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The first bicycle wheels followed the traditions of carriage building: a wooden hub, a fixed steel axle (the 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 or carbon fiber rim which holds a pneumatic rubber tire.
A hub is the center part of a bicycle wheel. It consists of an axle, bearings and a hub shell. The hub shell typically has two machined metal flanges to which spokes can be attached. Hub shells can be one-piece with press-in cartridge or free bearings or, in the case of older designs, the flanges may be affixed to a separate hub shell.
The axle is attached to dropouts on the fork or the frame. The axle can attach using a
- Quick release - a lever and skewer that pass through a hollow axle designed to allow for installation and removal of the wheel without any tools (found on most modern road bikes and some mountain bikes).
- Nut - the axle is threaded and protrudes past the sides of the fork/frame. (often found on track, fixed gear, single speed, BMX and inexpensive bikes)
- bolt - the axle has a hole with threads cut into it and a bolt can be screwed into those threads. (found on some single speed hubs, Cannondale Lefty hubs)
- Thru axle - a long axle, typically 20 mm (110 mm width), [they can be 9 mm (100.33 mm width) in diameter for durability], onto which the fork/frame clamps (found on most mountain bike forks).
- Female axle - hollow center axle, typically 14, 17, or 20 mm in diameter made of chromoly and aluminum, with two bolts thread into on either side. This design can be much stronger than traditional axles, which are commonly only 8 mm, 9 mm, 9.5 mm, or 10 mm in diameter. (found on higher end BMX hubs and some mountain bike hubs)
Modern[when?] bicycles have adopted standard axle spacing: the hubs of front wheels are generally 100 mm wide fork spacing, road wheels with freehubs generally have a 130 mm wide rear wheel hub. Mountain bikes have adopted a 135 mm rear hub width, which allows clearance to mount a brake disc on the hub or to decrease the wheel dish for a more durable wheel. Freeride and downhill are available with 150 mm spacing.
The bearings allow the hub shell (and the rest of the wheel parts) to rotate freely about the axle. Most bicycle hubs use steel or ceramic ball bearings. Older designs used "cup and cone", whereas some modern wheels use pre-assembled "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 smooth to allow the bearings to roll with little friction. This type of hub can be easily disassembled for lubrication, but it must be adjusted correctly; incorrect adjustment can lead to premature wear or failure.
In a "cartridge bearing" hub, the bearings are 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 manufacturing tolerances, as well as seal quality, can be significantly superior to loose ball bearings. The cartridge is pressed into the hub shell and the axle rests against the inner race of the cartridge. The cartridge bearing itself is generally not serviceable or adjustable; instead the entire cartridge bearing is replaced in case of wear or failure.
Hub shell and flanges 
The hub shell is the part of the hub to which the spokes (or disc structure) attach. The hub shell of a spoked wheel generally has two flanges extending radially outward from the axle. Each flange has holes or slots to which spokes are affixed. Some wheels (like the Full Speed Ahead RD-800) have an additional flange in the center of the hub. Others (like the 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.
On traditionally-spoked wheels, flange spacing effects the lateral stiffness of the wheel, with wider being stiffer, and flange diameter effects the torsional stiffness of the wheel and the number of spoke holes that the hub can accept, with larger diameter being stiffer and accepting more holes. Asymmetrical flange diameters, tried to mitigate the adverse effects of asymmetrical spacing and dish necessary on rear wheels with many sprockets, have also been with modest benefits.
Hub brakes 
Some hubs have attachments for disc brakes or form an integral part of drum brakes.
- Disc brakes - a disc brake comprises circular plate or disc attached to the hub which is squeezed between brake pads mounted within a caliper that is fixed to one side of the wheel forks. The brake disc can be attached in a variety of ways using bolts or a central locking ring.
- Drum brakes - 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 give additional stopping power.
- Coaster brake - coaster brakes are a particular type of drum brake which is actuated by a backward pressure applied to the pedals. The mechanism is contained inside the bicycle wheel hub shell.
For information on other types of bicycle brakes see the full article on bicycle brake systems.
The rear hub has one or more methods for attaching a gear to it.
- Freehub - The mechanism that allows the rider to coast is built into the hub. Splines on the freehub body allow a single sprocket or, more commonly, a cassette containing several sprockets to be slid on. A lock ring then holds the cog(s) in place. This is the case for most modern bicycles.
- Freewheel - The mechanism that allows the rider to coast is not part of the hub, it is contained in a separate freewheel body. The hub has threads that allow the freewheel body to be screwed on, and the freewheel body has threads and/or splines for fitting sprockets, or in the case of most single speed freewheels an integral sprocket. This style of hub was used before the freehub became practical.
- Track sprocket - There is no mechanism that allows the rider to coast. There are two sets of threads on the hub shell. The threads are in opposite directions. The inner (clockwise) set of threads is for a track sprocket and the outer (counter-clockwise) set is for a reverse threaded lock ring. The reverse threads on the lock ring keep the sprocket from unscrewing from the hub, which is otherwise possible when slowing down.
