Crankset - AbsoluteAstronomy.com

The crankset or chainset (in the UK), is the component of a bicycle drivetrain

Bicycle drivetrain systems

Bicycle drivetrain systems are used to transmit power on bicycles, tricycles, quadracycles, unicycles, or other human-powered vehicles from the riders to the drive wheels. Most also include some type of a mechanism to convert speed and torque via gear ratios....

that converts the reciprocating motion

Reciprocating motion

Reciprocating motion, also called reciprocation, is a repetitive up-and-down or back-and-forth motion. It is found in a wide range of mechanisms, including reciprocating engines and pumps. The two opposite motions that comprise a single reciprocation cycle are called strokes...

of the rider's leg

Human leg

The human leg is the entire lower extremity or limb of the human body, including the foot, thigh and even the hip or gluteal region; however, the precise definition in human anatomy refers only to the section of the lower limb extending from the knee to the ankle.Legs are used for standing,...

s into rotational motion used to drive 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...

, which in turn drives the rear 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....

. It consists of one or more sprocket

Sprocket

A sprocket or sprocket-wheel is a profiled wheel with teeth, cogs, or even sprockets that mesh with a chain, track or other perforated or indented material. The name 'sprocket' applies generally to any wheel upon which are radial projections that engage a chain passing over it...

s, also called chainrings
or chainwheels attached to the crank
Crank (mechanism)
A crank is an arm attached at right angles to a rotating shaft by which reciprocating motion is imparted to or received from the shaft. It is used to change circular into reciprocating motion, or reciprocating into circular motion. The arm may be a bent portion of the shaft, or a separate arm...

s, arms, or crankarms to which the pedals attach. It is connected to the rider by the pedal

Bicycle pedal

A bicycle pedal is the part of a bicycle that the rider pushes with their foot to propel the bicycle. It provides the connection between the cyclist's foot or shoe and the crank allowing the leg to turn the bottom bracket spindle and propel the bicycle's wheels...

s, to the bicycle frame by 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...

, and to the rear sprocket, cassette

Cassette (bicycle part)

On a bicycle, the cogset or cluster is the set of multiple rear sprockets that attaches to the hub on the rear wheel. A cogset works with a rear derailleur as part of the drivetrain to provide multiple gear ratios to the rider. Cogsets come in two varieties, cassettes or freewheels, of which...

or freewheel

Freewheel

thumb|Freewheel mechanismIn mechanical or automotive engineering, a freewheel or overrunning clutch is a device in a transmission that disengages the driveshaft from the driven shaft when the driven shaft rotates faster than the driveshaft...

via the chain.

Cranks

The two cranks, one on each side and usually mounted 180° out of phase, connect the bottom bracket axle to the pedals.

Sizes

Bicycle cranks can vary in length to accommodate different sized riders and different types of cycling. Crank length is measured from the center of the pedal spindle to the center of the bottom bracket spindle or axle. The larger bicycle component manufacturers typically offer crank lengths for adult riders from 165 mm to 180 mm long in 2.5 mm increments, with 170 mm cranks being the most common size. A few small specialty manufacturers make bicycle cranks in a number of sizes smaller than 165 mm and longer than 180 mm. Some manufacturers also make bicycle cranks that can be adjusted to different lengths. While logic would suggest that, all other things being equal, riders with shorter legs should use proportionally shorter cranks and those with longer legs should use proportionally longer cranks, this is not universally accepted. However, very few scientific studies have definitively examined the effect of crank length on sustained cycling performance and the studies' results have been mixed. Bicycle crank length has not been easy to study scientifically for a number reasons, chief among them is that cyclists are able to physiologically adapt to different crank lengths. Cyclists are typically more efficient pedalling cranks with which they have had an adaptation period. Several different formulas exist to calculate appropriate crank length for various riders. In addition to the rider's size, another factor affecting the selection of crank length is the rider's cycling specialty and the type of cycling event. Historically, bicycle riders have typically chosen proportionally shorter cranks for higher cadence cycling such as criterium and track racing, while riders have chosen proportionally longer cranks for lower cadence cycling such as time trial racing and mountain biking. However, the evolution of very low rider torso positions to reduce aerodynamic drag for time trial racing and triathlon cycling can also affect crank selection for such events. Some have suggested that proportionally shorter cranks may have a slight advantage for a rider with a very low torso position and an actute hip angle, especially as the rider pedals near the top-dead-center position of the pedal stroke.

