|A bike wheel consists of a hub, spokes and a rim. A pair of wheels is often called a wheelset, especially in the context of already built, "off the shelf" performance-oriented wheels.|
Bicycle wheels fit into the frame and fork via dropouts.
The first bicycle wheels followed the traditions of carriage building by using a wooden hub with a fixed steel axle (for which the plain bearings were located in the fork ends), wooden spokes, and a shrink fitted iron tire. A typical modern wheel has a metal hub, wire tension spokes and a metal rim that locates a pneumatic tire.
Like many other integral computer parts, compatibility issues abound. For MTB bikes, be sure to get wheels that are the right size (26" or 29"), that are compatible with the type of brakes you want (rim brakes or disc brakes), and that use the type of tire you want to run (clincher or tubeless). Road bikes are less complicated with only their main issue being the tire type (tubular or clincher).
A hub is the center part of a bicycle wheel. It consists of an axle, bearings and a hub shell. It supports the spokes (usually the head, but latterly the threaded ends); this is called the head shell or flange. Most hubs have two flanges and the hub assembly can either be steel or aluminium (although composite and more exotic materials have been used). With steel hubs, the flanges are usually separate from the hub body and contain the bearings. On alloy (aluminium) hubs, the body and flanges form one unit and contain press-fitted steel bearing surfaces.
The axle is attached to dropouts
on the fork or the frame.
The axle can attach using one of the following:
- a lever and skewer that pass through a hollow axle designed to allow for installation and removal of the wheel without any tools. This is found on most modern road and mountain bikes.
- the axle is threaded and protrudes past the edges of the fork/frame. This is found on track, fixed gear, single speed, BMX and inexpensive bikes.
- the axle has a hole with threads cut into it and a bolt can be screwed into those threads. This is found on some single speed hubs, Cannondale and Lefty hubs.
- a special long axle that the fork/frame clamps onto. This is found on some free ride and downhill mountain bikes.
The bearings allow the hub shell to rotate freely about the axle. Most bicycle hubs use ball bearings. These can be further categorized into "cup and cone" and "cartridge" bearings.
A "cup and cone" hub contains loose balls that contact an adjustable 'cone' that is screwed onto the axle and a 'race' that is pressed permanently into the hub shell. Both surfaces are very smooth to allow the bearings to roll with very little friction. This type of hub can be easily disassembled for lubrication, but it must be adjusted correctly as incorrect adjustment can lead to premature wear or failure.
In a "cartridge bearing" hub, the bearing is contained in a cartridge that is shaped like a hollow cylinder where the inner surface rotates with respect to the outer surface by the use of ball bearings. The cartridge is usually pressed into the hub shell and the axle rests against the inner surface of the cartridge. The cartridge bearing itself is generally not serviceable or adjustable; instead, the cartridge is replaced in case of wear or failure.
The hub shell is the part of the hub that the spokes attach to. Usually the hub shell has a flange that extends outward from the axle. In a spoked wheel there are holes in the flange that the spokes pass through. Some wheels (like the Full Speed Ahead RD-800) have an additional flange in the center of the hub. Other (like some from Bontrager and Zipp) do not have a noticeable flange. The spokes still attach to the edge of the hub, but not through visible holes. Other wheels (like those from Velomax/Easton) have a threaded hub shell that the spokes thread into.
Some hubs have attachments for disc brakes
or form an integral part of drum brakes.
- a disc brake
comprises a circular plate or disc, called a rotor, attached to the hub that is squeezed between brake
pads mounted within a caliper that is fixed to one side of the wheel forks. The rotor can be attached in a variety of ways using bolts
or a central locking ring.
- a drum brake
has two brake
shoes that expand out into the inside of the hub shell. Rear mounted drum brakes
are often used on tandems to supplement the rear rim brake
and to give additional stopping power.
- coaster brakes
are a particular type of drum brake
which is activated by a backward pressure applied to the pedals.
The rim is an extrusion that is butted into itself to form a circle. Most rims are made of aluminum alloy, while some very high-end rims are made of carbon fiber, and some old or very low-end rims are made of steel. Rims have even been made of wood and thermoplastic.
Rims designed for use with rim brakes
provide a smooth parallel braking surface, while rims meant for use with disc brakes
or hub brakes
sometimes lack this surface.
The Westwood rim is designed for use with rod-actuated brakes,
which press against the inside surface of the rim. These rims cannot be used with caliper rim brakes.
Rims can either have a single-wall or double-wall cross section. Single-wall rims are usually less expensive and weaker or heavier; double-wall rims tend to be stronger and more expensive. Double-wall rims may have a deep profile either to reduce aerodynamic drag or for additional strength or rigidity, especially for wheels with fewer spokes.