- Flip-flop hub - Both sides of the hub are threaded, allowing the wheel to be removed and reversed in order to change which gear is used. Depending on the style of threads, may be used with either a single speed freewheel or a track sprocket.
- Internal geared hub - the mechanism to provide multiple gear-ratios is contained inside the shell of the hub. Many bicycles with three-speed internally geared hubs were built in the last century. This is an extremely robust design, although much heavier than more modern designs of multi-gear-ratio arrangements. Modern hubs are available from three-speed to 14 speeds or a continuously variable transmission hub, in the case of the NuVinci.
The rim is commonly a metal extrusion that is butted into itself to form a hoop, though may also be a structure of carbon fiber composite, and was historically made of wood. Some wheels use both an aerodynamic carbon hoop bonded to an aluminum rim on which to mount conventional bicycle tires.
Metallic bicycle rims are now normally made of aluminium alloy, although until the 1980s most bicycle rims - with the exception of those used on racing bicycles - were made of steel and thermoplastic.
The Westwood pattern rim was one of the first rim designs, and rod-actuated brakes, which press against the inside surface of the rim were designed for this rim. These rims cannot be used with caliper rim brakes.
The cross-section of a rim can have a wide range of geometry, each optimized for particular performance goals. Aerodynamics, mass and inertia, stiffness, durability, tubeless tire compatibility, brake compatibility, and cost are all considerations. If the part of the cross-section of the rim is hollow where the spokes attached, as in the Sprint rim pictured, it is described as box-section or double-wall to distinguish it from single-wall rims such as the Westwood rim pictured. The double wall can make the rim stiffer. Triple-wall rims have additional reinforcement inside the box-section.
Aluminum rims are often reinforced with either single eyelets or double eyelets to distribute the stress of the spoke. 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.
Clincher rims 
Most bicycle rims are "clincher" rims for use with clincher tires. These tires have a wire or aramid (Kevlar or Twaron) fiber bead that interlocks with flanges in the rim. A separate airtight inner tube enclosed by the rim supports the tire carcass and maintains the bead lock. If the inner part of the rim where the inner tube fits has spoke holes, they must be covered by a rim tape or strip, 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.
The ISO 5775-2 standard defines designations for bicycle rims. It distinguishes between
- Straight-side (SS) rims
- Crochet-type (C) rims
- Hooked-bead (HB) rims
Traditional clincher rims were straight-sided. Various "hook" (also called "crochet") designs emerged in the 1970s to hold the bead of the tire in place, allowing high (6–10 bar, 80–150 psi) air pressure.
Tubular or sew-up rims 
Some rims are designed for tubular tyres which are torus shaped and attached to the rim with adhesive. The rim provides a shallow circular outer cross section in which the tire lies instead of flanges on which tire beads seat.
A tubeless tire system requires an airtight rim — capable of being sealed at the valve stem, spoke holes (if they go all the way through the rim) and the tire bead seat — and a compatible tire. Universal System Tubeless (UST), originally developed by Mavic, Michelin and Hutchinson for mountain bikes is the most common system of tubeless tires/rims for bicycles. The main benefit of tubeless tires is the ability to use low air pressure for better traction without getting pinch flats because there is no tube to pinch between the rim and an obstacle.
Some cyclists have avoided the price premium for a tubeless system by sealing the spoke holes with a special rim strip and then sealing the valve stem and bead seat with a latex sealer. However, tires not designed for tubeless application do not have as robust a sidewall as those that are.
The drawbacks to tubeless tires are that they are notorious for being harder to mount on the rim than clincher tires, and that the cyclist must still carry a spare tube to insert in case of a flat tire due to a puncture.
The rim is connected to the hub by several spokes under tension. Original bicycle wheels used wooden spokes that could be loaded only in compression, modern bicycle wheels almost exclusively use spokes that can only be loaded in tension. There are a few companies making wheels with spokes that are used in both compression and tension.
One end of each spoke is threaded for a specialized nut, called a nipple, which is used to connect the spoke to the rim and adjust the tension in the spoke. This is normally at the rim end. The hub end normally has a 90 degree bend to pass through the spoke hole in the hub, and a head so it does not slip through the hole.
Double-butted spokes have reduced thickness over the center section and are lighter, more elastic, and more aerodynamic than spokes of uniform thickness. Single-butted spokes are thicker at the hub and then taper to a thinner section all the way to the threads at the rim. Triple-butted spokes also exist and are thickest at the hub, thinner at the threaded end, and thinnest in the middle.
Apart from tubeless wheels, which do not need them, tubed bicycle wheels require rim tapes or strips, a flexible but tough liner strip (usually rubber or woven nylon or similar material) attached to the inner circumference of the wheel to cover the ends of the nipples. Otherwise, the nipple ends wear a hole in the tube causing a flat tire.
