Wheel sizing
Encyclopedia
The wheel size for a motor vehicle
or similar wheel
has a number of parameters.
s or wheel stud
s on the wheel hub
. As the bolts are most often evenly spaced, the number of bolts determines the pattern. For example: smaller cars have three (Citroën 2CV
, Renault 4
, some Peugeot 106
s and Citroën Saxo
s, and the Tata Nano
). Compact car
s may have four bolts. Most United States passenger cars have five bolts. Pickup trucks and large SUV
s can have as many as six or eight.
determined by the positions of the bolts. The center of every bolt lies on the circumference
of the bolt circle. The important measurement is the bolt circle diameter
(BCD), also called the pitch circle diameter (PCD).
The BCD may be expressed in millimeters or inches, and is usually given with the number of bolts. For example, a 1974 MG B has a 4/4.5 inch (4/114.3 mm) wheel hub, meaning it has a 4-bolt pattern with a 4.5 inch (114.3 mm) bolt circle diameter.
The most common BCD values are 100 mm (≈3.94 inches) and 4.5 inches (114.3 mm).
Special BCD values are: 95.25 mm (for MGF and Rover Metro), 98 mm (for Fiat group automobiles), 101 mm (for Mini, MG, Austin Metro), 100 or 105 mm (for some GM vehicles), 108 mm (mostly for PSA, Ford and Lincoln), 110 mm (for some GM vehicles), 112 mm (for Mercedes-Benz and some VW group vehicles), 115 mm (for some GM vehicles), 120 mm (mostly for BMW), 130 mm (for Porsche), 170 mm (for Saab 96
).
Some basic geometry is needed to find the center of a 5-bolt pattern. In practice, the BCD can be found by multiplying the center distance between any two adjacent holes by 1.701.
Generally, the BCD b can be calculated for any wheel from the number of bolts n and the center distance d between two adjacent bolts as:
.
s on wheel stud
s, or bolts. Lug (aka wheel nuts in British English) nuts are usually either flat, tapered (generally at 60 degrees and referred to as conical seat), or ball seats, meaning the mounting surfaces are flat, tapered, or spherical respectively.
Most Mercedes
have ball lug seats from the factory while most aftermarket wheels have a tapered lug design. Wrong lug nuts for the wheel will not properly center it and cause wobble. Some manufacturers (e.g. Toyota and Lexus) have used taper lug nuts for steel wheels and flat seated lug nuts for alloy wheel
s.
Some aftermarket wheels will only fit smaller lug nuts, or not allow an ordinary lug nut to be properly torqued down
because a socket will not fit into the lug hole. Tuner lug nuts were created to solve this problem by utilizing a special key to allow removal and installation with standard lug wrench or socket. The design of tuner lug nuts can range from bit style to multisided or spline drive, and are sometimes lightweight for performance purposes.
A variation is the "locking wheel nut", which is almost universally used for alloy wheels in the United Kingdom. One standard lug nut on each wheel is replaced with a nut which requires a special and unique key (typically a computer-designed, rounded star shape) to fit and remove the nut. This helps to discourage theft of wheels. However, universal removal tools are available which grip the head of the locking nut using a hardened left-hand thread. The success of these depends on whether there is room to use it in the lug hole, and whether the manufacturer has incorporated a free-spinning outer casing to the lock. Keeping an appropriate tool to lock and unlock aftermarket nuts, and a spare set of nuts, with the spare tire in the boot of the car is recommended by manufacturers.
, measured in millimeters, can be negative or positive, and is the distance from the hub-mounting surface to the rim's true centerline. A positive offset means the hub-mounting surface is closer to the outside edge of the wheel, i.e. the wheel wraps around the hub and brake hardware more deeply; a negative offset means the hub-mounting surface is closer to the inside edge of the wheel and wheel sticks outwards more than inwards.