Aluminum rims are reinforced with either steel washers, single eyelets, or double eyelets. A single eyelet reinforces the spoke hole much like a hollow rivet. A double eyelet is a cup that is riveted into both walls of a double-walled rim.
The number of spoke holes on the rim normally matches
the number of spoke holes in the hub. For a double-walled rim there are usually holes for spokes in both walls, although some factory built wheels have rim designs without holes in the wall that contacts the tire.
Some examples are Campagnolo, Shimano and Mavic road rims/wheels and Velocity and Mavic mountain bike
Most bicycle rims are clincher
rims for use with clincher tires
(also known as wired-ons or wire-ons), which have a separate airtight inner tube enclosed by the rim and the tire.
rims have hook-shaped edges to hold the bead of the tire
in place, allowing high (8–10 bar, 120–150 psi) air pressure. If the inner part of the rim where the inner tube fits has spoke holes, they must be covered by a rim tape (usually rubber, cloth, or tough plastic) to protect the inner tube.
An advantage of this system is that the inner tube can be easily accessed in the case of a leak to be patched or replaced.
Tubular or Sew-up Rims
Some rims are designed for tubular
or sew-up tires
(also known as singles in Australia), in which the tire
is sewn into a tubular
shape and then attached to the rim with an adhesive. A tubular tire
may or may not have a separate inner tube inside. Tubular tires
require more labor to repair a puncture than clincher tires.
must be removed from the rim, opened up, patched, sewn back up, then finally glued back to the rim. Clinchers
have largely replaced tubulars
for amateur racing, but tubulars
are still commonly used for indoor track racing (where the closed track makes punctures from debris less commonplace), professional road racing, and road time trials.
Advantages of this system include a decreased chance of pinch flats, as well as it can be made to operate in a wider range of tire
pressures (from 25 to 200 psi). Furthermore, when a tubular
goes flat at high speed there is a safety margin because it will not roll off the rim if it is properly glued on. Taken as a whole, the total weight of a tubular
rim and tire
is usually lighter than its clincher
equivalent. However, for all non-racing purposes the lightness advantage is somewhat offset by the need to carry at least one entire spare tubular tire
(only a patch kit or inner tube are needed if using clincher
are most popular for bicycle road racing applications. It is argued that they also provide a better road feel and are safer than clinchers
in the case of a puncture while the bicycle is traveling at high speeds, as well as for track racing where punctures are rare.
The rim is connected to the hub by several spokes under tension. The spokes on the vast majority of wheels are steel. They may be chrome-plated or zinc-plated to inhibit rust, or they may be made of stainless steel as stainless ones are much easier to true for maintenance or following damage. Plated spokes tend to eventually rust, especially where the thread enters the nipple. Butted spokes with reduced thickness of the spokes over the center section are lighter, more elastic and more aerodynamic than spokes of uniform thickness. On high end wheelsets and custom builds lighter, but more expensive titanium, carbon fiber spokes are often used. Aluminum spokes, while lighter, are not often used as they fracture or snap more easily.
At the end of each spoke is a nut, called a nipple, which is used to adjust the tension. The nipple is usually at the rim end of the spoke, but some recent designs place it at the hub end to move its weight closer to the axis of the wheel, reducing the moment of inertia. The use of aluminium nipples at the rim also reduces the moment of inertia, but they are less durable. A nipple at the rim of a wheel usually protrudes from the rim towards the center of the wheel, but in racing, wheels may be internal to the rim, which is claimed to bring a slight aerodynamic advantage.
Radially or Tangentially
With rim brake
wheels, the front spokes can be arranged radially, with one or more crossings or a mixture, such as with crows-foot pattern spokes. However, all disc brake
wheels must have spokes attached to the hub tangentially with a resulting crossing pattern, in order to transmit torque from the hub to the rim. Similarly, rear wheels almost always have some spokes tangentially attached to the hubs, with resulting crossing patterns, to transmit the torque applied to the rear hub by the drivechain out to the rim. In higher-end wheel designs, it is not uncommon for the spokes adjacent to the drivetrain to be attached tangentially while the spokes on the other side are configured radially. There are also often more spokes on the drivetrain side. This is because, due to the space occupied by the cassette,
these spokes meet the hub closer to the center of the axle than spokes on the non-drive side, thus they are under a greater amount of tension to keep the rim in the bike's plane of symmetry. It is possible for the rear wheel to be radially spoked on both sides, although this can lead to noticeable spoke "wind-up," where the hub has to twist a little before the rim is pulled along. This will happen upon both acceleration and braking, and the movement has an adverse effect on spoke life. However, the main criticism of radial wheels is that the spokes are prone to tearing out of the hub flange, as there is little metal between the spoke hole and the edge of the flange. Frequently, a number of spokes tear off a large piece of the flange, causing instant collapse of the wheel. Few hub manufacturers recommend or warranty their products for radial spoking, and hubs that are designed for such treatment need to be heavier and tougher, negating the (very small) weight saving from using this pattern. Nevertheless, some riders choose radial spoking for its striking appearance or due to the belief that there is an aerodynamic benefit, although the latter is negligible.
