels....
s and other components are fitted. The modern and most common frame design for an upright bicycle is based on the safety bicycle
Safety bicycle
A safety bicycle is a type of bicycle that became very popular beginning in the late 1880s as an alternative to the penny-farthing or ordinary and is now the most common type of bicycle. Early bicycles of this style were known as safety bicycles because they were noted for, and marketed as, being...
, and consists of two triangle
Triangle
A triangle is one of the basic shapes of geometry: a polygon with three corners or vertices and three sides or edges which are line segments. A triangle with vertices A, B, and C is denoted ....
s, a main triangle and a paired rear triangle. This is known as the diamond frame.
Variations
Besides the ubiquitous diamond frame, many different frame types have been developed for the bicycle, several of which are still in common use today.Diamond
In the diamond frame, the main "triangle" is not actually a triangle because it consists of four tubes: the head tube, top tube, down tube and seat tube. The rear triangle consists of the seat tube joined by paired chain stays and seat stays.The head tube contains the headset
Headset (bicycle part)
The headset is the set of components on a bicycle that provides a rotatable interface between the bicycle fork and the head tube of the bicycle frame itself. The short tube through which the steerer of the fork passes is called the head tube. A typical headset consists of two cups that are pressed...
, the interface with the fork
Bicycle fork
A bicycle fork is the portion of a bicycle that holds the front wheel and allows the rider to steer and balance the bicycle. A fork consists of two fork ends which hold the front wheel axle, two blades which join at a fork crown, and a steerer or steering tube to which the handlebars attach ...
. The top tube connects the head tube to the seat tube at the top. The top tube may be positioned horizontally (parallel to the ground), or it may slope downwards towards the seat tube for additional stand-over clearance. The down tube connects the head tube to the bottom bracket
Bottom bracket
The bottom bracket on a bicycle connects the crankset to the bicycle and allows the crankset to rotate freely. It contains a spindle that the crankset attaches to, and the bearings that allow the spindle and cranks to rotate. The chainrings and pedals attach to the cranks...
shell.
The rear triangle connects to the rear fork ends
Dropout (bicycle part)
A bicycle dropout is a type of fork end that allows the rear wheel to be removed without first derailing the chain. The more inclusive term fork end refers to a slot in a frame or fork where the axle of the wheel is attached....
, where the rear wheel is attached. It consists of the seat tube and paired chain stays and seat stays. The chain stays run parallel to the chain
Bicycle chain
A bicycle chain is a roller chain that transfers power from the pedals to the drive-wheel of a bicycle, thus propelling it. Most bicycle chains are made from plain carbon or alloy steel, but some are nickel-plated to prevent rust, or simply for aesthetics. Nickel also confers a measure of...
, connecting the bottom bracket to the rear fork ends. The seat stays connect the top of the seat tube (often at or near the same point as the top tube) to the rear fork ends.
Step-through
Historically, women's bicycle frames had a top tube that connected in the middle of the seat tube instead of the top, resulting in a lower standover height. This was to allow the rider to dismount while wearing a skirtSkirt
A skirt is a tube- or cone-shaped garment that hangs from the waist and covers all or part of the legs.In the western world, skirts are usually considered women's clothing. However, there are exceptions...
or dress
Dress
A dress is a garment consisting of a skirt with an attached bodice or with a matching bodice giving the effect of a one-piece garment.Dress may also refer to:*Clothing in general*Costume, fancy dress...
. The design has since been used in utility bikes to facilitate easy mounting and dismounting for both genders, and is also known as a step-through frame
Step-through frame
A step-through frame is a type of bicycle frame, often used for utility bicycles, with a low or absent top tube or cross-bar....
. Another style that accomplishes similar results is the mixte.
Cantilever
In a cantilever bicycle frame the seat stays continue past the seat post and curve downwards to meet with the down tube. Cantilever frames are popular on the cruiser bicycleCruiser bicycle
Cruiser bicycles, also known as beach cruisers, combine balloon tires, upright seating posture, single-speed drivetrains, and straightforward steel construction with expressive styling...
, the lowrider bicycle
Lowrider bicycle
A lowrider bicycle is a highly customized bicycle with a long wheelbase and stylings inspired by lowrider cars. These bikes often feature a long, curved banana seat with a sissy bar and very tall upward-swept ape hanger handlebars...
, and the wheelie bike
Wheelie bike
A wheelie bike, also called a muscle bike, high-riser, or banana bike, is a type of stylized children's bicycle designed in the 1960s to resemble a chopper motorcycle and characterized by ape hanger handlebars, a banana seat with sissy bar, and small wheels. Notable examples include the Schwinn...
. In many cantilever frames the only straight tubes are the seat tube and the head tube.
Recumbent
The recumbent bicycleRecumbent bicycle
A recumbent bicycle is a bicycle that places the rider in a laid-back reclining position. Most recumbent riders choose this type of design for ergonomic reasons; the rider's weight is distributed comfortably over a larger area, supported by back and buttocks...
moves the cranks to a position forward of the rider instead of underneath, generally improving the slipstream around the rider without the characteristic sharp bend at the waist used by racers of diamond-frame bicycles. Banned from bicycle racing in France in 1934 to avoid rendering diamond-frame bicycles obsolete in racing
, manufacturing of recumbents remained depressed for another half century, but many models from a range of manufactures were available by 2000.
Prone
The uncommon prone bike moves the cranks to the rear of the rider, resulting in a head-forward, chest-down riding position.Cross or girder
A cross frame consists mainly to two tubes that form a cross: a seat tube from the bottom bracket to the saddle, and a backbone from the head tube to the rear hub.Truss
A truss frame uses additional tubes to form a trussTruss
In architecture and structural engineering, a truss is a structure comprising one or more triangular units constructed with straight members whose ends are connected at joints referred to as nodes. External forces and reactions to those forces are considered to act only at the nodes and result in...
. Examples include Humbers
Humber (bicycle)
Humber is an English brand of bicycle.One model is the Humber Sport 3-speed pictured on this page. It includes an unusual fork design, called "Duplex", in which each blade consist of two separate tubes, and a stylish chainring that includes the shape of five persons.-History:Made by Humber car...
, Pedersens
Pedersen bicycle
The Pedersen bicycle, also called the Dursley Pedersen bicycle is a bicycle that was developed by Danish inventor Mikael Pedersen and produced in the English town of Dursley. Though never hugely popular, they enjoy a devoted following and are still produced today...
, and the one pictured.
Folding
Folding bicycleFolding bicycle
A folding bicycle is a bicycle designed to fold into a compact form, facilitating transport and storage. When folded, the bikes can be more easily carried into buildings and workplaces or onto public transportation or more easily stored in compact living quarters or aboard a car, boat or plane...
frames are characterized by the ability to fold into a compact shape for transportation or storage.