When selecting aftermarket wheels, a wheel with too little positive offset will be closer to edge of the fender, and one with too much positive offset will tuck inside the fender and be closer to the suspension components. Wheel width, offset and tire size all determine the way a particular wheel/tire combination will work on a given car. Offset also affects the scrub radius
of the steering and it is advisable to stay within the limits allowed by the vehicle manufacturer. Because wheel offset changes the lever-arm length between the center of the tire and the centerline of the steering knuckle, the way bumps, road imperfections and acceleration and braking forces are translated to steering torques (bump-steer, torque-steer, etc.) will change depending on wheel offset. Likewise, the wheel bearings will see increased thrust loads if the wheel centerline is moved away from the bearing centerline.
The wheel size is the diameter of the wheel in inches where the beads of the tire sit on the wheel. This measurement does not include the rim flange. Modern road tires have several measurements associated with their size as specified by tire code
s like 225/70R14. The first number in the code (e.g., "225") represents the nominal tire width in millimeters. This is followed by the aspect ratio (e.g.,"70"), which is the height of the side wall expressed as a percentage of the nominal width. "R" stands for radial and relates to the tire construction. The final number in the code (e.g.,"14") is the rim size measured in inches. The overall circumference of the tire will increase by increasing any of the tire's specifications. For example increasing the width of the tire will also increase its circumference, because the side wall height is a proportional length. Increasing the aspect ratio will increase the height of the tire and hence the circumference.
Off-roading
tires may use a different measurement scheme: outside diameter times(by) tread width, followed by rim size (all in inches) - for example 31x10.50R15. The size of the disc however is denoted like 8.5" X 20.0". This shall mean that the width (of thickness) of the wheel is 8.5 inches and the diameter is 20 inches.
A dub is a custom wheel that has a wheel size of 20 inches or greater; the term dub is a slang term for twenty. DUBS may have originated as an abbreviation for double-deuces, or 22 in wheels. DUB Magazine
, an automotive enthusiasts magazine, takes its name from the term and covers material chiefly pertaining to urban vehicles and the people that own them.
Centerbore on aftermarket wheels must be equal to or greater than that of the hub, otherwise the wheel cannot be mounted on the car. Many aftermarket wheels come with "hubcentric rings" that lock or slide into the back of the wheel to adapt a wheel with a larger centerbore to a smaller hub. These adapters are usually made of plastic but also in aluminum.
and caliper assembly.
. In the United States this information is required to be on the vehicle's door placard. The load capacity of the total number of wheels on the vehicle combined must meet or exceed the vehicle's GVWR.
Motor vehicle
A motor vehicle or road vehicle is a self-propelled wheeled vehicle that does not operate on rails, such as trains or trolleys. The vehicle propulsion is provided by an engine or motor, usually by an internal combustion engine, or an electric motor, or some combination of the two, such as hybrid...
or similar wheel
Wheel
A wheel is a device that allows heavy objects to be moved easily through rotating on an axle through its center, facilitating movement or transportation while supporting a load, or performing labor in machines. Common examples found in transport applications. A wheel, together with an axle,...
has a number of parameters.
Bolt pattern
The bolt pattern is the number of lug nutLug 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 or wheel stud
Wheel stud
Wheel studs are the threaded fasteners that hold on the wheels of many automobiles. They are semi-permanently mounted directly to the vehicle hub, usually through the brake drum or brake disk. Lug nuts are fastened over to the wheel stud to secure the wheel...
s on the wheel hub
Wheel hub assembly
Wheel hub assembly , also referred to as hub assembly, wheel hub unit, wheel hub bearing, etc., is an automotive part used in most cars, passenger vehicles and light and heavy trucks....
. As the bolts are most often evenly spaced, the number of bolts determines the pattern. For example: smaller cars have three (Citroën 2CV
Citroën 2CV
The Citroën 2CV |tax horsepower]]”) was an economy car produced by the French automaker Citroën between 1948 and 1990. It was technologically advanced and innovative, but with uncompromisingly utilitarian unconventional looks, and deceptively simple Bauhaus inspired bodywork, that belied the sheer...
, Renault 4
Renault 4
The Renault 4, also known as the 4L , is a hatchback economy car produced by the French automaker Renault between 1961 and 1992. It was the first front-wheel drive family car produced by Renault....