Traditionally, most spokes are laced in a "three cross" fashion: this means that every spoke will directly cross three other spokes from hub flange to rim. In any but the cheapest wheels, the last spoke to be crossed will be threaded behind the first spoke to improve rigidity and strength. Certain lacings may employ soldering the last crossed spokes together with copper wire. This improves rigidity very well for velodrome riding, but has become obsolete by the use of more exotic wheel and spoke materials, notably carbon fiber.
Disc wheels are designed to minimize aerodynamic drag. A full disc is usually heavier than traditional spoked wheels and can be difficult to handle when ridden with a cross wind. For this reason, discs are commonly used only on the rear wheel.
A disc wheel may simply be a fairing that clips onto a normal wheel, addressing the drag that the spokes account for by covering them. Or, the wheel itself can be an integral disc with no spokes inside. In the latter case, carbon fiber is the material of choice. A spoked wheel with a disc cover may not be legal under UCI rules because it is a non-structural fairing.
A compromise that reduces weight and improves cross wind performance has three or four wide spokes that are integral to the rim – also typically carbon fiber.
Use Mountain Bike Wheels26 inch wheel / 559 mm rim
26 inch clincher tires
(with inner tubes) are the most common wheel size for mountain bikes.
The typical 26 inch rim has a diameter of 559 mm (22.0") and an outside tire
diameter of about 26.2" (665 mm).
Increasingly, tubeless tires
are becoming more popular. Tubeless tires
are often called by the acronym UST (Universal System Tubeless). They allow the rider to run lower tire
pressures for better traction and shock absorption without risking puncturing the tube in conventional bicycle tires.
29 inch wheel / 622 mm rim
29 inch wheels are becoming more popular for mountain bikes.
Their rim diameter of 622 mm (~24.5 inch) is the same as that used on most road, hybrid and touring bicycles. The average 29" mountain bike tire
has an outside diameter of about 28.5" (724 mm). There are advantages and disadvantages associated with this change discussed in detail in the main article.
Road/Racing Bicycle Wheels
For road bicycle racing performance there are several factors that are generally considered the most important:
Semi-aerodynamic and aerodynamic wheelsets are now commonplace for road bicycles. Aluminum rims are still the most common, but carbon fiber is also becoming popular. Carbon fiber is also finding use in hub shells to reduce weight. Because of the hub's proximity to the center of rotation, reducing the hub's weight has less effect than reducing the rim's weight.
Semi-aerodynamic and aerodynamic wheelsets are characterized by greater rim depth (which is the distance between the outermost and the innermost surfaces of the rim); a triangular or pyramidal cross-section; fewer numbers of spokes (or no spokes at all); and with blades
molded of composite material supporting the rim.
The spokes are also often flattened in the rotational direction to reduce wind drag. These are called bladed spokes. However, semi-aerodynamic and aerodynamic wheelsets tend to be heavier than more traditional spoked wheelsets due to the extra shapings of the rims and spokes. More important, the rims must be heavier when there are fewer spokes, as the unsupported span between spokes is greater. While the increase in weight is somewhat important, it is the increased rotating inertia that is the greater problem for "aero" wheels, as the rim, being farther from the axis of rotation, has the largest effect on rotational inertia. Or in other words: moving 20 grams from the spokes (fewer spokes) to the rim will keep the weight the same, but will increase the rotational inertia. (But concerns about rotational inertia of bicycle wheels are vastly overstated--the inertia of all bicycle wheels is negligible compared to the mass of the rider.)
"Aero" wheels are also reputedly more difficult to control in a "cross-wind" condition due to the larger projected lateral area. The trade off between rim depth, weight and spoke count is still under debate. However, a number of wheel manufacturers are now producing wheels with roughly half the spokes of a top of the line traditional wheel from the 1980's, with approximately the same rotational inertia and less total weight. These improvements have been made possible primarily through improved aluminum alloys for the rims.
Almost all clincher
carbon fiber wheelsets, such as those made by Zipp and Mavic, still use aluminum parts at the clinching part of the rim. Exceptions to this are the Campagnolo Hyperon Ultra Clincher,
Bontrager Race XXX Lite Carbon Clincher,
DT Swiss RRC1250, and Lightweight Standard C wheelsets, in which the rims are entirely made from carbon fiber.
Touring Bicycle Wheels
Touring bicycles may have wheels similar to road machines or similar to mountain bikes
depending upon the terrain to be traveled, but they are built for strength, as heavy loads may be carried. Lightest possible weight and optimum aerodynamic performance is not required.