Penny-farthing
Penny-farthingPenny-farthing
Penny-farthing, high wheel, high wheeler, and ordinary are all terms used to describe a type of bicycle with a large front wheel and a much smaller rear wheel that was popular after the boneshaker, until the development of the safety bicycle, in the 1880s...
frames are characterized by a large front wheel and a small rear wheel.
Others
- Frames without seat tubes, such as the TrekTrek Bicycle CorporationTrek Bicycle Corporation is a major bicycle and cycling product manufacturer and distributor under brand names Trek, Gary Fisher, Bontrager, Klein and until recently, LeMond Racing Cycles...
Y-Foil, the Zipp 2001Zipp 2001Zipp 2001 and 3001 were a line of bicycle frames, now discontinued, made by the Zipp company. While they have been out of production for 7 years, they are still considered one of the fastest time trial frames ever made, and still have a cult following within triathlon, where they remain...
, the KestrelKestrel USAKestrel is an American bicycle manufacturer headquartered in Santa Cruz, California specializing in high-end bikes for triathlon, road bicycle racing and mountain biking...
Airfoil, and most frames by SoftRide. - Frames without top tubes such as "Old Faithful" by Graeme ObreeGraeme ObreeGraeme Obree is a Scottish racing cyclist who twice broke the world hour record, in July 1993 and April 1994, and was the individual pursuit world champion in 1993 and 1995. He was known for his unusual riding positions and for the "Old Faithful" bicycle he built which included parts from a...
. - Frames that use cables for members that are only under tension, such as the Dursley Pedersen pictured.
- Frames with hoops replacing the seat tube, chain stays and seat stays: called "roundtail"s.
Frame tubes
The diamond frame consists of two triangles, a main triangle and a paired rear triangle. The main triangle consists of the head tube, top tube, down tube and seat tube. The rear triangle consists of the seat tube, and paired chain stays and seat stays.Head tube
The head tube contains the headset, the bearings for the fork via its steerer tubeBicycle fork
A bicycle fork is the portion of a bicycle that holds the front wheel and allows the rider to steer and balance the bicycle. A fork consists of two fork ends which hold the front wheel axle, two blades which join at a fork crown, and a steerer or steering tube to which the handlebars attach ...
. In an integrated headset, cartridge bearings interface directly with the surface on the inside of the head tube, on non-integrated headsets the bearings (in a cartridge or not) interface with "cups" pressed into the head tube.
Top tube
In a traditional-geometry diamond frame, the top tube is horizontal (parallel to the ground). In a compact-geometry frame, the top tube is normally sloped downward toward the seat tube for additional standover clearance. In a mountain bike
Mountain bike
A mountain bike or mountain bicycle is a bicycle created for off-road cycling. This activity includes traversing of rocks and washouts, and steep declines,...
frame, the top tube is almost always sloped downward toward the seat tube. Radically sloped top tubes that compromise the integrity of the traditional diamond frame may require additional gusseting tubes, alternative frame construction, or different materials for equivalent strength. (See Road and triathlon bicycles for more information on geometries.)
Step-through frame
Step-through frame
A step-through frame is a type of bicycle frame, often used for utility bicycles, with a low or absent top tube or cross-bar....
s usually have a top tube that slopes down steeply to allow the rider to mount and dismount the bicycle more easily. Alternative step-through designs may include leaving out the top tube out completely, as in monocoque
Monocoque
Monocoque is a construction technique that supports structural load by using an object's external skin, as opposed to using an internal frame or truss that is then covered with a non-load-bearing skin or coachwork...
mainframe designs using a separated or hinged seat tube, and twin top tubes that continue to the rear fork ends as with the Mixte frame. These alternatives to the diamond frame provide greater versatility, though at the expense of added weight to achieve equivalent strength and rigidity.
Control cables are routed along mounts on the top tube, or sometimes inside the top tube. Most commonly, this includes the cable for the rear brake, but some mountain bikes and hybrid bicycle
Hybrid bicycle
A hybrid bicycle is a bicycle designed for general-purpose utility and commuting on a wide variety of surfaces, including paved and unpaved roads, paths and trails...
s also route the front and rear derailleur cables along the top tube.
The space between the top tube and the rider's groin while straddling the bike and standing on the ground is called clearance. The total height from the ground to this point is called the height lever.
Down tube
The down tube connects the head tube to the bottom bracket shell. On racing bicycles and some mountain and hybrid bikes, the derailleur cables run along the down tube, or inside the down tube. On older racing bicycles, the shift leversShifter (bicycle part)
A bicycle shifter or gear control or gear levers is a component used to control the gearing mechanisms and select the desired gear ratio. Typically, they operate either a derailleur mechanism or an internal hub gear mechanism. In either case, the control is operated by moving a cable that connects...
were mounted on the down tube. On newer ones, they are mounted with the brake levers on the handlebars.
Bottle cage
Bottle cage
A bottle cage is device used to affix a water bottle to a bicycle. Composed of plastic, aluminum, stainless steel, titanium or carbon fiber, it is attached to the main frame of a bicycle, the handlebars, or behind the saddle...
mounts are also on the down tube, usually on the top side, sometimes also on the bottom side. In addition to bottle cages, small air pumps may be fitted to these mounts as well.
Seat tube
The seat tube contains the seatpostSeatpost
A bicycle seatpost, seatpin, saddlepole, saddle pillar, or saddle pin is a tube that extends upwards from the bicycle frame to the saddle. The amount that it extends out of the frame can usually be adjusted, and there is usually a mark that indicates the minimum insertion...
of the bike, which connects to the saddle. The saddle height is adjustable by changing how far the seatpost is inserted into the seat tube. On some bikes, this is achieved using a quick release lever. The seatpost must be inserted at least a certain length; this is marked with a minimum insertion mark.
The seat tube also may have braze-on
Braze-on
A braze-on is the name for any number of parts of a bicycle which have been permanently attached to the frame. The term "braze-on" comes from when these parts would have been brazed on to steel frame bicycles...
mounts for a bottle cage
Bottle cage
A bottle cage is device used to affix a water bottle to a bicycle. Composed of plastic, aluminum, stainless steel, titanium or carbon fiber, it is attached to the main frame of a bicycle, the handlebars, or behind the saddle...
or front derailleur.
Chain stays
The chain stays run parallel to the chain, connecting the bottom bracket shell to the rear fork endsDropout (bicycle part)
A bicycle dropout is a type of fork end that allows the rear wheel to be removed without first derailing the chain. The more inclusive term fork end refers to a slot in a frame or fork where the axle of the wheel is attached....