In 2007, Mavic introduced their R-Sys, a new bicycle spoke technology that allows the spokes to be loaded in both tension and compression. This technology is promised to allow for fewer spokes, lower wheel weight and inertia, increased wheel stiffness, with no loss of durability. However, in 2009 Mavic recalled R-Sys front wheels due to spoke failures leading to collapse of the entire wheel.
Cross section 
Spokes are usually circular in cross-section, but high-performance wheels may use spokes of flat or oval cross-section, also known as bladed, to reduce aerodynamic drag. Some spokes are hollow tubes.
The spokes on the vast majority of modern bicycle wheels are steel or stainless steel. Stainless steel spokes are favored by most manufacturers and riders for their durability, stiffness, damage tolerance, and ease of maintenance. Spokes are also available in titanium, aluminum, or carbon fiber.
Number of spokes 
Conventional metallic bicycle wheels for single rider bikes commonly have 28, 32 or 36 spokes, while wheels on tandems have as many as 40 or 48 spokes to support the weight of an additional rider. BMX bikes commonly have 36 or 48 spoke wheels. Lowrider bicycles may have as many as 144 spokes per wheel. Wheels with fewer spokes have an aerodynamic advantage, as the aerodynamic drag from the spokes is reduced. On the other hand, the reduced number of spokes results in a larger section of the rim being unsupported, necessitating stronger and often heavier rims. Some wheel designs also locate the spokes unequally into the rim, which requires a stiff rim hoop and correct tension of the spokes. Conventional wheels with spokes distributed evenly across the circumference of the rim are considered more durable and forgiving to poor maintenance. The more general trend in wheel design suggests technological advancement in rim materials may result in further reduction in the number of spokes per wheel.
Lacing is the process of threading spokes through holes in the hub and rim so that they form a spoke pattern. While most manufacturers use the same lacing pattern on both left and right sides of a wheel, it is becoming increasingly common to find specialty wheels with different lacing patterns on each side. A spoke can connect the hub to the rim in a radial fashion, which creates the lightest and most aerodynamic wheel. However, to efficiently transfer torque from the hub to the rim, as with driven wheels or wheels with drum or disc brakes, durability dictates that spokes be mounted at an angle to the hub flange up to a "tangential lacing pattern" to achieve maximum torque capability (but minimum vertical wheel stiffness). Names for various lacing patterns are commonly referenced to the number of spokes that any one spoke crosses. Conventionally laced 36- or 32-spoke wheels are most commonly built as a cross-3 or a cross-2, however other cross-numbers are also possible. The angle at which the spoke interfaces the hub is not solely determined by the cross-number; as spoke count and hub diameter will lead to significantly different spoke angles. For all common tension-spoke wheels with crossed spokes, a torque applied to the hub will result in one half of the spokes - called "leading spokes" tensioned to drive the rim, while other half - "trailing spokes" are tensioned only to counteract the leading spokes. When forward torque is applied (i.e., during acceleration ), the trailing spokes experience a higher tension, while leading spokes are relieved, thus forcing the rim to rotate. While braking, leading spokes tighten and trailing spokes are relieved. The wheel can thus transfer the hub torque in either direction with the least amount of change in spoke tension, allowing the wheel to stay true while torque is applied.
Wheels that are not required to transfer any significant amount of torque from the hub to the rim are often laced radially. Here, the spokes leave the hub at perpendicular to the axle and go straight to the rim, without crossing any other spokes - e.g., "cross-0". This lacing pattern can not transfer torque as efficiently as tangential lacing. Thus it is generally preferred to build a crossed-spoke wheel where braking and drive forces are present. Hubs that have previously been laced in any other pattern should not be used for radial lacing, as the pits and dents created by the spokes can be the weak points along which the hub flange may break. This is not always the case: for example if the hub used has harder, steel flanges like those on a vintage bicycle.
Wheel builders also employ other exotic spoke lacing patterns (such as "crow's foot", which is essentially a mix of radial and tangential lacing) as well as innovative hub geometries. Most of these designs take advantage of new high-strength materials or manufacturing methods to improve wheel performance. As with any structure, however, practical usefulness is not always agreed, and often nonstandard wheel designs may be opted for solely for aesthetic reasons.
Adjustment ("truing") 
There are three aspects of wheel geometry which must be brought into adjustment in order to true a wheel. "Lateral truing" refers to elimination of local deviations of the rim to the left or right of center. "Vertical truing" refers to adjustments of local deviations (known as hop) of the radius, the distance from the rim to the center of the hub. "Dish" refers to the left-right centering of the plane of the rim between the lock nuts on the outside ends of the axle. This plane is itself determined as an average of local deviations in the lateral truing. For most rim-brake bicycles, the dish will be symmetrical on the front wheel. However, on the rear wheel, because most bicycles accommodate a rear sprocket (or group of them), the dishing will often be asymmetrical: it will be dished at a deeper angle on the non-drive side than on the drive side.
