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A clincher bicycle tire mounted on a wheel
A cross section of a clincher tire with a puncture-preventing layer (in blue) between the casing and the tread
An inner tube rolled up for storage or to be carried as a spare

A bicycle tire is a tire that fits on the wheel of a bicycle or similar vehicle. These tires may also be used on tricycles, wheelchairs, and handcycles, frequently for racing. Bicycle tires provide an important source of suspension, generate the lateral forces necessary for balancing and turning, and generate the longitudinal forces necessary for propulsion and braking. Although the use of a pneumatic tire greatly reduces rolling resistance compared to the use of a rigid wheel or solid tire, the tires are still typically the second largest source, after wind resistance (air drag), of power consumption on a level road.[1] The modern detachable pneumatic bicycle tire contributed to the popularity and eventual dominance of the safety bicycle.[2]

Bicycle tires are also used on unicycles, tricycles, quadracycles, tandem bicycles, hand cycles, bicycle trailers, and trailer bikes.

History

[edit]
New Mail Ladies Safety bicycle, circa 1891, with solid rubber tires
A tubed, clincher tire showing the inner tube protruding between the tire and the rim
Tubular tire rolled from rim to show glue between them
Clincher cross section schematic with 1: rim, 2: rim strip, 3: rim braking surface, 4: bead core, 5: inner tube, 6: casing, 7: tread

The first bicycle "tires" were iron bands on the wooden wheels of velocipedes.[3] These were followed by solid rubber tires on penny-farthings.[4] The first patent for "rubberized wheels" was granted to Clément Ader in 1868.[5] In an attempt to soften the ride, rubber tires with a hollow core were also tried.[6]

The first practical pneumatic tire was made by John Boyd Dunlop in 1887 for his son's bicycle, in an effort to prevent the headaches his son had while riding on rough roads. (Dunlop's patent was later declared invalid because of prior art by fellow Scot Robert William Thomson.) Dunlop is credited with "realizing rubber could withstand the wear and tear of being a tire while retaining its resilience".[7] This led to the founding of Dunlop Pneumatic Tyre Co. Ltd in 1889. By 1890, it began adding a tough canvas layer to the rubber to reduce punctures. Racers quickly adopted the pneumatic tire for the increase in speed and ride quality it enabled.

Finally, the detachable tire was introduced in 1891 by Édouard Michelin. It was held on the rim with clamps, instead of glue, and could be removed to replace or patch the separate inner tube.[2]

Attaching to the rim

[edit]

Three main techniques for attaching a bicycle tire to a bicycle rim have been developed: clincher, wired and tubular.[8] Clinchers originally did not have wire in the beads and the shape of the bead interlocked with a flange on the rim, relying on air pressure to hold the tire bead in place. However, this type of tire is no longer in general use and the term clincher has transferred to the modern wired-on tire. For the remainder of this article, the modern use of the word clincher will be assumed.

In an attempt to provide the best attributes of both wired and tubular methods, tubular clinchers have also been offered.[9]

Clincher

[edit]

Most bicycle tires are clincher types for use with "clincher" rims. These tires have a steel wire or Kevlar fiber bead that interlocks with flanges inside of the rim. A separate airtight inner tube enclosed by the tire supports the tire carcass and maintains the bead lock. An advantage of this system is that the inner tube can be easily accessed for a patch repair or replacement of the tube.

The ISO 5775-2 standard defines designations for bicycle rims. It distinguishes between

  1. Straight-side (SS) rims
  2. Crochet-type (C) rims
  3. Hooked-bead (HB) rims

Traditional wired-on rims were straight-sided. Various "hook" (also called "crochet") designs re-emerged in the 1970s to seat the tire bead on the wheel rim and hold the tire in place,[10][11] resulting in the modern clincher design. This allows higher (80–150 psi or 6–10 bar) air pressures than was possible older wired-on tires. In these designs, it is the interlocking of the bead with the rim flanges, not the tight fit or resistance to stretching of the bead, that keeps the tire on the rim and retains the air pressure.[12]

Some clincher tires can be used without tubes in a system which is referred to as tubeless. Typical tubeless tires have airtight sidewalls and beads which are designed to maximize the seal between the tyre and the wheel rim.