Materials

Cranks are constructed of either an aluminum alloy, titanium

Titanium

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....

, carbon fiber

Carbon 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...

, chromoly steel, or some less expensive steel

Steel

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...

. Tubular steel cranks (such as Tioga's Revolver) can be light and very strong, are usually found on bmx bikes, and are slowly finding their way to mountain bikes (Dirt jumping and Urban assault) . Aluminum cranks may be cast, hot forged or cold forged ("cold" in this context means the billet from which the crank is to be made is heated to a specified temperature well below the melting point, not room temperature). Cold forging gives the metal additional strength, and the cranks can therefore be made lighter without increasing the risk of breakage. Shimano "Hollowtech" aluminum cranks are made by forging the main arms around a hard steel insert which is then withdrawn, leaving an internal void to save weight. They are then welded up before final machining.

To the bottom bracket

There are a variety of methods used to attach the cranks to the bottom bracket spindle (or axle).

Older cranks use a wedge-shaped pin, called a cotter, for attachment to the bottom bracket spindle.
Newer cranks slide onto
- a square tapered spindle. The taper is 2 degrees with respect to the centerline. There are at least two non-interchangeable dimensions (e.g. Shimano and Campagnolo use competing standards in square taper, viz. JIS and ISO respectively, where the ISO spindle is longer and its taper end is slightly smaller. Most parts made by European manufacturers are to the ISO standard, and most Asian manufacturers use the JIS (Shimano) standard), and two orientations: diamond and square.
- a hexagonal tapered spindle (Tune components cranks are an example)
- a splined
  Rotating spline
  Splines are ridges or teethon a drive shaft that mesh with grooves in a mating piece and transfer torque to it, maintaining the angular correspondence between them....
  
  bottom bracket spindle with two prominent specifications, and numerous uncommon ones. The ISIS spline may be the most common splined standard as it was decided on and supported by several companies. Shimano's Octalink is a common proprietary standard that comes in two forms: version one for XTR, 105, Ultegra and Dura Ace; and version two for every other groupset such as XT, LX and Deore. Truvative and DMR also have their own proprietary spline interface standards. A 48 splined spindle, such as from Profile Racing, Demolition, and Eighth Inch, is mostly used for BMX
  BMX
  Bicycle motocross or BMX refers to the sport in which the main goal is extreme racing on bicycles in motocross style on tracks with inline start and expressive obstacles, and it is also the term that refers to the bicycle itself that is designed for dirt and motocross cycling.- History :BMX started...
  
  , unicycle
  Unicycle
  A unicycle is a human-powered, single-track vehicle with one wheel. Unicycles resemble bicycles, but are less complex.-History:One theory of the advent of the unicycle stems from the popularity of the penny-farthing during the late 19th century...
  
  s, and fixed-gear
  Fixed-gear bicycle
  A fixed-gear bicycle is a bicycle that has no freewheel, meaning it cannot coast, as the pedals are always in motion when the bicycle is moving....
  
  Freestyle.

The cranks are pressed into place and prevented from squirming off via fretting

Fretting

Fretting refers to wear and sometimes corrosion damage at the asperities of contact surfaces. This damage is induced under load and in the presence of repeated relative surface motion, as induced for example by vibration...

by a bolt or nut installed into or onto the bottom bracket spindle. The head of the bolt or the nut sit inside a counterbore

Counterbore

A counterbore can refer to a cylindrical flat-bottomed hole, which enlarges another hole, or the tool used to create that feature. A spot face is a very shallow counterbore...

that is also threaded to accept a crank puller tool. The counterbore is often covered with a dust cover.

One solution to the issue of fretting is to use a metal based anti-seize lubricant between the mating parts. Composed of assorted mixtures of aluminum, copper, graphite and nickel powders in a grease base, such lubrication allows repeated assembly and dis-assembly without wear and the elimination of fretting corrosion during use.