In addition to the three geometrical aspects of truing, the overall tension of the spokes is significant to the wheel's fatigue durability, stiffness, and ability to absorb shock. Too little tension leads to a rim that is easily deformed by impact with rough terrain. Too much tension leads to overstressed spokes which have a short life. Spoke tensiometers are tools which measure the tension in a spoke. Another common method for making rough estimates of spoke tension involves plucking the spokes and listening to the audible tone of the vibrating spoke. The optimum tension depends on the spoke length and spoke gauge (diameter). Tables are available online which list tensions for each spoke length, either in terms of absolute physical tension, or notes on the musical scale which coincide with the approximate tension to which the spoke should be tuned. It should be noted that in the real world, a properly trued wheel will not, in general, have a uniform tension across all spokes, due to variation among the parts from which the wheel is made.
Finally, for best, long-lasting results, spoke wind-up should be minimized. When a nipple turns, it twists the spoke at first, until there is enough torsional stress in the spoke to overcome the friction in the threads between the spoke and the nipple. This is easiest to see with bladed or ovalized spokes, but occurs in round spokes as well. If a wheel is ridden with this torsional stress left in the spokes, they may untwist and cause the wheel to become out of true. Bladed and ovalized spokes may be held straight with an appropriate tool as the nipple is turned. The common practice for minimizing wind-up in round spokes is to turn the nipple past the desired orientation by about a quarter turn, and then turn it back that quarter turn.
In wheel truing, all these factors must be incrementally brought into balance against each other. A commonly recommended practice is to find the worst spot on the wheel, and bring it slightly more into true before moving on to the next worst spot on the wheel.
"Truing stands" are mechanical devices for mounting wheels and truing them. It is also possible to true a wheel while it is mounted on the bike: brake pads or some other fixed point may be used as a reference mark, however this is less accurate.
At one end of each spoke is a specialized nut, called a nipple, which is used to connect the spoke to the rim and adjust the tension in the spoke. The nipple is usually located at the rim end of the spoke but on some wheels is at the hub end to move its weight closer to the axis of the wheel, reducing the moment of inertia.
Until recently[when?] there were only two types of nipples: brass and aluminum (often referred to as "alloy"). Brass nipples are heavier than aluminum, but they are more durable. Aluminium nipples save weight, but they are less durable than brass and more likely to corrode.
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, offering a slight[quantify] aerodynamic advantage.
A wheel can be formed in one piece from a material such as thermoplastic (glass-filled nylon in this case) or carbon fiber. The former are commonly used for inexpensive BMX wheels and have a maximum tire pressure of 45 psi (3bars or atmospheres). The latter may be used for high-end aerodynamic racing wheels.
Disc wheels 
Disc wheels are designed to minimize aerodynamic drag. A full disc is usually heavier than traditional spoke wheels, and can be difficult to handle when ridden with a cross wind. For this reason, international cycling organizations often ban disc wheels or limit their use to the rear wheel of a bicycle. However, international triathlon federations were (and are still) less restrictive and is what led to the wheels' initial usage growth in popularity in the 1980s.
A disc wheel may simply be a fairing that clips onto a traditional, spoke wheel, addressing the drag that the spokes generate by covering them; or the disc can be integral to the wheel with no spokes inside. In the latter case carbon fiber is the material of choice. A spoke wheel with a disc cover may not be legal under UCI Union Cycliste Internationale rules because it is a non-structural fairing but are again acceptable under ITU International Triathlon Union rules.
A compromise that reduces weight and improves cross wind performance has a small number (three or four) tension-compression spokes molded integral to the rim – also typically carbon fiber.
|This section does not cite any references or sources. (January 2013)|
Bicycle wheels can be categorized by their primary use.
Road/racing bicycle wheels 
- rotational inertia
- hub/bearing smoothness
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; however, because of the hub's proximity to the center of rotation reducing the hub's weight has less inertial effect than reducing the rim's weight.
Semi-aerodynamic[clarification needed] and aerodynamic wheelsets are characterized by greater rim depth, which is the radial distance between the outermost and the innermost surfaces of the rim; a triangular or pyramidal cross-section; and by fewer numbers of spokes, or no spokes at all—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. A number of wheel manufacturers are now producing wheels with roughly half the spokes of the highest performance traditional wheel from the 1980s, with approximately the same rotational inertia and less total weight. These improvements have been made possible primarily through improved aluminium alloys for the rims.[original research?]
Most clincher carbon fiber wheelsets, such as those made by Zipp and Mavic, still use aluminum parts at the clinching part of the rim. An increased number of all-carbon rims, such as Campagnolo Hyperon Ultra Clincher, Viva v8 wheels, Bontrager's Carbon Clincher wheels, DT Swiss RRC1250, Corima Winium and Aero (also tubeless, see below) and Lightweight Standard C wheelsets are now available.