. When the rear derailleur cable is routed partially along the down tube, it is also routed along the chain stay. Occasionally (principally on frames made since the late 1990s) mountings for disc brakes will be attached to the chain stays. There may be a small brace that connects the chain stays in front of the rear wheel and behind the bottom bracket shell.
Chain stays may be designed using tapered or untapered tubing. They may be relieved, ovalized, crimped, S-shaped, or elevated to allow additional clearance for the rear wheel, chain, crankarms, or the heel of the foot.
Seat stays
Many alternatives to the traditional seat stay design have been introduced over the years. A style of seat stay that extends forward of the seat tube, below the rear end of the top tube and connects to the top tube in front of the seat tube, creating a small triangle, is called a Hellenic stay after the British frame builder Fred Hellens, who introduced them in 1923. Hellenic chainstays add aesthetic appeal at the expense of added weight.
Another common seatstay variant is the wishbone, single seat stay, or mono stay, which joins the stays together just above the rear wheel into a monotube that is joined to the seat tube. A wishbone design adds vertical rigidity without increasing lateral stiffness, generally an undesirable trait for bicycles with unsuspended rear wheels. The wishbone design is most appropriate when used as part of a rear triangle subframe on a bicycle with independent rear suspension.
A dual seat stay refers to seat stays which meet the front triangle of the bicycle at two separate points, usually side-by-side.
Fastback seat stays meet the seat tube at the back instead of the sides of the tube.
On most seat stays, a bridge or brace is typically used to connect the stays above the rear wheel and below the connection with the seat tube. Besides providing lateral rigidity, this bridge provides a mounting point for rear brakes, fenders, and racks. The seat stays themselves may also be fitted with brake mounts. Brake mounts are often absent from fixed-gear or track bike seat stays.
When the rear derailleur cable is routed partially along the top tube, it is also usually routed along the seat stay. One combination aluminum/carbon fiber racing frame design uses carbon fiber for the seat stays and aluminum for all other tubes. This takes advantage of the better vibration absorption of carbon fiber compared to aluminum.
Bottom bracket shell
The bottom bracket shell is a short and wide tube, relative to the other tubes in the frame, that runs side to side and holds the bottom bracketBottom bracket
The bottom bracket on a bicycle connects the crankset to the bicycle and allows the crankset to rotate freely. It contains a spindle that the crankset attaches to, and the bearings that allow the spindle and cranks to rotate. The chainrings and pedals attach to the cranks...
. It is usually threaded, often left-hand threaded on the right (drive) side of the bike to prevent loosening by fretting induced precession
Precession (mechanical)
Precession is the process of a round part in a round hole rotating with respect to that hole because of clearance between them and a radial force on the part that changes direction. The direction of rotation of the inner part is opposite to the direction of rotation of the radial force. Fretting...
, and right-hand threaded on the left (non-drive) side. There are many variations, such as an eccentric
Eccentric (mechanism)
In mechanical engineering, an eccentric is a circular disk solidly fixed to a rotating axle with its centre offset from that of the axle ....
bottom bracket, which allows for adjustment in tension of the bicycle's chain. It is typically larger, unthreaded, and sometimes split. The chain stays, seat tube, and down tube all typically connect to the bottom bracket shell.
There are a few traditional standard shell widths (68, 70 or 73 mm). Road bikes usually use 68 mm; Italian road bikes use 70 mm; Early model mountain bikes use 73 mm; later models (1995 and newer) use 68 mm more commonly. Some modern bicycles have shell widths of 83 or 100 mm and these are for specialised downhill mountain biking or snowbiking applications. The shell width influences the Q factor
Q Factor (Bicycles)
The Q Factor of a bicycle is the distance between the pedal attachment points on the crank arms, when measured parallel to the bottom bracket axle. It may also be referred to as the "tread" of the crankset. The term was coined by Grant Petersen during his time at Bridgestone Bicycles.Q Factor is...
or tread of the bike. There are a few standard shell diameters (34.798 – 36 mm) with associated thread pitches (24 - 28 tpi).
Frame geometry
The length of the tubes, and the angles at which they are attached define a frame geometry. In comparing different frame geometries, designers often compare the seat tube angle, head tube angle, (virtual) top tube length, and seat tube length. To complete the specification of a bicycle for use, the rider adjusts the relative positions of the saddle, pedals and handlebars:- saddle height, the distance from the center of the bottom bracket to the point of reference on top of the middle of the saddle.
- reach, the distance from the saddle to the handlebar.
- drop, the vertical distance between the reference at the top of the saddle to the handlebar.
- setback, the horizontal distance between the front of the saddle and the center of the bottom bracket.
- standover height, the height of the top tube above the ground.
- toe overlap, the amount that the feet can interfere with steering the front wheel.
The geometry of the frame depends on the intended use. For instance, a road bicycle
Road bicycle
The term road bicycle is used to describe bicycles built for traveling at speed on paved roads. Some sources use the term to mean racing bicycle...
will place the handlebars in a lower and further position relative to the saddle giving a more crouched riding position; whereas a utility bicycle
Utility bicycle
A utility bicycle is a bicycle designed for practical transportation, as opposed to bicycles which are primarily designed for recreation and competition, such as touring bicycles, racing bicycles, sport/training bicycles, and mountain bicycles. The vast majority of bicycles can be found in the...
emphasizes comfort and has higher handlebars resulting in an upright riding position.
Frame geometry also affects handling characteristics. For more information, see the Bicycle and motorcycle geometry
Bicycle and motorcycle geometry
Bicycle and motorcycle geometry is the collection of key measurements that define a particular bike configuration. Primary among these are wheelbase, steering axis angle, fork offset, and trail...
and the Bicycle and motorcycle dynamics
Bicycle and motorcycle dynamics
Bicycle and motorcycle dynamics is the science of the motion of bicycles and motorcycles and their components, due to the forces acting on them. Dynamics is a branch of classical mechanics, which in turn is a branch of physics. Bike motions of interest include balancing, steering, braking,...
articles.
Frame size
Sheldon Brown (bicycle mechanic)
Sheldon Brown was an American bicycle mechanic and technical authority on bicycles. He contributed to numerous print and online sources related to bicycling, bicycle mechanics and maintenance, including his own website — and received numerous awards for his contributions.-Biography:Brown...
. Touring frames tend to be longer, while racing frames are more compact.