Tubular or sew-up

[edit]
Main article: Tubular tyre

Some tires are torus-shaped and attached to tubular rims with adhesive. Tubular rims are designed with shallow circular cross-section beds in which the tires seat instead of being attached to rim flanges by tire beads as in clincher types.

Providing suspension

[edit]

Adequate tire casing stiffness is necessary to support the rider, while softness and flexibility in the casing is desirable for cushioning. Most bicycle tires are pneumatic, the stiffness of the tires is easily controlled by controlling the air pressure inside of the tire. Airless tires utilize a semi solid sponge type elastomer material which eliminates air loss through punctures and air seepage.

Pneumatic tires

[edit]
A bicycle inner tube with valve stem undergoing a leak test in water

In a pneumatic tire, pressurized air is held inside either with a separate, relatively impermeable inner tube, or by the tire and rim, in a tubeless system. Pneumatic tires are superior in providing effective cushioning while keeping rolling resistance very low.

Tubed

[edit]

A tubed tire has a separate inner tube, made of butyl rubber, latex, or TPU (thermoplastic polyurethane) that provides a relatively airtight barrier inside the tire.[13] A vast majority of the tire systems in use are clinchers, due to the relative simplicity of repairs and wide availability of replacement inner tubes.

Most of bicycle inner tubes are torus-shaped balloons while some are not. For example, inner tubes in bicycles of the Moscow bike-sharing service are simply rubber tubes long enough to be coiled and inserted into a tire.[14]

Tubeless

[edit]
Further information: Tubeless tire

Tubeless tires are primarily used on mountain bikes due to their ability to use low air pressure for better traction without getting pinch flats.[15] Tubeless tires work similarly to clinchers in that the bead of the tire is specifically designed to interlock into a corresponding tubeless rim, but without an inner tube. Air is inflated directly into the tire, and once "locked" into the rim, the system is airtight. Liquid sealants are often injected into tubeless tires to improve sealing and to stop leaks caused by punctures. An advantage is that pinch flats are less common in a tubeless setup because they require a hole through the tire carcass, not just the inner tube. A disadvantage is that air can escape if the bead lock is compromised from too much lateral force on the tire or deformation of the rim/tire due to hard impact with an object.

Tubeless tires require tubeless-compatible rims, which do not allow air to escape where the spokes connect and have a different shape groove for the tire bead to seat.

Road tubeless
[edit]

In 2006, Shimano and Hutchinson introduced a tubeless system for road bicycles.[16] Tubeless tires have not yet gained popular acceptance in road racing due to lack of sponsorship, the tradition of using tubular tires and the fact that, even without the inner tube, the combined weight of tubeless rims and tires is more than top-of-the-line tubular tire wheelsets.[17] Road tubeless is gaining popularity among riders for whom the benefits are worth the costs.[18] Road tubeless tires tend to be a much tighter fit than traditional clincher tires, which makes mounting and removing the tire more difficult.

Airless tires

[edit]
Mobike airless tire

Airless were used before pneumatic tires were developed, appearing on velocipedes by 1869.[19][20] They continue to be developed in an effort to solve the problem of losing air pressure, either from a puncture or from permeability. Modern examples of airless tires for bicycles include BriTek's Energy Return Wheel,[21] an airless bicycle tire from Bridgestone,[22] the tire pictured to the right on a Mobike, and solid tires discussed below. Although modern airless tires are better than early ones, most give a rough ride and may damage the wheel or bicycle.[23]

Solid

[edit]

The most common form of airless tire is simply the solid tire. Besides solid rubber, solid tires made of polyurethane[24][25][26][27][28] or microcellular foam[29] are also offered for 100% flat prevention. Much of the desirable suspension quality of the pneumatic tire is lost, however, and ride quality suffers.[30]

Many bicycle-sharing systems use these tires to reduce maintenance, and examples of solid tires include those available from Greentyre,[31] Puncture Proof Tyres Ltd,[32] KIK-Reifen,[33] Tannus,[31] Hutchinson,[34] and Specialized.[35]

Construction

[edit]

Bicycle tires consist of a rubber-impregnated cloth casing, also called the carcass, with additional rubber, called the tread, on the surface that contacts the road. In the case of clinchers, the casing wraps around two beads, one on each edge.