French tire manufacturer Hutchinson has introduced a tubeless wheel system, Road Tubeless, that shares many similarities to the UST (Universal System Tubeless) that was developed in conjunction with Mavic and Michelin. Road Tubeless rims, like UST rims, have no spoke holes protruding to the air chamber of the rim. The flange of the Road Tubeless rim is similar to the hook bead of a standard clincher rim but is contoured to very close tolerances to interlock with a Road Tubeless tire, creating an airtight seal between tire and rim. This system eliminates the need for a rim strip and inner tube.
700C road bicycle wheels / ISO 622mm 
Touring, race, and cyclo-cross bicycles may have vastly different design goals for their wheels. The lightest possible weight and optimum aerodynamic performance are beneficial for road bicycles, while for cyclo-cross strength gains importance, and for touring bicycles strength becomes even more important. However this diameter of rim, identical in diameter to the "29er" rim, is by far the most common on these styles of bicycles. It rolls more easily than smaller diameter tires. Road wheels may be designed for tubular or clincher tires, commonly referred to as "700C" tires.
Mountain bike wheels 
Mountain bike wheels are described by the approximate outer diameter of the wheel plus a wide, ~2 inch tire.
26 inch / ISO 559mm 
26-inch clincher tires (with inner tubes) are the most common wheel size for mountain bikes. This tradition was started initially because the early mountain bike pioneers procured the wheels for their early bikes from American-made bicycles rather than the larger European standards in use. 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 common are tubeless tires conforming to the UST (Universal System Tubeless) standard pioneered by French wheel manufacturer Mavic in conjunction with tire manufacturers Hutchinson and Michelin.
27.5 inch / ISO 584mm / 650B 
27.5-inch mountain bike wheels (which some also refer to as 650B) use a rim that has a diameter of 584 mm (23.0") with wide, knobby tires (~27.5 x 2.3 / ISO 58-584) are approximately the midway point between the 26-inch (ISO-559mm) and the 29-inch (ISO-622mm) standards. They carry some of the advantages of both formats, with a smoother ride than a 26 inch wheel and more stiffness and durability than a 29" wheel. As 27.5-inch wheels have just started to be embraced by larger manufacturers, one of the primary disadvantages has been a reduced selection of compatible frames and forks. However, an increased availability of 27.5-inch forks, wheels, tires and tubes is expected in 2013.
29 inch / ISO 622mm / 700C 
“29-inch wheels”, which also conform to the popular 700C (622 mm diameter clincher) wheel standard are becoming more popular for not only cyclocross bikes but also cross-country mountain bikes. Their rim diameter of 622 mm (~24.5 inch) is identical to most road, hybrid, and touring bicycle wheels, but are typically reinforced for greater durability in off-road riding. The average 29-inch mountain bike tire has an outside diameter of about 28.5" (724 mm).
BMX / 20 inch / ISO 406 mm 
Usually 20 inches in diameter (rim diameter of 406 mm), BMX (bicycle motocross) wheels are small for several reasons: they are suitable for young and small riders; their lower cost is compatible with inexpensive bicycles; the size makes them stronger to withstand the additional loads generated by BMX jumps and stunts; and to reduce rotational inertia for easier wheel acceleration.
Technical aspects 
Bicycle rims and tires came in many different types and sizes before efforts were made to standardize and improve wheel/tire compatibility. The International Organization for Standardization (ISO) and the European Tyre and Rim Technical Organisation (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 with which the tire sits on the rim, both in millimeters and separated by a hyphen: 37-622
- 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" = Crochet-type): 622x19C
In practice, most tires (and inner tubes) sold today carry apart from the modern ISO 5775-1 designation also some historic size markings, for which no officially maintained definition currently exists, but which are still widely used:
- an old French tire designation that was based on the approximate outer diameter of the inflated tire in millimeters: 700×35 C.
- an old British inch-based designation: 597 mm (26 × 1¼), 590 mm (26 × 1⅜, which is the most common), 630 mm (27 × 1¼), and 635 mm (28 × 1½)
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 today use 622 mm diameter (700C) rims, though 650C rims are popular with smaller riders and triathletes. The 650C size has the ISO diameter size of 571 mm. Size 650B is 584 mm and 650A is 590 mm. 650B is being promoted as a 'best of both worlds' size for mountain biking. Most adult mountain bikes use “26 inch” wheels. Smaller youth mountain bikes use 24 inch wheels. The larger 700C (29 inch) wheels have enjoyed some recent popularity amongst off-road bicycle manufacturers. The formerly popular (27 inch) wheel size is now rare. These rims are slightly larger in diameter than 700C wheels and are non-compatible with bicycle frames and tires designed for the 700C standard.
Children's bicycles are commonly sized primarily based on wheel diameter rather than seat tube length (along the rider's inseam) dimension. Thus, a wide range of small bike wheels are still found, ranging from 239 mm (12 inches) diameter to 400 mm (18 inches).