Technical aspects Sizes
Bicycle rims and tires
come in many different types and sizes. The International Organization for Standardization (ISO) and the European Tire
and Rim Technical Organization (ETRTO) define a modern, unambiguous system of sizing designations and measurement procedures for different types of tires
and rims in international standard ISO 5775. For example:
- For wired-edge tires,
the ISO designation lists the width of the inflated tire
and the diameter of which the tire
sits on the rim (both in millimeters and separated by a hyphen, such as 37-622).
- For beaded-edge tires,
the ISO designation lists an overall diameter code (16, 18, 20, 22, 24, or 26) and a width code (1.25, 1.375, 1.75, or 2.125), defined by measurement tables given in the standard and separated by a cross: 20×1.375
* For rims, the ISO designation lists the rim diameter (where the tire
sits) and the rim's inner width, both in millimeters and separated by a cross, along with a letter code for the rim type (e.g., "C" = Crotchet-type): 622x19C
In practice, most tires
(and inner tubes) sold today carry some historic size markings apart from the modern ISO 5775-1 designation, for which there no longer exists any officially maintained definition, but which are still widely used colloquially:
- an old French tire
designation that was based on the approximate, crudely rounded, outer diameter of the inflated tire
in millimeters: 700×35 C
- an old British inch-based designation: 28 × 1 5/8 × 1 3/8
Which designation is most popular varies with region and type of bicycle. For a comprehensive equivalence table between old and new markings, see the ISO 5775 article, the table in Annex A of the ISO 5772 standard, as well as Tire Sizing
by Sheldon Brown.
Most road and racing bicycles use 622mm rims. Many mountain bikes
use either 26 inch wheels or 29 inch wheels. Some bicycles designed for triathlon or time trial purposes use 650c wheels. BMX bikes typically use 20 inch wheels, and some use 24 inch wheels.
The 650C triathlon size has the ISO diameter size of 571 mm. Size 650B is 584 mm and 650A is 590 mm.
Kids' bikes can have rim diameters ranging from 239 mm (12 × 1 3/8 × 1 1/4) to 400 mm (18 × 1 1/4). Older bikes may have, for example, 630 mm (27 × 1 1/4) or 597 mm (26 × 1 1/4) wheels that are incompatible with any of the sizes commonly used today.
Wheel rims also come in a variety of widths. High performance road racing rims are usually narrow, 18 mm or so, and less performance oriented rims may be 24 mm wide or more.
Smaller wheels, all else being equal, have higher rolling resistance
than larger wheels. "Rolling resistance increases in near proportion as wheel diameter is decreased for a given constant inflation
pressure." An Oldenburg University's bicycle research group found that Schwalbe Standard GW HS 159 tires
have a Crr of 455 for the ISO size 47-406 (20 in x 1.5 in) and, for the same model tire,
a Crr of 336 for the ISO size 37-622 (700c) have a size to resistance ratio of about -1.8.
also is reduced with increasing tire
pressure, although the reduction is slightly above 100 psi. While thinner bicycle tires
are lighter and have less wind resistance, they actually have slightly higher rolling resistance
than slightly larger tires
at the same pressure.
Reaction to Load
A load applied at the hub causes the wheel to flatten slightly near the ground contact area. The rest of the wheel remains approximately circular. The tension in all of the spokes is increased except for the few in the flat spot.
However, when a radial load is applied to a wheel at the hub (i.e. by a rider sitting on the bicycle), the tension of all the spokes does not increase significantly, with only the spokes directly under the hub decreasing their tension.
Due to the fact that wheels rotate and translate (move in a straight line) when a bicycle moves, more force is required to accelerate a unit of mass on the wheel than on the frame.
It is not the center of gravity (mass) that matters, but the moment of inertia, which takes the rotation into account. Reducing the rotational inertia can be achieved by moving the spoke nipples to the hub or using lighter nipples such as aluminum. This can be pictured by imagining an ice skater spinning, when they pull in their arms, they rotate more quickly. A rule of thumb in the case of acceleration only, is "the effect of a given mass on the wheels is almost twice that of the same mass on the frame." But again, the distinction between rotating and non-rotating mass is only felt during acceleration (and braking to a lesser extent), and mass at the hub matters a lot less than mass at the rim. See Bicycle weight and power for more detail.
Due to the need to mount multiple drive-train sprockets
and disk brake
rotors usually to only one side of a hub, and the need to have the rim be centered with respect to the frame
or fork, spokes may be asymmetrical with shorter and usually higher-tension spokes on the side with the additional components. This is referred to as dish. There are special tools, called dishing gauges, which indicate whether or not a rim is centrally positioned with the correct amount of dish.
Several different techniques have been tried to minimize dish. These include moving both hub flanges inboard the same amount, and/or placing spoke holes asymmetrically in the rim.