Even newer designs have the bottom bracket spindle, usually hollow and larger diameter than is possible for bottom brackets with bearings held inside the bottom bracket shell of a bike frame, for reduced weight and increased stiffness, permanently attached to the right crank (Shimano and others) or the left crank (Race Face). The left crank slides onto a spline and is tightened with one or more pinch bolts (Shimano) or is pressed onto a spline by a bolt on the bottom bracket spindle (Race Face).
The latest from Campagnolo
Campagnolo
Campagnolo is an Italian manufacturer of high-end bicycle components with headquarters in Vicenza, Italy. The components are organised as groupsets and are a near-complete collection of a bicycle's mechanical parts. Campagnolo's flagship components are the Super Record, Record, and Chorus...

, called Ultra-Torque^{TM, has each crank permanently attached to one half of the spindle (called semi-axles) which then join in the middle of the bottom bracket with a Hirth jointHirth joint
A Hirth joint or Hirth coupling is a type of mechanical connection named after its developer Hellmuth Hirth. It is used to connect two pieces of a shaft together and is characterized by teeth that mesh together on the end faces of each half shaft....

and a bolt.}
Certain companies such as Cannondale (BB30 open standard, introduced in 2000) have made their own unique bottom bracket standards requiring changes in the bottom bracket shell of the bicycle frame in order to accommodate the bottom bracket/crank design. The open BB30 standard is gaining popularity on high end bicycle and component manufacturers (Zipp, Specialized, FSA).
Finally, many children's bikes and older, or less-expensive bikes have one-piece ("Ashtabula") cranks where the two cranks and bottom bracket spindle are forged as one piece of steel (see photograph above).

See the bottom bracket article for more details.

To the pedals

Crank arms have a threaded hole (or "eye") at their outboard end to accommodate the pedal spindle. Adult or multi-piece cranks have a 9/16 inch hole with 20 TPI (a combination that appears to be unique to this application). One-piece or children's cranks use a 1/2 inch hole. Some cranks on children's bikes have more than one pedal hole so that the pedal can be moved to accommodate growth.

The right-side (usually the chain side) hole is right-hand threaded, and the left-side hole is left-hand (reverse) threaded to help prevent it from becoming unthreaded by an effect called 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...

.

Pedal spindles are hard steel, and gradually fret and erode the crankarm where the two meet. This can eventually be a cause of crank breakage, which commonly occurs at the pedal eye. Some manufacturers advise the use of a thin steel washer between the pedal and crank, but this is ineffective because the hard washer frets against the crank instead. A solution, suggested by Jobst Brandt, is to use a 45 degree taper at the surface where crank and pedal meet, as this would eliminate precession-induced fretting and loosening (it is already done for most automobile lug nut

Lug nut

A lug nut is a fastener, specifically a nut, used to secure a wheel on a vehicle. Typically, lug nuts are found on automobiles, trucks , and other large vehicles utilizing rubber tires.-Design:...

s for the latter reason). However, this would require manufacturers to change a well-established standard which currently allows most pedals to be fitted to most cranks.

The solution to the issue of fretting is to use a metal based anti-seize lubricant; being composed of assorted mixtures of aluminium, copper, graphite and nickel powders in a grease base - that allows repeated assembly and disassembly without wear and the elimination of fretting corrosion during use.

Spider

On older styles, the spider—the multi-armed piece that connects the chainring to the bottom bracket axle—was a separate piece from the crank arm. The most common modern cranks have an integrated spider on the drive-side crank arm. However, Middleburn, TA, and Surly

Surly Bikes

Surly Bikes is a designer and importer of bicycles, frames, parts, and accessories based in Bloomington, Minnesota, established circa 1998. Surly is owned by and shares facilities with Quality Bicycle Products ....

currently produce cranks with separate detachable spiders, enabling a wide variety of chainring patterns to be used with the same cranks.

Spiders usually have 4 or 5 arms, although some models have had as few as 3 and many as 10 arms with 6 having been popular in the past.

Bolt circle diameter (BCD)

Many modern bicycles have removable chainrings, to allow for replacement when worn, or to change the gear ratio provided (although the change is limited).