Wheel rims also come in a variety of widths to provide optimum performance for different uses. High performance road racing rims are narrow, 18 mm or so. Wider touring or durable off-road tires require rims of 24 mm wide or more.
Other sizes 26" 
The common "26-inch" wheel used on mountain bikes is an American size using a 559 mm rim, traditionally with hooked edges.
- 650 - ISO 32-597 (26 x 1 ¼) - Older British sport bikes. Schwinns with narrow tires.
- 650A - ISO 37-590 (26 x 1 ⅜) - Common on many vintage frames ranging from American-made Murray and Huffy as well as English and French manufactures like Raleigh and Peugeot.
- 650B - ISO 40-584 (26 x 1 ½) - Also 650B demi-ballon. French tandems, touring bicycles; enjoying a revival. (584 mm rims with wide, knobby tires, aka; baloon, are also known as 27.5 inch mountain bike wheels)
- 650C - ISO 44-571 (26 x 1 ¾) - Formerly 47mm wide on Schwinn cruisers and for British trade/delivery bikes. Currently ISO 28-571, size is the same, but the narrower and less overall wheel diameter are built for triathlon, time trial and small road bikes.
Rolling resistance 
There are a number of variables that determine rolling resistance: tire tread, width, diameter, tire construction, tube type (if applicable), and pressure are all important.
Smaller diameter 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."
Reaction to load (tensioned wire spoked wheels) 
The reaction to a radial load of a well-tensioned wire spoked wheel, such as by a rider sitting on a bicycle, is that the wheel flattens slightly near the ground contact area. The rest of the wheel remains approximately circular. The tension of all the spokes do not increase significantly. Instead, only the spokes directly under the hub decrease their tension. The issue of how best to describe this situation is debated. Some authors conclude from this that the hub "stands" on those spokes immediately below it that experience a reduction in tension. Other authors conclude that the hub "hangs" from those spokes above it that have higher tension than the ones below it.
Despite being composed of thin and relatively flexible spokes, wire wheels are radially stiff and provide very little suspension compliance compared to even high-pressure bicycle tires.
Rotating mass 
Due to the fact that wheels rotate as well as 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. To accelerate a wheel, total wheel mass matters less than the moment of inertia, which describes the inertial effect of the mass resisting acceleration (inertia) based on its location with respect to the axis of rotation (the center of the wheel hub/axle). In wheel design, reducing the rotational inertia has the benefit of more responsive, faster-accelerating wheels. To accomplish this, wheel designs are employing lighter rim materials, moving the spoke nipples to the hub or using lighter nipples such as aluminum. Note however that rotational inertia is only a factor during acceleration (and deceleration/braking). At constant speed, aerodynamics are a significant factor. For climbing, total mass remains important. See Bicycle performance for more detail.
The hub flanges of modern tension-spoked bicycle wheels are always spaced wider than where the spokes attach to the rim. When viewed in cross section, the spokes and hub form a triangle, a structure that is stiff both vertically and laterally. In three dimensions, if the spokes were covered, they would form two cones or "dishes". The greater the separation between the hub flanges, the deeper the dishes, and the stiffer and stronger the wheel can be laterally. The more vertical the spokes, the shallower the dish, and the less stiff the wheel will be laterally.
The dishes on each side of a wheel are not always equal. The cogset (freewheel or cassette) of a rear wheel and disc brake rotors, if installed, takes up width on the hub, and so the flanges may not be located symmetrically about the center plane of the hub or the bike. Since the rim must be centered, but the hub flanges are not, there is a difference in dish between the two sides. Such an asymmetrical wheel is called a "dished" wheel. The side of the wheel with less dish has slightly shorter but significantly higher-tensioned spokes than side with more dish. Several different techniques have been tried to minimize this spoke asymmetry. In addition to modified hub geometry, some rims have off-center spoke holes, and the mounting of common J-bend spokes at the hub flange can be altered "inboard" or "outboard".
A truing stand or a dishing gauge, can be used to measure the position of the rim relative to the hub. Thus "dishing" is also used to describe the process of centering the rim on the hub, even in the case of symmetrical wheels.
See also 
- Saris (March 8, 2012). "Shadow Conspiracy Releases Axle Conversion Kit". BikeBoardMedia, Inc. Retrieved 2013-01-25. "the female axle will be lighter and stronger. This is because when the width of the axle is reduced, weight is shaved, and less leverage is applied on the axle during peg tricks."
- "Hub Axles". 01/05/2013. Retrieved 2013-01-25. "you'll need to "re-dish" the wheel, by pulling the rim to the right. ... The downside of this is that pulling the rim to the right increases the tension difference between the left and right spokes, resulting in a somewhat weaker wheel."
- Sheldon Brown and John Allen. "Bicycle Frame/Hub Spacing". Retrieved 2013-01-25. "Diameter. Common diameters include 8 mm, 9 mm, 9.5 mm and 10 mm, 5/16" and 3/8" (3/8" is generally interchangeable with 9.5 mm)."