Road and triathlon bicycles
A road racing bicycle is designed for efficient power transfer at minimum weight and drag. Broadly speaking, the road bicycle geometry is categorized as either a traditional geometry with a horizontal top tube, or a compact geometry with a sloping top tube.Traditional geometry road frames are often associated with more comfort and greater stability, and tend to have a longer wheelbase which contributes to these two aspects. Compact geometry road frames have a lower center of gravity and tend to have a shorter wheelbase and smaller rear triangle, which give the bike quicker handling. Compact geometry also allows the top of the head tube to be above the top of the seat tube, decreasing standover height, and thus increasing standover clearance and lowering the center of gravity. Opinion is divided on the riding merits of the compact frame, but several manufacturers claim that a reduced range of sizes can fit most riders, and that it is easier to build a frame without a perfectly level top tube.
Road bicycles for racing tend to have a steeper seat tube angle, measured from the horizontal plane. This positions the rider aerodynamically and arguably in a stronger stroking position. The trade-off is comfort. Touring and comfort bicycles tend to have more slack seat tube angle traditionally. This positions the rider more on the sit bones and takes weight off the wrists, arms and neck, and, for men, improves circulation to the urinary and reproductive areas. With a slacker angle, designers lengthen the chainstay so that the center of gravity (that would otherwise be farther to the back over the wheel) is more ideally repositioned over the middle of the bike frame. The longer wheelbase contributes to effective shock absorption. In modern mass-manufactured touring and comfort bikes, the seat-tube angle is negligibly slacker, perhaps in order to reduce manufacturing costs by avoiding the need to reset welding jigs in automated processes, and thus do not provide the comfort of traditionally made or custom-made frames which do have noticeably slacker seat-tube angles.
Road racing bicycles
Racing bicycle
A racing bicycle, also known as a road bike, is a bicycle designed for competitive road cycling, a sport governed by according to the rules of the Union Cycliste Internationale...
that are used in UCI-sanctioned races are governed by UCI
Union Cycliste Internationale
Union Cycliste Internationale is the world governing body for sports cycling and oversees international competitive cycling events. The UCI is based in Aigle, Switzerland....
regulations, which state among other things that the frame must consist of two triangles. Hence designs that lack a seat tube or top tube are not allowed.
Triathlon
A triathlon is a multi-sport event involving the completion of three continuous and sequential endurance events. While many variations of the sport exist, triathlon, in its most popular form, involves swimming, cycling, and running in immediate succession over various distances...
- or time-trial-specific frames rotate the rider forward around the axis of the bottom bracket of the bicycle as compared to the standard road bicycle frame. This is in order to put the rider in an even lower, more aerodynamic position. While handling and stability is reduced, these bicycles are designed to be ridden in environments with less group riding aspects. These frames tend to have steep seat-tube angles and low head tubes, and shorter wheelbase for the correct reach from the saddle to the handlebar. Additionally, since they are not governed by the UCI, some triathlon bicycles, such as the Zipp 2001
Zipp 2001
Zipp 2001 and 3001 were a line of bicycle frames, now discontinued, made by the Zipp company. While they have been out of production for 7 years, they are still considered one of the fastest time trial frames ever made, and still have a cult following within triathlon, where they remain...
, Cheetah and Softride, have non-traditional frame layouts, which can produce better aerodynamics.
Track bicycles
Track framesTrack bicycle
A track bicycle or track bike is a bicycle optimized for racing at a velodrome or outdoor track. Unlike road bicycles, the track bike is a fixed-gear bicycle and so has a single gear and neither freewheel nor brakes. Tires are narrow and inflated to high pressure to reduce rolling resistance...
have much in common with road and time trial frames, but come with rear-facing, horizontal fork ends, rather than dropouts, to allow one to adjust the position of the rear wheel horizontally to set the proper chain tension. Also the seat tube angle is steeper than on road racing bikes.
Mountain bicycles
For ride comfort and better handling, shock absorberShock absorber
A shock absorber is a mechanical device designed to smooth out or damp shock impulse, and dissipate kinetic energy. It is a type of dashpot.-Nomenclature:...
s are often used; there are a number of variants, including full suspension models, which provide shock absorption for the front and rear wheels; and front suspension only models (hardtails) which deal only with shocks arising from the front wheel. The development of sophisticated suspension systems in the 1990s quickly resulted in many modifications to the classic diamond frame.
Recent mountain bicycles with rear suspension
Suspension (vehicle)
Suspension is the term given to the system of springs, shock absorbers and linkages that connects a vehicle to its wheels. Suspension systems serve a dual purpose — contributing to the car's roadholding/handling and braking for good active safety and driving pleasure, and keeping vehicle occupants...
systems have a pivoting rear triangle to actuate the rear shock absorber. There is much manufacturer variation in the frame design of full-suspension mountain bicycles, and different designs for different riding purposes.
Roadster/utility bicycles
Roadster bicyclesRoadster (bicycle)
A roadster, aka English roadster, is a type of utility bicycle once common in Britain and still very common in Asia, Africa, Denmark and the Netherlands, however, during the past several years, traditionally styled roadster bicycles have gained considerable popularity in the United States and...
traditionally have a fairly slack seat-tube and head-tube angle of about 66 or 67 degrees, which produces a very comfortable and upright "sit-up-and-beg" riding position. Other characteristics include a long wheelbase, upwards of 40 inches (often between 43 and 47 inches, or 57 inches for a longbike
Longtail (bicycle)
Longtail is a type of bicycle with a longer than usual frame wheelbase at the rear compared to a standard utility bicycle...
), and a long fork rake, often of about 3 inches (76mm compared to 40mm for most road bicycles). This style of frame has had a resurgence in popularity in recent years due to its greater comfort compared to Mountain bicycles or Road bicycles. A variation on this type of bicycle is the "sports roadster" (also known as the "light roadster"), which typically has a lighter frame, and a slightly steeper seat-tube and head-tube angle of about 70 to 72 degrees.
Diamond frame variations
There are many variations on the basic diamond frame design.- The elevated chainstay bicycle was popular in the early 90s. It featured a rear triangle with elevated bottom frame stays, negating the need for the chain to be drawn through the rear frame. This allowed for a shorter wheelbase and improved handling during technical ascents, at the cost of compromised integrity and resultant increased bottom bracket flex (unless reinforced) compared to a frame with traditional chainstays.
The cycle types article describes additional variations.
It is also possible to add couplers
Bicycle Torque Coupling
An S and S Coupling also known as a Bicycle Torque Coupling or BTC is a coupling which enables bicycle frames to be separated into smaller pieces, usually to facilitate packing and transporting. They can be built into the frame by the frame manufacturer when the frame is originally assembled or...
either during manufacturing or as a retrofit so that the frame can be disassembled into smaller pieces to facilitate packing and travel.