, some Peugeot 106
Peugeot 106
The Peugeot 106 is a supermini produced by French automaker Peugeot from 1991 to 2004.-Phase I:The Peugeot 106 was introduced on 12 September 1991, as the French marque's entry level car slotting in beneath the 205 - although it is now largely considered the 'true' replacement to the 205. It was a...
s and Citroën Saxo
Citroën Saxo
The Citroën Saxo is a supermini produced by the French manufacturer Citroën from 1996 to 2003. It was also sold in Japan as the Citroën Chanson. It shares many engine and body parts with the Peugeot 106 , the major difference being interiors and body panels...
s, and the Tata Nano
Tata Nano
The Tata Nano is an inexpensive, rear-engined, four-passenger city car built by the Indian company Tata Motors and is aimed primarily at the Indian domestic market....
). Compact car
Compact car
A compact car , or small family car , is a classification of cars which are larger than a supermini but smaller than or equal to a mid-size car...
s may have four bolts. Most United States passenger cars have five bolts. Pickup trucks and large SUV
Sport utility vehicle
A sport utility vehicle is a generic marketing term for a vehicle similar to a station wagon, but built on a light-truck chassis. It is usually equipped with four-wheel drive for on- or off-road ability, and with some pretension or ability to be used as an off-road vehicle. Not all four-wheel...
s can have as many as six or eight.
Bolt circle
The bolt circle is the notional circleCircle
A circle is a simple shape of Euclidean geometry consisting of those points in a plane that are a given distance from a given point, the centre. The distance between any of the points and the centre is called the radius....
determined by the positions of the bolts. The center of every bolt lies on the circumference
Circumference
The circumference is the distance around a closed curve. Circumference is a special perimeter.-Circumference of a circle:The circumference of a circle is the length around it....
of the bolt circle. The important measurement is the bolt circle diameter
Diameter
In geometry, a diameter of a circle is any straight line segment that passes through the center of the circle and whose endpoints are on the circle. The diameters are the longest chords of the circle...
(BCD), also called the pitch circle diameter (PCD).
The BCD may be expressed in millimeters or inches, and is usually given with the number of bolts. For example, a 1974 MG B has a 4/4.5 inch (4/114.3 mm) wheel hub, meaning it has a 4-bolt pattern with a 4.5 inch (114.3 mm) bolt circle diameter.
The most common BCD values are 100 mm (≈3.94 inches) and 4.5 inches (114.3 mm).
Special BCD values are: 95.25 mm (for MGF and Rover Metro), 98 mm (for Fiat group automobiles), 101 mm (for Mini, MG, Austin Metro), 100 or 105 mm (for some GM vehicles), 108 mm (mostly for PSA, Ford and Lincoln), 110 mm (for some GM vehicles), 112 mm (for Mercedes-Benz and some VW group vehicles), 115 mm (for some GM vehicles), 120 mm (mostly for BMW), 130 mm (for Porsche), 170 mm (for Saab 96
Saab 96
For the modern car, see Saab 9-6The Saab 96 is an automobile made by Saab. It was introduced in 1960 and was produced until January 1980, a run of 20 years. Like the 93 it replaced, the 96 was a development from the old Saab 92 chassis and, on account of its improvements and modernisation, it...
).
Determining the bolt circle
For a 4- or 6-bolt wheel, this measurement is merely the distance between the center of two diametrically opposite bolts. In the 4-bolt picture to the right, this would be the distance between holes #1 and #4, for example.Some basic geometry is needed to find the center of a 5-bolt pattern. In practice, the BCD can be found by multiplying the center distance between any two adjacent holes by 1.701.
| BCD geometry of 5-bolt pattern |
|---|
 or  half the top angle of a 5-bolt wheel is:  using a unity center distance of 1, a bolt center diameter = 2 × radius, and sin(36) = 0.58778:  |
Generally, the BCD b can be calculated for any wheel from the number of bolts n and the center distance d between two adjacent bolts as:
.Lug nuts or bolts
Wheels must be fitted with the correct type of lug nutLug 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 on wheel stud
Wheel stud
Wheel studs are the threaded fasteners that hold on the wheels of many automobiles. They are semi-permanently mounted directly to the vehicle hub, usually through the brake drum or brake disk. Lug nuts are fastened over to the wheel stud to secure the wheel...
s, or bolts. Lug (aka wheel nuts in British English) nuts are usually either flat, tapered (generally at 60 degrees and referred to as conical seat), or ball seats, meaning the mounting surfaces are flat, tapered, or spherical respectively.