Casing

[edit]

Bicycle tire casing is made of cloth, usually nylon, though cotton and silk have also been used. The casing provides the resistance against stretching necessary to contain the internal air pressure while remaining flexible enough to conform to the ground surface. The thread count of the cloth affects the weight and performance of the tire, and high thread counts improve ride quality and reduce rolling resistance at the expense of durability and puncture resistance.

Bias ply

[edit]

The fibers of the cloth in most bicycle tires are not woven together, but kept in separate plies so that they can move more freely to reduce wear and rolling resistance. They are also usually oriented diagonally, forming bias plies.[36]

Radial ply

[edit]

Radial ply has been attempted, and examples include Panasonic in the 1980s and the Maxxis in the 2010s,[36] but often found to provide undesirable handling characteristics.[37]

Tread

[edit]
Different treads on knobby mountain bike tires
A slick tire with squared-off tread profile
Two tires of the same make and tread pattern, the lower one completely unused, the upper one has rolled over 1500 kilometers on varying surfaces.

The tread is the part of the tire that contacts the ground to provide grip and protect the casing from wear.

Compound

The tread is made of natural and synthetic rubber that often includes fillers such as carbon black, which gives it its characteristic color, and silica.[38] The type and amount of filler is selected based on characteristics such as wear, traction (wet and dry), rolling resistance, and cost. Oils and lubricants may be added as softeners.[38] Sulphur and zinc oxide facilitate vulcanization.[38] Some tires have a dual-compound tread that is tougher in the middle and grippier on the edges.[39] Many modern tires are available with treads in a variety or combination of colors.[40][41] Road racing tires with different tread compounds for the front and rear have been developed, thereby attempting to provide more traction in front and less rolling resistance in the rear.[42]

Pattern

Treads fall somewhere along the spectrum from smooth or slick to knobby. Smooth treads are intended for on-road use, where a tread pattern offers little to no improvement in traction.[43] However, many otherwise slick tires have a light tread pattern, due to the common misbelief that a slick tire will be slippery in wet conditions. Knobby treads are intended for off-road use, where the tread texture can help improve traction on soft surfaces. Many treads are omnidirectional—the tire can be installed in either orientation—but some are unidirectional and designed to be oriented in a specific direction. Some tires, especially for mountain bikes, have a tread which is intended either for the front wheel or the rear wheel.[44] A special tread pattern, with small dimples, has been developed to reduce air drag.[45]

Profile

The profile of the tread is usually circular, matching the shape of the casing inside it and allowing the tire to roll to the side as the bicycle leans for turning or balancing. More-squared profiles are sometimes used on mountain bike tires and novelty tires designed to look like automotive racing slicks,[46] as on wheelie bikes.

Bead

[edit]

The bead of clincher tires must be made of a material that will stretch very little to prevent the tire from expanding off of the rim under internal air pressure.

Wire

Steel wire beads are used on inexpensive tires. Though they cannot be folded, they can often be twisted into three smaller hoops.[47]

Kevlar
A foldable mountain and road bicycle tire

Kevlar beads are used on expensive tires, and these are also called "foldable". They should not be used on straight sidewall rims as they may blow off the rim.

Sidewall

[edit]
Further information: Sidewall

The sidewall of the casing, the part not intended to contact the ground, may receive one of several treatments.

Gum wall

Tires with sidewalls made of natural rubber are called "gum wall". The tan colored, natural rubber lacks carbon black to decrease rolling resistance, as its added wear resistance isn't needed in the sidewall.[48]

Skin wall

Tires with very little rubber, if any, covering the sidewall are called "skin wall". This reduces rolling resistance by reducing sidewall stiffness at the cost of reducing damage protection.[49]

Variations

[edit]
A punctured tire.

Puncture resistance

[edit]

Some tires include an extra layer between the tread and the casing (as shown in the cross section pictured above) to help prevent punctures either by being tough or simply by being thick. These extra layers are usually associated with higher rolling resistance.[50]

Studs

[edit]
A studded, knobby tire

Metal studs may be embedded in the tread of knobby tires to improve traction on ice.[51] Inexpensive studded tires use steel studs, while pricier tires use more durable carbide studs.[52] A studded, knobby tread that zips onto a smoother, non-studded tire has been developed to ease the transition between the two types of tires.[53][54][55]

Reflective

[edit]

Some tires have a reflective strip on their sidewalls to improve visibility at night. Others have reflective material embedded in the tread.[41]