- Gary Boulanger (Thursday, Jul 19, 2007). "NEW: Chris King 150mm DH/freeride hub". BikeRadar.com. Retrieved 2013-01-25.
- Jobst Brandt (1993). The Bicycle Wheel (3rd ed.). Avocet. pp. 59–64. "The distance between flanges gives a wheel its lateral strength. Wheels with narrow flange spacing and many gears are less suited to rough roads than those with wider spacing and fewer gears. Large-flange hubs provide no functional advantage and have the disadvantage of added weight. Aggressively ridden tandem bicycle are an exception."
- "Rohloff SPEEDHUB 500/14". Rohloff AG. Retrieved 2010-03-16.
- "NuVinci transmission". Fallbrook Technologies Inc. Archived from the original on 2 April 2010. Retrieved 2010-03-16.
- Brown, Sheldon. "Sheldon Brown's Bicycle Glossary W: Wooden Rims". Sheldon Brown. Archived from the original on 11 January 2008. Retrieved 2008-01-22.
- "Glossary of Bicycle Wheel Terms". Bromley Bike Co. Retrieved 2011-08-02.
- "ISO/E.T.R.T.O. 630 mm, Note on tire/rim compatibility". Archived from the original on 22 June 2008. Retrieved 2008-05-23.
- "Mistral Demystified: Development of the AM 17" rim". Retrieved 2008-05-23.
- Felton, Vernon. "Are Tubeless Tires Worth It?". Archived from the original on 16 January 2009. Retrieved 2009-01-16.
- Brown, Sheldon. "Sheldon Brown's Glossary: U. S. T". Sheldon Brown. Archived from the original on 29 January 2009. Retrieved 2009-01-16.
- Phillips, Matt (December 2008). "The Scoop on Tubeless". Bicycling (Rodale): 90.
- "Mavic TraComp Tech". Retrieved 2011-04-28.
- Sheldon Brown. "Wheelbuilding". Retrieved 2010-03-22.
- "Tech Specs Spokes". DT Swiss. Retrieved 2012-05-31.
- "Mavic Announces R-SYS Recall". VeloNews. January 8, 2009. Retrieved 2010-03-22.
- Sheldon Brown and John Allen (November 5, 2011). "Spokes". Retrieved 2013-01-26.
- Caley Fretz (Sep. 27, 2011). "Zircal aluminum spokes". VeloNews. Retrieved 2013-01-26.
- Jessica Lopez (November, 2010). "Custom Bicycles - Joker's Bike Club". Lowrider Bicycle Magazine. Retrieved 2013-01-24. "144-spoke wheels mounted onto 20x1.75 Kendras"
- Nathan Trujillo (November, 2010). "Two Wheel Custom Bike - Prophecy III". Lowrider Bicycle Magazine. Retrieved 2013-01-24. "laced up a pair of 144-spoke Phoenix wheels"
- Rene Vargas (March, 2009). "Custom Tricycle - Dragon's Defeat". Lowrider Bicycle Magazine. Retrieved 2013-01-24. "a set of 144-spoke wheels wrapped with 20x1.75 white walls. Of the 144 spokes, Freddie chose to have 72 of them twisted"
- Sheldon Brown. "Lacing". Retrieved 2013-01-24.
- Sheldon Brown. "Spoke patterns". Retrieved 2013-01-24.
- "Sheldon Brown Glossary: Dish". Archived from the original on 22 June 2008. Retrieved 2008-06-09.
- "Sheldon Brown Wheel Building: Spoke Torsion". Archived from the original on 15 May 2008. Retrieved 2008-05-28.
- "ACS Mag Wheels". Retrieved 209-01-26.
- Josh Patterson (Oct 9, 2012). "650b mountain bike wheels: looking at the trends". BikeRadar.com. Retrieved 2013-04-19.
- Michael Frank (April 16, 2013). "The New Mountain Bike Revolution: 27.5-Inch Wheels". Adventure Journal. Retrieved 2013-05-12.
- Lennard Zinn (April 24, 2013). "Back to 27.5". VeloNews. Retrieved 2013-05-12.
- Matt Phillips (2013). "Reviewed: 27.5 Mountain Bikes for All Trails". Mountain Bike. Retrieved 2013-05-12.
- Vernon Felton (2013). "Ready or Not, Here Comes 650". Bike Magazine. Retrieved 2013-05-12.
- Sheldon Brown (December 6, 2012). "Tire Sizing Systems". Retrieved 2013-04-10.
- "The 650B Wheel Renaissance". RideYourBike.com. Retrieved 2013-04-10.
- Guide to 650b wheels, Bikeradar.com.
- "Tire Sizing by Sheldon "ISO/E.T.R.T.O." Brown". Archived from the original on 8 January 2008. Retrieved 2008-01-01.
- "Metric bicycle tire and rim designations". cl.cam.ac.uk. Archived from the original on 22 September 2010. Retrieved September 24, 2010.