The holes on the spider arms used for attaching a chainring can have a variety of dimensions, referred to as the bolt circle diameter, commonly abbreviated as BCD. This measurement is sometimes referred to as pitch-circle diameter (PCD). Cranks designed to mount one or two chainrings will almost always use a single bolt circle diameter. Cranks designed to mount three chainrings will almost always use two different bolt circle diameters; the larger to mount the two outer rings and the smaller to mount the inner ring. Most modern two-chainring cranks use either a 110mm or 130mm bolt circle diameter.

Bolt circle diameters of common cranks:

Single : 130, 135, or 144 BCD
Road double : 130 BCD (Shimano and others), or 135 (Campagnolo)
Road triple : 130/74 BCD (Shimano and others), or 135/74 BCD (Campagnolo)
Compact/touring double : 110 BCD or (Campagnolo carbon 4×110/1×113 BCD)
Compact/touring triple : 110/74 BCD
Mountain bike (4 arm): 104/64 BCD
Mountain bike (5 arm standard) : 110/74 BCD
Mountain bike (5 arm compact) : 94/58 BCD

For an extensive list of bolt circle diameters and their applications, see Sheldon Brown

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...

's Bolt Circle Diameter Crib Sheet.

Chainrings (also called "chain rings", "chainwheels" or "sprockets", although sprocket is used this way mostly in the BMX

BMX

Bicycle motocross or BMX refers to the sport in which the main goal is extreme racing on bicycles in motocross style on tracks with inline start and expressive obstacles, and it is also the term that refers to the bicycle itself that is designed for dirt and motocross cycling.- History :BMX started...

community) engage the chain

Bicycle chain

to transfer power to the (usually rear) wheel

Bicycle wheel

. They usually have teeth spaced to engage every link of the chain as it passes over; however, in the past, some designs (called skip-tooth or inch-pitch) have had one tooth for every other link of the chain.

Sizes

By convention, the largest chainring is outboard and the smallest is inboard. Chainrings vary in size from as few as 20 teeth to as many as 55 or potentially more.

Chainrings also come in several nominal widths:

3/16" (4.76 mm) for old-time bikes (especially skip-tooth or inch-pitch), heavy duty BMX, Worksman
Worksman Cycles
Worksman Cycles is an American manufacturer of bicycles and tricycles for industrial, commercial and recreational use. The company was founded in 1898 and is located in Ozone Park in the borough of Queens in New York City...

, and exercise bikes
1/8" (3.18 mm) for track, BMX, cruiser bikes, one-speed, three-speeds, and the rare derailleur bike.
3/32" (2.38 mm) for road, hybrid, mtb bikes, single-speed and 5-, 6-, 7-speed freewheels.
5/64" (1.98 mm) for any bike with 9- or 10-speed cassettes

Materials

Chainrings are constructed of either an aluminum alloy, titanium, steel, or carbon fiber.

Construction

Cheaper cranksets may have the chainrings welded or riveted directly to the crank arm or spider. More expensive sets have the chainrings bolted on so that they can be replaced if worn or damaged, or to provide different gearing.

Replacement chainrings must be chosen with a bolt-hole count and spacing that matches the spider.

Chainrings designed for use with multi-chainring crank arms may have ramps or pins to aid in shifting. The middle chain ring, in the case of a triple crankset, usually has the most shaping to aid in shifting up and down. The smallest chainring usually has the least, if any shaping.

Tandem cranksets

On tandem bicycle

Tandem bicycle

The tandem bicycle or twin is a form of bicycle designed to be ridden by more than one person. The term tandem refers to the seating arrangement , not the number of riders. A bike with two riders side-by-side is called a sociable.-History:Patents related to tandem bicycles date from the late 19th...

s the pedalling contribution of both riders is often combined and coordinated by the crank arms. There may be a second set of chain rings, often on the opposite side from the regular drive train, one on each crank set and connected by a separate chain. The most common implementation has both cyclists pedaling at exactly the same pace and usually in phase, although it is possible to configure the system for out-of-phase pedaling.

The most common tandem crankset is a set of four cranks. Both left cranks have spiders and chainrings to be connected by a timing chain, and only one of the right cranks has a spider for the drive chain.