Aerodynamics

[edit]

In addition to the dimple tread pattern mentioned above, at least one tire has an extra "wing" to cover the gap between the tire sidewall and the wheel rim and reduce drag.[56]

Indoor use

[edit]

At least one modern bicycle tire has been designed specifically for indoor use on rollers or trainers. It minimizes excessive wear that traditional tires experience in this environment and is not suitable for use on pavement.[57]

Different front and rear

[edit]

Besides the different tread patterns available on some mountain bike tires mentioned above, front and rear tire sets are available for road bikes with different tread patterns, tread compounds, and sizes for the front and rear wheels.[58] Other scenarios involve replacing a damaged tire, and leaving the other one unchanged.

Self inflating

[edit]

Bicycle tires have been developed that pump themselves up as they roll forward.[59][60]

Modular

[edit]

Bicycle tires have been developed so that different treads can be zipped on and off. This allows having the additional traction of studded tires only when necessary and avoiding the additional rolling resistance otherwise.[61][62][63][64]

Parameters

[edit]

Sizes

[edit]
Tire-size designations on the side of a tire

The modern tire-size designations (e.g. "37-622", also known as ETRTO) are defined by international standard ISO 5775, along with corresponding rim size designations (e.g., "622×19C"). Older English (inch, e.g. "28 × 1+5⁄8 × 1+3⁄8") and French (metric, e.g. "700×35C") designations are also still used, but can be ambiguous. The diameter of the tire must match the diameter of the rim, but the width of the tire only has to be in the range of widths appropriate for the width of the rim,[65] while also not exceeding the clearances allowed by the frame, brakes, and any accessories such as fenders. Diameters vary from a large 910 mm, for touring unicycles, to a small 125 mm, for roller skiing.[66] Widths vary from a narrow 18 mm to a wide 119 mm for the Surly Big Fat Larry.[67]

Further information: Bicycle wheel § Sizes

Lightweight tires

[edit]

Lightweight tires range in size from 3⁄4 to 1+1⁄8 inches (19 to 29 mm) wide.

Middleweight or Demi-balloon tires

[edit]

Middleweight or Demi-balloon tires range in size from 1+1⁄8 to 1+3⁄4 inches (29 to 44 mm) wide.

Balloon tires

[edit]

A balloon tire is a type of wide, large-volume, low-pressure tire that first appeared on cruiser bicycles in the US in the 1930s. They are typically 2 to 2.5 inches (51 to 64 mm) wide.

In the 1960s Raleigh made its small-wheeled RSW 16 with balloon tires[68] so it would have a soft ride like the fully suspended Moulton Bicycle. Other manufacturers then used the same idea for their own small wheelers. Examples include the Stanningley (UK)-made Bootie Folding Bicycle, the Co-operative Wholesale Society (CWS) Commuter, and the Trusty Spacemaster.

62-203 Michelin balloon tire on front wheel of 1960s Bootie Folding Cycle

Plus-size tires

[edit]

A plus-size tire has a width of typically 2.5–3.25 inches (64–83 mm). Three bead seat diameters are available: 559 mm for 26+, 584 mm for 27.5+ (650B+), and 622 mm for 29+. They fill the gap between balloon and fat tires.[69]

Fat tires

[edit]

A fat tire is a type of wide oversized bicycle tire, typically 3.8 in (97 mm) or larger and rims 2.6 in (66 mm) or wider, designed for low ground pressure to allow riding on soft unstable terrain, such as snow, sand, bogs, and mud.[70] Since the 1980s, fat tires of width 3.8 to 5 in (97 to 127 mm), and diameters similar to conventional bicycle wheels, have been used on "fatbikes" and all-terrain bikes designed for riding in snow and sand.[71][72]

Inflation pressure

[edit]

The inflation pressure of bicycle tires ranges from 4.5 psi (0.31 bar; 31 kPa) for fat bike tires in snow[73] to 220 psi (15 bar; 1.5 MPa) for tubular track racing tires.[74] The maximum pressure rating of tires is usually stamped on the sidewall, indicated as "Maximum Pressure", or "Inflate to ..." or sometimes expressed as a range like "5–7 bar (73–102 psi; 500–700 kPa)". Decreasing pressure tends to increase traction and make the ride more comfortable while increasing pressure tends to make the ride more efficient and decreases the chances of getting pinch flats.[75]