- Sheldon Brown. "Fractional sizes". Retrieved 2012-06-07.
- www.rideyourbike.com The 650B Wheel Renaissance - Retrieved 2013-04-10
- www.sheldonbrown.com/tire-sizing, Traditional Sizing Systems, Retrieved 9 september 2012.
- Sheldon Brown. "650B (584 mm) Conversions for Road Bikes". Retrieved 2011-12-23.
- "VREDESTEIN Bicycle Tires". Retrieved 2006-08-14.
- Whitt, Frank R.; David G. Wilson (1982). Bicycling Science (Second ed.). Massachusetts Institute of Technology. p. 119. ISBN 0-262-23111-5.
- Forester, John (August 1980). "Held Up By Downward Pull". American Wheelmen.
- Whitt, Frank R.; David G. Wilson (1982). Bicycling Science (Second ed.). Massachusetts Institute of Technology. pp. 106–138. ISBN 0-262-23111-5.
- Ian Smith. "Bicycle Wheel Analysis". Retrieved 2008-12-31. "I conclude that it is perfectly reasonable to say that the hub stands on the lower spokes, and that it does not hang from the upper spokes."
- C.J. Burgoyne and R. Dilmaghanian (March 1993). "Bicycle Wheel as Prestressed Structure" (pdf). Journal of Engineering Mechanics 119 (3): 439–455. ISSN 0733-9399/93/0003-0439. "Only the spokes in contact with the ground, or near the ground, show significant strains."
- Brandt, Jobst (1981). The Bicycle Wheel. Avocet. pp. 12–20. ISBN 0-9607236-2-5.
- Wilson, David Gordon; Jim Papadopoulos (2004). Bicycling Science (Third ed.). Massachusetts Institute of Technology. pp. 389–390. ISBN 0-262-73154-1.
- Tom Fine (September 1998). "Hubs hang from the rim!". Retrieved 2010-03-16. "I still say, without any doubt, that the hub hangs from the upper spokes."
- Henri P. Gavin (August 1996). "Bicycle Wheel Spoke Patterns and Spoke Fatigue" (pdf). ASCE Journal of Engineering Mechanics 122 (8): 736–742. doi:10.1061/(ASCE)0733-9399(1996)122:8(736).
- Kraig Willett (5 September 2004). "Hang or Stand?". BikeTech Review. Retrieved 2010-03-16. "A little known semantic debate ... has been raging on the usenet newsgroups for quite some time. The point of contention in this debate is whether or not a loaded bicycle wheel "stands" on the bottom spokes or "hangs" from the top ones?"
- John Swanson (2006). "Performance of the Bicycle Wheel, A Method for Analysis". BikePhysics.com. Retrieved 2012-06-25. "Radial Stiffness: There's almost -no- vertical compliance in your wheel and people who insist that they can feel the vertical stiffness or “harshness” of a wheel are mistaken. The radial stiffness of a bicycle wheel is ~ 3-4000 N/mm. This equals a deflection of 0.1 mm under a 40 kg load. Sorry princess, but that gets obscured by the amount of deflection in the tires, fork, saddle, handlebar tape, frame, and even your gloves."
- Henri P. Gavin (1996). "Bicycle Wheel Spoke Patterns and Spoke Fatigue". ASCE Journal of Engineering Mechanics. Retrieved 2012-06-25. "radial wheel stiffness (N/mm): 2500-5000"
- Ian (2002). "Spoke Patterns". astounding.org.uk. Retrieved 2012-06-25. "A radially spoked wheel is about 4.6% stiffer than a tangentially spoked one. Alternatively, if you apply 1000N (about 100kg, 220lb) to each of the wheels, the tangential (four-cross) spoked one deflects 0.0075mm (0.0003 inch) more than the radial spoked. Since the tyre is likely to deflect several millimetres at least (if 3mm, that's 400 times more deflection) I conclude the spoking is unlikely to make a discernible difference to the vertical stiffness of the wheel."
- Jobst Brandt (1981). "Sheldon Brown's Bicycle Glossary: Radial spoking". Sheldon Brown (bicycle mechanic). Retrieved 2012-06-25. "There is no change in radial elasticity between a radial and crossed spoke wheel with the same components, other than the length of the spokes. A 290 mm spoke is 3% stiffer than a 300 mm spoke of the same type. Since spokes stretch elastically about 0.1mm on a hard bump (not ordinary road ripples), the elastic difference between the radial and cross-three wheel is 3% x 0.1mm = 0.003 mm. Copier paper is 0.075 mm thick, and if you can feel that when you ride over it on a glassy smooth concrete surface, please let me know. You have greater sensitivity than the lady in "the princess and the pea" fable."
- Sheldon Brown. "Sheldon Brown's Glossary: Dish". Archived from the original on 4 December 2008. Retrieved 2008-11-30.
- Sheldon Brown. "Wheelbuilding: Spokes". Retrieved 2011-03-03.
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