There are tandem cranksets available called independent pedaling system cranksets, which allow each cyclist to pedal, or not, at their own pace.

Chain guards

Some cranksets incorporate a chain guard that consists simply of a plastic or metal ring outboard of the largest chainring and slightly larger in diameter to help prevent the chain from touching or catching clothing. Bicycles that are going to be used in abusive applications, such as freeride

Freeride

Freeride is a discipline of mountain biking closely related to downhill cycling and dirt jumping focused on tricks, style, and technical trail features. It is now recognized as one of the most popular disciplines within mountain biking....

and BMX

BMX

, will often incorporate a very heavy-duty chain guard that is designed to protect the chainrings from physical damage caused by impact with fixed objects; also called 'bashguards', these commonly replace a third (large) chainring.

Chainguides

Some cranksets used for freeride

Freeride

and downhill

Downhill cycling

Downhill biking is a gravity-assisted time trial mountain biking event. Riders race against the clock, usually starting at intervals of 30 seconds , on courses which typically take two to five minutes to complete. Riders come from all around the world. Riders are timed with equipment similar to...

mountain biking have a chainguide installed. A chainguide is a metal or plastic housing that keeps the chain on the chainrings over rough terrain and during technical riding. Most chainguides are designed for only one front chainring, but there are a few dual-ring chainguides available such as the E13 DRS and MRP LRP. Chainguides include a channel on the top of the chainring to keep the chain in line (for models designed for one front chainring) and a roller or sprocket on the bottom to help keep the chain engaged with the chainring. These are almost always used in conjunction with bashguards. Exceptions including the E.thirteen LG-1 and the MRP G2 (and now the G2 SL) do exist which use integrated skid plates, removing impact forces from the crank's spider and transferring them to the frame.

Freewheeling cranksets

Some cranksets have been produced that incorporate a ratcheting mechanism to accommodate coasting. In this case, the chain continues to rotate with the rear wheel when the rider stops pedaling. The ultimate goal of freewheeling cranks is to allow the rider to shift the chain while coasting. Shimano's discontinued FF system (Front Freewheeling

Front freewheel

The Shimano front freewheel design was an innovative bicycle drivetrain design of the 1970s. To improve the normal bicycle with a freewheel between the rear sprocket cluster and wheel hub, Shimano inserted a freewheel between the pedal cranks and the front chainrings that enabled the rider to shift...

) is one of the more commonly seen examples.

Left-side-drive

This configuration consists of a left crank arm with a spider and chainring, and a right crank arm without a spider. This is exactly the opposite of a normal configuration. The special crankset must also be paired with a rear hub that can be driven from the left side. These hubs typically have left hand threads for a special freewheel, which is also threaded left hand and ratchets the opposite direction of a normal freewheel. If the freewheel and hub were threaded with right hand threads, the torque applied by pedaling would loosen and unthread the freewheel from the hub.

Left-side-drive is sometimes done with a fixed gear drivetrain. Because a correctly installed track sprocket can not be loosened from the hub no matter which way torque is applied, it can be used for left-side drive without requiring special left hand threaded parts.

Note that a normal right-side-drive crankset can not be installed backwards to create a left-side-drive bicycle because the threaded pedal

Bicycle pedal

holes at the end of the crank arms would be backwards of normal. Even though some kinds of pedals could simply be installed on the wrong sides to get around this issue, precession

Precession

Precession is a change in the orientation of the rotation axis of a rotating body. It can be defined as a change in direction of the rotation axis in which the second Euler angle is constant...

would tend to loosen them over time, causing the pedals to become detached and/or damaging the pedal threading in the crank arms. A front crankset designed for tandem use is a commercially available option, since this has a chainring for the timing chain on the left side. Choice of chainring sizes may be limited.

Independent crank arms

At least one manufacturer offers a crankset in which the crank arms may rotate independently. This is supposed to aid in training by requiring each leg to move its own pedal in a full circle. One independent study has demonstrated training with these cranks can improve cycling efficiency. The manufacture also claims that this change can also be useful to aid in running improvement, help prevent injuries in runners, improve core strength development, and are useful for the rehabilitation of lower extremity injuries, especially in the athlete. The manufacturer claims these cranks have been used as a training tool by several World and Olympic Champions in both cycling and triathlon and several professional sports teams including MLB and NFL teams, and other uses.