Most Mercedes
Mercedes-Benz
Mercedes-Benz is a German manufacturer of automobiles, buses, coaches, and trucks. Mercedes-Benz is a division of its parent company, Daimler AG...
have ball lug seats from the factory while most aftermarket wheels have a tapered lug design. Wrong lug nuts for the wheel will not properly center it and cause wobble. Some manufacturers (e.g. Toyota and Lexus) have used taper lug nuts for steel wheels and flat seated lug nuts for alloy wheel
Alloy wheel
Alloy wheels are automobile wheels which are made from an alloy of aluminium or magnesium. They are typically lighter for the same strength...
s.
Some aftermarket wheels will only fit smaller lug nuts, or not allow an ordinary lug nut to be properly torqued down
Torque wrench
A torque wrench is a tool used to precisely apply a specific torque to a fastener such as a nut or bolt. It is usually in the form of a socket wrench with special internal mechanisms. It was invented by Conrad Bahr in 1918 while working for the New York City Water Department...
because a socket will not fit into the lug hole. Tuner lug nuts were created to solve this problem by utilizing a special key to allow removal and installation with standard lug wrench or socket. The design of tuner lug nuts can range from bit style to multisided or spline drive, and are sometimes lightweight for performance purposes.
A variation is the "locking wheel nut", which is almost universally used for alloy wheels in the United Kingdom. One standard lug nut on each wheel is replaced with a nut which requires a special and unique key (typically a computer-designed, rounded star shape) to fit and remove the nut. This helps to discourage theft of wheels. However, universal removal tools are available which grip the head of the locking nut using a hardened left-hand thread. The success of these depends on whether there is room to use it in the lug hole, and whether the manufacturer has incorporated a free-spinning outer casing to the lock. Keeping an appropriate tool to lock and unlock aftermarket nuts, and a spare set of nuts, with the spare tire in the boot of the car is recommended by manufacturers.
Offset
The offsetOffset (wheel)
The offset of a vehicle's wheel is the distance between the centerline of the wheel and the plane of the hub-mounting surface of the wheel. It can thus be either positive or negative, and is typically measured in millimeters...
, measured in millimeters, can be negative or positive, and is the distance from the hub-mounting surface to the rim's true centerline. A positive offset means the hub-mounting surface is closer to the outside edge of the wheel, i.e. the wheel wraps around the hub and brake hardware more deeply; a negative offset means the hub-mounting surface is closer to the inside edge of the wheel and wheel sticks outwards more than inwards.
When selecting aftermarket wheels, a wheel with too little positive offset will be closer to edge of the fender, and one with too much positive offset will tuck inside the fender and be closer to the suspension components. Wheel width, offset and tire size all determine the way a particular wheel/tire combination will work on a given car. Offset also affects the scrub radius
Scrub radius
The scrub radius is the distance in front view between the king pin axis and the center of the contact patch of the wheel, where both would theoretically touch the road....
of the steering and it is advisable to stay within the limits allowed by the vehicle manufacturer. Because wheel offset changes the lever-arm length between the center of the tire and the centerline of the steering knuckle, the way bumps, road imperfections and acceleration and braking forces are translated to steering torques (bump-steer, torque-steer, etc.) will change depending on wheel offset. Likewise, the wheel bearings will see increased thrust loads if the wheel centerline is moved away from the bearing centerline.