Frame materials
Historically, the most common material for the tubes of a bicycle frame has been steel. Steel frames can be very inexpensive carbon steel to highly specialised using high performance alloyAlloy
An alloy is a mixture or metallic solid solution composed of two or more elements. Complete solid solution alloys give single solid phase microstructure, while partial solutions give two or more phases that may or may not be homogeneous in distribution, depending on thermal history...
s. Frames can also be made from aluminum alloys, titanium, carbon fiber, and even bamboo
Bamboo
Bamboo is a group of perennial evergreens in the true grass family Poaceae, subfamily Bambusoideae, tribe Bambuseae. Giant bamboos are the largest members of the grass family....
. Occasionally, diamond (shaped) frames have been formed from sections other than tubes. These include I-beam
I-beam
-beams, also known as H-beams, W-beams , rolled steel joist , or double-T are beams with an - or H-shaped cross-section. The horizontal elements of the "" are flanges, while the vertical element is the web...
s and monocoque
Monocoque
Monocoque is a construction technique that supports structural load by using an object's external skin, as opposed to using an internal frame or truss that is then covered with a non-load-bearing skin or coachwork...
. Materials that have been used in these frames include wood
Wood
Wood is a hard, fibrous tissue found in many trees. It has been used for hundreds of thousands of years for both fuel and as a construction material. It is an organic material, a natural composite of cellulose fibers embedded in a matrix of lignin which resists compression...
(solid or laminate
Laminate
A laminate is a material that can be constructed by uniting two or more layers of material together. The process of creating a laminate is lamination, which in common parlance refers to the placing of something between layers of plastic and gluing them with heat and/or pressure, usually with an...
), magnesium
Magnesium
Magnesium is a chemical element with the symbol Mg, atomic number 12, and common oxidation number +2. It is an alkaline earth metal and the eighth most abundant element in the Earth's crust and ninth in the known universe as a whole...
(cast I-beams), and thermoplastic
Thermoplastic
Thermoplastic, also known as a thermosoftening plastic, is a polymer that turns to a liquid when heated and freezes to a very glassy state when cooled sufficiently...
. Several properties of a material help decide whether it is appropriate in the construction of a bicycle frame:
- DensityDensityThe mass density or density of a material is defined as its mass per unit volume. The symbol most often used for density is ρ . In some cases , density is also defined as its weight per unit volume; although, this quantity is more properly called specific weight...
(or specific gravitySpecific gravitySpecific gravity is the ratio of the density of a substance to the density of a reference substance. Apparent specific gravity is the ratio of the weight of a volume of the substance to the weight of an equal volume of the reference substance. The reference substance is nearly always water for...
) is a measure of how light or heavy the material per unit volume. - StiffnessStiffnessStiffness is the resistance of an elastic body to deformation by an applied force along a given degree of freedom when a set of loading points and boundary conditions are prescribed on the elastic body.-Calculations:...
(or elastic modulusElastic modulusAn elastic modulus, or modulus of elasticity, is the mathematical description of an object or substance's tendency to be deformed elastically when a force is applied to it...
) can in theory affect the ride comfort and power transmission efficiency. In practice, because even a very flexible frame is much more stiff than the tires and saddle, ride comfort is in the end more a factor of saddle choice, frame geometry, tire choice, and bicycle fit. Lateral stiffness is far more difficult to achieve because of the narrow profile of a frame, and too much flexibility can affect power transmission, primarily through tire scrub on the road due to rear triangle distortion, brakes rubbing on the rims and the chain rubbing on gear mechanisms. In extreme cases gears can change themselves when the rider applies high torque out of the saddle. - Yield strengthTensile strengthUltimate tensile strength , often shortened to tensile strength or ultimate strength, is the maximum stress that a material can withstand while being stretched or pulled before necking, which is when the specimen's cross-section starts to significantly contract...
determines how much force is needed to permanently deform the material (for crash-worthiness). - Elongation determines how much deformity the material allows before cracking (for crash-worthiness).
- Fatigue limit and Endurance limitFatigue (material)'In materials science, fatigue is the progressive and localized structural damage that occurs when a material is subjected to cyclic loading. The nominal maximum stress values are less than the ultimate tensile stress limit, and may be below the yield stress limit of the material.Fatigue occurs...
determines the durability of the frame when subjected to cyclical stress from pedaling or ride bumps.
Tube engineering and frame geometry can overcome much of the perceived shortcomings of these particular materials.
Steel
SteelSteel
Steel is an alloy that consists mostly of iron and has a carbon content between 0.2% and 2.1% by weight, depending on the grade. Carbon is the most common alloying material for iron, but various other alloying elements are used, such as manganese, chromium, vanadium, and tungsten...
frames are often built using various types of steel alloys including chromoly. They are strong, easy to work, and relatively inexpensive, but denser (heavier) than many other structural materials. Steel tubing in traditional standard diameters is often less rigid than oversized tubing in other materials (due more to diameter than material); this flex allows for some shock absorption giving the rider a slightly less jarring ride compared to other more rigid tubings such as oversized aluminum. cf. www.sheldonbrown.com/frame-materials.html
A classic type of construction for both road bicycles and mountain bicycles uses standard cylindrical steel tubes which are connected with lugs. Lugs are fittings made of thicker pieces of steel. The tubes are fitted into the lugs, which encircle the end of the tube, and are then brazed
Brazing
Brazing is a metal-joining process whereby a filler metal is heated above and distributed between two or more close-fitting parts by capillary action. The filler metal is brought slightly above its melting temperature while protected by a suitable atmosphere, usually a flux...
to the lug. Historically, the lower temperatures associated with brazing (silver brazing in particular) had less of a negative impact on the tubing strength than high temperature welding, allowing relatively light tube to be used without loss of strength. Recent advances in metallurgy
Metallurgy
Metallurgy is a domain of materials science that studies the physical and chemical behavior of metallic elements, their intermetallic compounds, and their mixtures, which are called alloys. It is also the technology of metals: the way in which science is applied to their practical use...
("air hardening") have created tubing that is not adversely affected, or whose properties are even improved by high temperature welding temperatures, which has allowed both TIG
Tig
Tig may refer to:*Tig Notaro, an American stand-up comic*Tig, another name for tag *Alex "Tig" Trager, a character in Sons of AnarchyTIG may refer to:*Tungsten inert gas welding, aka gas tungsten arc welding...
& MIG
Gas metal arc welding
Gas metal arc welding , sometimes referred to by its subtypes metal inert gas welding or metal active gas welding, is a semi-automatic or automatic arc welding process in which a continuous and consumable wire electrode and a shielding gas are fed through a welding gun...
welding to sideline lugged construction in all but a few high end bicycles. More expensive lugged frame bicycles have lugs which are filed by hand into fancy shapes - both for weight savings and as a sign of craftsmanship. Unlike MIG or TIG welded frames, a lugged frame can be more easily repaired in the field due to its simple construction. Also, since steel tubing can rust (although in practice paint and anti-corrosion sprays can effectively prevent rust), the lugged frame allows a fast tube replacement with virtually no physical damage to the neighbouring tubes.