Non Round chainrings

Several manufacturers have tried non-round chainrings, such as Shimano's Biopace

Biopace

Biopace is a tradename for a type of ovoid bicycle chain ring manufactured by Shimano from 1983 to 1993 The design was intended to help overcome the "dead zone" where the crank arms are vertical and riders have little mechanical advantage...

, Rotor's Q-Rings and Osymetric's Harmonic ring. These are designed to provide varying mechanical advantage

Mechanical advantage

Mechanical advantage is a measure of the force amplification achieved by using a tool, mechanical device or machine system. Ideally, the device preserves the input power and simply trades off forces against movement to obtain a desired amplification in the output force...

at different points in the pedal stroke, effectively changing the gear ratio at different angles of rotation with the intention to be more ergonomic. Non-round chainrings can sometimes cause problems in front shifting.

Their significant popularity in the late eighties to early nineties is best reflected in their widespread use by professional cyclists of that time. However, one hold-out has been Team CSC Saxo Bank veteran Bobby Julich

Bobby Julich

Robert Julich, most commonly referred to as Bobby Julich, is an American former professional road bicycle racer who last rode for Team CSC in the UCI ProTour racing series. He got his international breakthrough when he finished 3rd overall in the 1998 Tour de France race, but has since ridden...

, and there are still a couple of pro riders that use them as late as 2011. Notably Bradley Wiggins

Bradley Wiggins

Bradley Marc Wiggins, CBE is a British professional track and road bicycle racer, currently riding for Team Sky. Wiggins' career began on the track, where he specialised in the pursuit and madison disciplines....

of Team SKY, David Millar of Team Garmin Transitions and Agritubel's Geoffrey Lequatreall riding the Osymetric brand and Team CSC Saxo Bank's Carlos Sastre

Carlos Sastre

Carlos Sastre Candil is a retired Spanish professional road bicycle racer and champion of the 2008 Tour de France. Sastre rides in 2011 for UCI Professional Continental team...

with Rotor's Q-Rings from his native Spain. Sastre won the 2008 Tour de France with Q-rings. Bradley Wiggins of the Garmin Slipstream team used an oval chainring from Osymetric in his TT bike (Felt DA) in the 2009 Tour de France.
In the 2010 Giro D'Italia

Giro d'Italia

The Giro d'Italia , also simply known as The Giro, is a long distance road bicycle racing stage race for professional cyclists held over three weeks in May/early June in and around Italy. The Giro is one of the three Grand Tours , and is part of the UCI World Ranking calendar...

, and David Millar used them in his 2011 victory in the final TT of the 2011 Giro. Several Pro-Tour teams were using Osymetric and Q-Rings ovoid chainrings for road racing and time trialing.

Compact crankset

In the context of mountain biking

Mountain biking

Mountain biking is a sport which consists of riding bicycles off-road, often over rough terrain, using specially adapted mountain bikes. Mountain bikes share similarities with other bikes, but incorporate features designed to enhance durability and performance in rough terrain.Mountain biking can...

the term compact crankset, or micro drive

Micro drive

Micro drive is a term used to describe the drivetrain, mostly BMX and MTB, that use smaller than standard sized cogs. The smallest rear sprocket that fits on a freehub body is an 11-tooth, but with the use of a cassette hub, sometimes called a micro drive rear hub, sprockets as small as 8 teeth may...

, refers to smaller triple cranksets, giving a small benefit in weight at the expense of increased wear and also giving the bike better clearance over obstacles. Typical ratios would be 22/32/44 teeth as opposed to 28/38/48 or 24/36/46 teeth. These would be used with smaller cassettes (Generally cassettes are available with 11 tooth minimum gear sizes for compact chainsets while standard chainsets were designed for cassettes with a 13 or 14 tooth top gear), giving the same overall ratio. Compact chainrings are the dominant standard for mountain bike cranks for the past decade or so.