Wheel size
Tire code
Automobile tires are described by an alphanumeric tire code or tyre code , which is generally molded into the sidewall of the tire. This code specifies the dimensions of the tire, and some of its key limitations, such as load-bearing ability, and maximum speed...
s like 225/70R14. The first number in the code (e.g., "225") represents the nominal tire width in millimeters. This is followed by the aspect ratio (e.g.,"70"), which is the height of the side wall expressed as a percentage of the nominal width. "R" stands for radial and relates to the tire construction. The final number in the code (e.g.,"14") is the rim size measured in inches. The overall circumference of the tire will increase by increasing any of the tire's specifications. For example increasing the width of the tire will also increase its circumference, because the side wall height is a proportional length. Increasing the aspect ratio will increase the height of the tire and hence the circumference.
Off-roading
Off-roading
Off-roading is a term for driving a vehicle on unsurfaced roads or tracks, made of materials such as sand, gravel, riverbeds, mud, snow, rocks, and other natural terrain.-Off-road vehicle:...
tires may use a different measurement scheme: outside diameter times(by) tread width, followed by rim size (all in inches) - for example 31x10.50R15. The size of the disc however is denoted like 8.5" X 20.0". This shall mean that the width (of thickness) of the wheel is 8.5 inches and the diameter is 20 inches.
A dub is a custom wheel that has a wheel size of 20 inches or greater; the term dub is a slang term for twenty. DUBS may have originated as an abbreviation for double-deuces, or 22 in wheels. DUB Magazine
DUB Magazine
DUB, founded in January 2000, is a North American magazine covering urban custom car culture and also features celebrities and their vehicles. The magazine also launched the DUB Magazine Custom Auto Show & Concert, a nationwide car show and concert tour that spans 16 United States cities...
, an automotive enthusiasts magazine, takes its name from the term and covers material chiefly pertaining to urban vehicles and the people that own them.
Centerbore
The centerbore of a wheel is the size of the hole in the back of the wheel that centers it over the mounting hub of the car. Some factory wheels have a centerbore that matches exactly with the hub to reduce vibration by keeping the wheel centered. Wheels with the correct centerbore to the car they will be mounted on are known as hubcentric. Hubcentric wheels take the stress off the lug nuts, reducing the job of the lug nuts to center the wheel to the car. Wheels that are not hubcentric are known as lugcentric, as the job of centering is done by the lug nuts assuming they are properly torqued down.Centerbore on aftermarket wheels must be equal to or greater than that of the hub, otherwise the wheel cannot be mounted on the car. Many aftermarket wheels come with "hubcentric rings" that lock or slide into the back of the wheel to adapt a wheel with a larger centerbore to a smaller hub. These adapters are usually made of plastic but also in aluminum.
X-factor
Caliper Clearance (X-factor): The amount of clearance built into the wheel to allow for the vehicle's disc brakeDisc brake
The disc brake or disk brake is a device for slowing or stopping the rotation of a wheel while it is in motion.A brake disc is usually made of cast iron, but may in some cases be made of composites such as reinforced carbon–carbon or ceramic matrix composites. This is connected to the wheel and/or...
and caliper assembly.
Load capacity
Load capacity is the amount of weight a wheel will carry. This number will vary depending on the number of lugs, the PCD, the material used and the type of axle the wheel is used on. A wheel used on a free rolling trailer axle will carry more weight than that same wheel used on the drive or steering axle of a vehicle. All wheels will have the load capacity stamped on the back of the wheel.GVWR
This is the Gross Vehicle Weight RatingGross vehicle weight rating
A gross vehicle weight rating is the maximum allowable total weight of a road vehicle or trailer when loaded - i.e., including the weight of the vehicle itself plus passengers, and cargo....
. In the United States this information is required to be on the vehicle's door placard. The load capacity of the total number of wheels on the vehicle combined must meet or exceed the vehicle's GVWR.
See also
- Plus sizing
- Speedometer#Error - handy tire diameter formula, using tire codeTire codeAutomobile tires are described by an alphanumeric tire code or tyre code , which is generally molded into the sidewall of the tire. This code specifies the dimensions of the tire, and some of its key limitations, such as load-bearing ability, and maximum speed...