A more economical method of bicycle frame construction uses cylindrical steel tubing connected by TIG welding
Welding
Welding is a fabrication or sculptural process that joins materials, usually metals or thermoplastics, by causing coalescence. This is often done by melting the workpieces and adding a filler material to form a pool of molten material that cools to become a strong joint, with pressure sometimes...
, which does not require lugs to hold the tubes together. Instead, frame tubes are precisely aligned into a jig and fixed in place until the welding is complete. Fillet
Fillet (mechanics)
In mechanical engineering, a fillet is a concave easing of an interior corner of a part design. A rounding of an exterior corner is called a "round" or a "chamfer".-Applications:...
brazing is another method of joining frame tubes without lugs. It is more labor intensive, and consequently is less likely to be used for production frames. As with TIG welding, Fillet frame tubes are precisely notched
Notching
Notching is a metal-cutting process used on sheetmetal or thin barstock, sometimes on angle sections or tube. A shearing or punching process is used in a press, so as to cut vertically down and perpendicular to the surface, working from the edge of a workpiece...
or mitered
Miter joint
A miter joint , sometimes shortened to miter, is a joint made by bevelling each of two parts to be joined, usually at a 45° angle, to form a corner, usually a 90° angle...
and then a fillet of brass is brazed onto the joint, similar to the lugged construction process. A fillet braze frame can achieve more aesthetic unity (smooth curved appearance) than a welded frame.
Among steel frames, using butted tubing
Butted tubing
Butted tubing is a bicycle construction design component. It is used to increase the thickness at the joints of the frame while allowing thinner metal or polymer everywhere else...
reduces weight and increases cost. Butting means that the wall thickness of the tubing changes from thick at the ends (for strength) to thinner in the middle (for lighter weight).
Cheaper steel bicycle frames are made of mild steel, such as might be used to manufacture automobiles or other common items. However, higher-quality bicycle frames are made of high strength steel alloys (generally chromium
Chromium
Chromium is a chemical element which has the symbol Cr and atomic number 24. It is the first element in Group 6. It is a steely-gray, lustrous, hard metal that takes a high polish and has a high melting point. It is also odorless, tasteless, and malleable...
-molybdenum
Molybdenum
Molybdenum , is a Group 6 chemical element with the symbol Mo and atomic number 42. The name is from Neo-Latin Molybdaenum, from Ancient Greek , meaning lead, itself proposed as a loanword from Anatolian Luvian and Lydian languages, since its ores were confused with lead ores...
, or "chromoly" steel alloys) which can be made into lightweight tubing with very thin wall gauges. One of the most successful older steels was Reynolds
Reynolds Cycle Technology
Reynolds Cycle Technology is a manufacturer of tubing for bicycle frames and other bicycle components based in Birmingham, England established in 1898.-History:...
"531"
Reynolds 531
Reynolds 531 is a brand name, registered to Reynolds Cycle Technology of Birmingham in the United Kingdom, for a manganese-molybdenum, medium carbon steel bicycle tubing....
, a manganese
Manganese
Manganese is a chemical element, designated by the symbol Mn. It has the atomic number 25. It is found as a free element in nature , and in many minerals...
-molybdenum alloy steel. More common now is 4130 ChroMoly or similar alloys. Reynolds and Columbus
Columbus Tubing
Columbus is a manufacturer of steel tubing used in bicycle frames, located in Settala, in the Province of Milan. The company was founded in 1919 by A.L. Columbo and was taken over by Columbo's youngest son, Antonio, in 1977...
are two of the most famous manufacturers of bicycle tubing. A few medium-quality bicycles used these steel alloys for only some of the frame tubes. An example was the Schwinn Le tour (at least certain models), which used chromoly steel for the top and bottom tubes but used lower-quality steel for the rest of the frame.
A high-quality steel frame is lighter than a regular steel frame. This lightness makes it easier to ride uphill, and to accelerate on the flat. Also many riders feel thin-walled lightweight steel frames have a "liveliness" or "springiness" quality to their ride.
If the tubing label has been lost, a high-quality (chromoly or manganese) steel frame can be recognized by tapping it sharply with a flick of the fingernail. A high-quality frame will produce a bell-like ring where a regular-quality steel frame will produce a dull thunk. They can also be recognized by their weight (around 2.5 kg for frame and forks) and the type of lugs and fork ends used.
Aluminum alloys
Aluminium alloy
Aluminium alloys are alloys in which aluminium is the predominant metal. The typical alloying elements are copper, magnesium, manganese, silicon and zinc. There are two principal classifications, namely casting alloys and wrought alloys, both of which are further subdivided into the categories...
s have a lower density and lower strength
Strength of materials
In materials science, the strength of a material is its ability to withstand an applied stress without failure. The applied stress may be tensile, compressive, or shear. Strength of materials is a subject which deals with loads, deformations and the forces acting on a material. A load applied to a...
compared with steel alloys, however, possess a better strength-to-weight ratio, giving them notable weight advantages over steel.
Early aluminum structures have shown to be more vulnerable to fatigue
Fatigue (material)
'In materials science, fatigue is the progressive and localized structural damage that occurs when a material is subjected to cyclic loading. The nominal maximum stress values are less than the ultimate tensile stress limit, and may be below the yield stress limit of the material.Fatigue occurs...
, either due to ineffective alloys, or imperfect welding technique being used. This contrasts with some steel and titanium alloys, which have clear fatigue limit
Fatigue limit
Fatigue limit, endurance limit, and fatigue strength are all expressions used to describe a property of materials: the amplitude of cyclic stress that can be applied to the material without causing fatigue failure. Ferrous alloys and titanium alloys have a distinct limit, an amplitude below which...
s and are easier to weld or braze together. However, some of these disadvantages have since been partly negated, with more skilled labor capable of producing better quality welds, automation, and the greater accessibility of the same modern aluminum alloys as used in commercial airliners' structures, assuring strength and reliability comparable to steel frames. Aluminum's attractive strength to weight ratio as compared to steel, and certain mechanical properties, assure it a place among the favored frame-building materials (for example, a very strong rider, who does lots of hill-climbing, may prefer the stiffness of aluminum). Some disadvantages are that an aluminum frame does not have the same "feel" to an experienced cyclist as a steel frame, excessive ride harshness in lower quality frames, and decreased ease of reparability.
Popular alloys for bicycle frames are 6061 aluminum and 7005 aluminum.