In the context of road cycling

Road cycling

Road cycling is the most widespread form of cycling. It includes recreational, racing, and utility cycling. Road cyclists are generally expected to obey the same rules and laws as other vehicle drivers or riders and may also be vehicular cyclists....

, compact drivetrain typically refers to double cranksets with a smaller (usually 110mm) bolt circle diameter than the standard 130mm or Campagnolo's 135mm. As of 2006, all of the major component manufacturers such as Shimano

Shimano

Shimano, Inc. is a Japanese multinational manufacturer of cycling components, fishing tackle, and rowing equipment.In 2005, the company had net sales of US $1.4 billion. Bicycle components provided 75% of its sales income...

and Campagnolo offer compact cranks in their midrange and high-end product lines. The compact crankset provides a compromise between the standard road double crankset (with 39/52 or 39/53 tooth chainrings) and the road triple (with 30/42/52 or 30/39/53 tooth chainrings). The compact crankset has two chainrings and typical ratios are 34/48, 34/50 and 36/50. This provides nearly the same lower gear ratios as a triple but without the need for a third chainring, a triple front derailleur and a long cage rear derailleur. Both Shimano and Campagnolo recommend and sell front derailleurs specifically designed for compact cranksets, claiming better shifting.

Compact gearing is not necessarily lower than standard gearing if cassettes with smaller sprockets (such as 11–23) are used. A high gear of 50×11 on a compact drivechain is actually slightly higher than the 53×12 of a standard set.

Compact gearing usually has a large percentage jump between the two chainrings. In balance, it may also allow small jumps in the rear by allowing a closer ratio cassette to be used, except for the 9% jump at the high end between the 11 and 12 tooth sprockets.

Bent crankarms

Marketed and known by a variety of names (Z-cranks, P.M.P cranks, etc.) non-straight crank arms have been introduced several times. However, "as long as the distance from crank axle to pedal is fixed, there is no pedaling advantage in using bent crank arms". Possible disadvantages from comparable straight crank arms include more weight and more flex.

Rotor crank

Rotor is a trade name of a type of crank used in the transmission system of a bicycle. Unlike a standard pair of cranks that always remain at 180 degrees relative to each other, the Rotor system varies this angle through the circle of motion. The manufacturer claims that by reducing the time each crank spends in the top and bottom "dead spots", where little or no force is available from the leg, power output relative to heart rate is increased, amongst other claimed benefits.

The Rotor crank was developed by Aeronautic Engineering School students in Madrid, Spain in 1995 and was later commercialised. While Rotor cranks have found success with town and cargo cyclists, many competitive cyclists continue to use the traditional fixed system as offered by major manufacturers Campagnolo

Campagnolo

Campagnolo is an Italian manufacturer of high-end bicycle components with headquarters in Vicenza, Italy. The components are organised as groupsets and are a near-complete collection of a bicycle's mechanical parts. Campagnolo's flagship components are the Super Record, Record, and Chorus...

and Shimano

Shimano

, amongst others. One major factor is weight—Rotor cranks are 50%–75% heavier than most competitive cranks. Another factor is that a cyclist with more than one bike needs to change them all to the Rotor system, which can be expensive, and adaptation to the Rotor pedaling style can take around a week ^[Source?]. Many competitive cyclists, including Cervélo TestTeam

Cervélo TestTeam

Cervélo TestTeam is a former professional cycling team, whose license was held in Switzerland by the cycling management company Cycling United Racing. The team's title sponsor was Cervélo, a Canadian manufacturer of bicycle frames that previously exclusively supplied...

, use Rotor's Q-rings which provide many of the same benefits without the added weight.

Planetary-drive

A planetary-gear

Epicyclic gearing

Epicyclic gearing or planetary gearing is a gear system consisting of one or more outer gears, or planet gears, revolving about a central, or sun gear. Typically, the planet gears are mounted on a movable arm or carrier which itself may rotate relative to the sun gear...

crankset offers two different gear ratios with just one chainring. This can have at least two advantages: shifting while not pedalling and fewer chances for the chain to come off the chainring. The Mountain Drive & Speed-Drive by Schlumpf Innovations and the Hammerschmidt are examples.

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