The most popular type of construction today uses aluminum alloy tubes that are connected together by Tungsten Inert Gas (TIG) welding. Welded aluminum bicycle frames started to appear in the marketplace only after this type of welding became economical in the 1970s.
Aluminum has a different optimal wall thickness to tubing diameter than steel. It is at its strongest at around 200:1 (diameter:wall thickness), whereas steel is a small fraction of that. However, at this ratio, the wall thickness would be comparable to that of a beverage can, far too fragile against impacts. Thus, aluminum bicycle tubing is a compromise, offering a wall thickness to diameter ratio that is not of utmost efficiency, but gives us oversized tubing of more reasonable aerodynamically acceptable proportions and good resistance to impact. This results in a frame that is significantly stiffer than steel. While many riders claim that steel frames give a smoother ride than aluminum because aluminum frames are designed to be stiffer, that claim is of questionable validity: the bicycle frame itself is extremely stiff vertically because it is made of triangles, the sides of which do not change in length under stress. Conversely, this very argument calls the claim of aluminum frames having greater vertical stiffness into question. On the other hand, lateral and twisting (torsional) stiffness improves acceleration and handling in some circumstances.
Aluminum frames are generally recognized as having a lower weight than steel, although this is not always the case. An inexpensive aluminum frame may be heavier than an expensive steel frame. Butted aluminum tubes—where the wall thickness of the middle sections are made to be thinner than the end sections—are used by some manufacturers for weight savings. Non-round tubes are used for a variety of reasons, including stiffness, aerodynamics, and marketing. Various shapes focus on one or another of these goals, and seldom accomplish all.
Titanium
TitaniumTitanium
Titanium is a chemical element with the symbol Ti and atomic number 22. It has a low density and is a strong, lustrous, corrosion-resistant transition metal with a silver color....
is perhaps the most exotic and expensive metal commonly used for bicycle frame tubes. It combines many desirable characteristics, including a high strength to weight ratio and excellent corrosion resistance. Reasonable stiffness (roughly half that of steel) allow for many titanium frames to be constructed with "standard" tube sizes comparable to a traditional steel frame, although larger diameter tubing is becoming more common for more stiffness. As many titanium frames can be much more expensive than similar steel alloy frames, cost can put them out of reach for many cyclists. Many common titanium alloy
Titanium alloy
Titanium alloys are metallic materials which contain a mixture of titanium and other chemical elements. Such alloys have very high tensile strength and toughness , light weight, extraordinary corrosion resistance, and ability to withstand extreme temperatures...
s and even specific tubes were originally developed for the aerospace
Aerospace engineering
Aerospace engineering is the primary branch of engineering concerned with the design, construction and science of aircraft and spacecraft. It is divided into two major and overlapping branches: aeronautical engineering and astronautical engineering...
industry.
Titanium frame tubes are almost always joined by Gas Tungsten Arc Welding (GTAW or TIG) welding, although vacuum brazing
Brazing
Brazing is a metal-joining process whereby a filler metal is heated above and distributed between two or more close-fitting parts by capillary action. The filler metal is brought slightly above its melting temperature while protected by a suitable atmosphere, usually a flux...
has been used on early frames. It is more difficult to machine than steel or aluminum, which sometimes limits its uses and also raises the effort (and cost) associated with this type of construction.
Carbon fiber
Carbon fiberCarbon fiber
Carbon fiber, alternatively graphite fiber, carbon graphite or CF, is a material consisting of fibers about 5–10 μm in diameter and composed mostly of carbon atoms. The carbon atoms are bonded together in crystals that are more or less aligned parallel to the long axis of the fiber...
, a composite material
Composite material
Composite materials, often shortened to composites or called composition materials, are engineered or naturally occurring materials made from two or more constituent materials with significantly different physical or chemical properties which remain separate and distinct at the macroscopic or...
, is an increasingly popular non-metallic material commonly used for bicycle frames. Although expensive, it is light-weight, corrosion-resistant and strong, and can be formed into almost any shape desired. The result is a frame that can be fine-tuned for specific strength
Specific strength
The specific strength is a material's strength divided by its density. It is also known as the strength-to-weight ratio or strength/weight ratio. In fiber or textile applications, tenacity is the usual measure of specific strength...
where it is needed (to withstand pedaling forces), while allowing flexibility in other frame sections (for comfort). Custom carbon fiber bicycle frames may even be designed with individual tubes that are strong in one direction (such as laterally), while compliant in another direction (such as vertically). The ability to design an individual composite tube with properties that vary by orientation cannot be accomplished with any metal frame construction commonly in production.
Some carbon fiber frames use cylindrical tubes that are joined with adhesives and lugs, in a method somewhat analogous to a lugged steel frame. Another type of carbon fiber frames are manufactured in a single piece, called monocoque construction. While these composite materials provide light weight as well as high strength, they have much lower impact resistance and consequently are prone to damage if crashed or mishandled. It has also been suggested that these materials are vulnerable to fatigue failure, a process which occurs with use over a long period of time.
Many racing bicycles built for individual time trial
Individual time trial
An individual time trial is a road bicycle race in which cyclists race alone against the clock . There are also track-based time trials where riders compete in velodromes, and team time trials...
races and triathlon
Triathlon
A triathlon is a multi-sport event involving the completion of three continuous and sequential endurance events. While many variations of the sport exist, triathlon, in its most popular form, involves swimming, cycling, and running in immediate succession over various distances...
s employ composite construction because the frame can be shaped with an aerodynamic profile not possible with cylindrical tubes, or would be excessively heavy in other materials. While this type of frame may in fact be heavier than others, its aerodynamic efficiency may help the cyclist to attain a higher overall speed.
Other materials besides carbon fiber, such as metallic boron
Boron
Boron is the chemical element with atomic number 5 and the chemical symbol B. Boron is a metalloid. Because boron is not produced by stellar nucleosynthesis, it is a low-abundance element in both the solar system and the Earth's crust. However, boron is concentrated on Earth by the...
, can be added to the matrix to enhance stiffness further. Some newer high end frames are incorporating Kevlar fibers into the carbon weaves to improve vibration damping and impact strength, particularly in downtubes and seat- and chainstays.
Thermoplastic
Thermoplastic
Thermoplastic, also known as a thermosoftening plastic, is a polymer that turns to a liquid when heated and freezes to a very glassy state when cooled sufficiently...
s are a category of polymers that can be reheated and reshaped, and there are several ways that they can be used to create a bicycle frame. One implementation of thermoplastic bicycle frames are essentially carbon fiber frames with the fibers embedded in a thermoplastic material rather than the more common thermosetting epoxy
Epoxy
Epoxy, also known as polyepoxide, is a thermosetting polymer formed from reaction of an epoxide "resin" with polyamine "hardener". Epoxy has a wide range of applications, including fiber-reinforced plastic materials and general purpose adhesives....
materials. GT Bicycles
GT Bicycles
GT Bicycles is a large American manufacturer of road, mountain, and bmxbicycles. The company was founded in 1979 by Gary Turner, a welding engineer and Richard Long, a bike shop owner. The company merged with Schwinn in 1998, but the conglomerate went bankrupt in 2001, and was acquired by Pacific...
was one of the first major manufacturers to produce a thermoplastic frame with their STS System frames in the mid 1990s. The carbon fibers were loosely woven into a tube along with fibers of thermoplastic. This tube was placed into a mould
Molding (process)
Molding or moulding is the process of manufacturing by shaping pliable raw material using a rigid frame or model called a pattern....
with a bladder inside which was then inflated to force the carbon and plastic tube against the inside of the mould. The mould was then heated to melt the thermoplastic. Once the thermoplastic cooled it was removed from the mould in its final form.
Magnesium
A handful of bicycle frames are made from magnesiumMagnesium
Magnesium is a chemical element with the symbol Mg, atomic number 12, and common oxidation number +2. It is an alkaline earth metal and the eighth most abundant element in the Earth's crust and ninth in the known universe as a whole...
which has around 64% the density of aluminum. In the 1980s, an engineer, Frank Kirk, devised a novel form of frame that was die cast in one piece and composed of I beams rather than tubes. A company, Kirk Precision Ltd, was established in Britain to manufacture both road bike and mountain bike frames with this technology. However, despite some early commercial success, there were problems with reliability and manufacture stopped in 1992.
The small number of modern magnesium frames in production are constructed conventionally using tubes.
Scandium
Some manufacturers of bikes make frames out of aluminum alloys containing scandiumScandium
Scandium is a chemical element with symbol Sc and atomic number 21. A silvery-white metallic transition metal, it has historically been sometimes classified as a rare earth element, together with yttrium and the lanthanoids...
, usually referred to simply as scandium for marketing purposes although the Sc content is less than 0.5%. Scandium improves the welding characteristics of some aluminum alloys with superior fatigue resistance permitting the use of smaller diameter tubing, allowing for more frame design flexibility.
Bamboo
Several bicycle frames have been made of bamboo tubes connected with metal or composite joinery. Aesthetic appeal has often been as much of a motivator as mechanical characteristics.Wood
Several bicycle frames have been made of wood, either solid or laminate. Although one survived 265 grueling kilometers of the Paris–Roubaix race, aesthetic appeal has often been as much of a motivator as ride characteristics. Wood is used to fashion bicycles in East Africa.Combinations
Combining different materials can provide the desired stiffness, compliance, or damping in different areas better than can be accomplished with a single material. The combined materials are usually carbon fiber and a metal, either steel, aluminum, or titanium. One implementation of this approach includes a metal down tube and chain stays with carbon top tube, seat tube, and seat stays. Another is a metal main triangle and chain stays with just carbon seat stays.Carbon forks have become very common on racing bicycles of all frame materials.
Butted tubing
Butted tubingButted tubing
Butted tubing is a bicycle construction design component. It is used to increase the thickness at the joints of the frame while allowing thinner metal or polymer everywhere else...
has increased thickness near the joints for strength while keeping weight low with thinner material elsewhere. For example, triple butted means the tube, usually of an aluminum alloy, has three different thicknesses, with the thicker sections at the end where they are welded. The same material can be used in handle bars.
Braze-ons
A variety of small features—bottle cageBottle cage
A bottle cage is device used to affix a water bottle to a bicycle. Composed of plastic, aluminum, stainless steel, titanium or carbon fiber, it is attached to the main frame of a bicycle, the handlebars, or behind the saddle...
mounting holes, shifter
Shifter (bicycle part)
A bicycle shifter or gear control or gear levers is a component used to control the gearing mechanisms and select the desired gear ratio. Typically, they operate either a derailleur mechanism or an internal hub gear mechanism. In either case, the control is operated by moving a cable that connects...
bosses, cable
Bowden cable
A Bowden cable is a type of flexible cable used to transmit mechanical force or energy by the movement of an inner cable relative to a hollow outer cable housing...
stops, pump
Bicycle pump
A bicycle pump is a type of positive-displacement pump specifically designed for inflating bicycle tires. It has a connection or adapter for use with one or both of the two most common types of valves used on bicycles, Schrader or Presta...
pegs, cable guide
Cable guide
A cable guide is a fitting or part of a bicycle frame which guides a piece of bare inner bowden cable around a corner. Most multi-speed bicycles have cable guides to get the derailleur cables past the bottom bracket....
s, etc. -- are described as braze-ons because they were originally, and sometimes still are, brazed
Brazing
Brazing is a metal-joining process whereby a filler metal is heated above and distributed between two or more close-fitting parts by capillary action. The filler metal is brought slightly above its melting temperature while protected by a suitable atmosphere, usually a flux...
on.
Suspension
Many bicycles, especially mountain bikes, have suspension built into the frame.See also
- BicycleBicycleA bicycle, also known as a bike, pushbike or cycle, is a human-powered, pedal-driven, single-track vehicle, having two wheels attached to a frame, one behind the other. A person who rides a bicycle is called a cyclist, or bicyclist....
- Bicycle chainBicycle chainA bicycle chain is a roller chain that transfers power from the pedals to the drive-wheel of a bicycle, thus propelling it. Most bicycle chains are made from plain carbon or alloy steel, but some are nickel-plated to prevent rust, or simply for aesthetics. Nickel also confers a measure of...
- Bicycle forkBicycle forkA bicycle fork is the portion of a bicycle that holds the front wheel and allows the rider to steer and balance the bicycle. A fork consists of two fork ends which hold the front wheel axle, two blades which join at a fork crown, and a steerer or steering tube to which the handlebars attach ...
- Bicycle suspensionBicycle suspensionA bicycle suspension is the system or systems used to suspend the rider and all or part of the bicycle in order to protect them from the roughness of the terrain over which they travel...
- Step-through frameStep-through frameA step-through frame is a type of bicycle frame, often used for utility bicycles, with a low or absent top tube or cross-bar....
External links
- Science of Cycling: Frames & Materials from the ExploratoriumExploratoriumThe Exploratorium is a museum in San Francisco with over 475 participatory exhibits, all of them made onsite, that mix science and art. It also aims to promote museums as informal education centers....
- Sheldon Brown's "Revisionist Theory of Bicycle Sizing" - an explanation of the different ways of measuring frame sizes.
- Metallurgy for Cyclists - discusses frame material properties in relation to suitability to frame use
- The Bicycle Forest's BikeCAD program allows you to design your own frame online.