One published guideline for clincher inflation pressure is to pick the value for each wheel that produces a 15% reduction in the distance between the wheel rim and the ground when loaded (i.e. with the rider and cargo) compared to when unloaded. Pressures below this leads to increased rolling resistance and likelihood of pinch-flats. Pressures above this leads to less rolling resistance in the tire itself but to larger total energy dissipation caused by passing vibrations to the bike and especially the rider, which experience elastic hysterisis.[76][77] Inner tubes are not completely impermeable to air and slowly lose pressure over time. Butyl inner tubes hold pressure better than latex.[78] Tires inflated from carbon dioxide canisters (often used for roadside repairs) or helium (occasionally used for elite track racing) lose pressure more quickly, because carbon dioxide, despite being a relatively large molecule, is slightly soluble in rubber,[79] and helium is a very small atom which passes quickly through any porous material. At least one public bicycle sharing system, London's Santander Cycles, is inflating tires with nitrogen, instead of simple air, which is already 78% nitrogen, in an attempt to keep the tires at the proper inflation pressure longer,[80] though the effectiveness of this is debatable.[81][82][83]

Effect of temperature

[edit]

Since the volume of gas and the gas itself inside a tire is not altered significantly by a change of temperature, the ideal gas law states that the pressure of the gas should be directly proportional to the absolute temperature. Thus, if a tire is inflated to a gauge pressure of 4.00 bar (400 kPa; 58.0 psi) at room temperature, 20 °C (68 °F), the gauge pressure will increase to 4.34 bar (434 kPa; 62.9 psi) (+8.5%) at 40 °C (104 °F) and decrease to 3.66 bar (366 kPa; 53.1 psi) (-8.5%) at 0 °C (32 °F).

In the example above, a 7.0% difference in absolute temperature resulted in a 8.5% difference in tire pressure. This is a result of the difference between gauge pressure and absolute pressure. For low inflation pressures, this distinction is more important, as the ideal gas law applies to absolute pressure, including atmospheric pressure. For example, if a fat-bike tire is inflated to 0.50 bar (50 kPa; 7.3 psi) gauge pressure at room temperature 20 °C (68 °F) and then the temperature is decreased to −10 °C (14 °F) (a 10% decrease in absolute temperature), the absolute pressure of 1.50 bar (150 kPa; 21.8 psi) will be decreased by 10% to 1.35 bar (135 kPa; 19.6 psi), which translates to a 30% decrease in gauge pressure, to 0.35 bar (35 kPa; 5.1 psi).

Effect of atmospheric pressure

[edit]

The net air pressure on the tire is the difference between the internal inflation pressure and the external atmospheric pressure, 1 bar (100 kPa; 15 psi), and most tire pressure gauges report this difference. If a tire is inflated to 4 bar (400 kPa; 58 psi) at sea level, the absolute internal pressure would be 5 bar (500 kPa; 73 psi) (+25%), and this is the pressure that the tire would need to contain if it were moved to a location with no atmospheric pressure, such as the vacuum of free space. At the highest elevation of commercial air travel, 12,000 metres (39,000 ft), the atmospheric pressure is reduced to 0.2 bar (20 kPa; 2.9 psi), and that same tire would have to contain 4.8 bar (480 kPa; 70 psi) (+20%).

Effect on carcass stress

[edit]

Bicycle tires are essentially toroidal thin-walled pressure vessels and if the carcass is treated as a homogeneous and isotropic material then stress in the toroidal direction (longitudinal or axial stress if the tire is considered a long cylinder) can be calculated as:[84][85]

,

where:

  • p is internal gauge pressure
  • r is the inner, minor radius of the carcass
  • t is thickness of the carcass

Stress in the poloidal direction (hoop or circumferential stress if the tire is considered a long cylinder) is more complicated, varying around the minor circumference and depending on the ratio between the major and minor radii, but if the major radius is much larger than the minor radius, as on most bicycle tires where the major radius is measure in hundreds of mm and the minor radius is measured in tens of mm, then stress in the Poloidal direction is close to the hoop stress of cylindrical thin-walled pressure vessels:[84][85]

.

In reality, of course, the tire carcass is not homogeneous nor isotropic, but instead is a composite material with fibers imbedded in a rubber matrix, which complicates things further.

Rim width

[edit]

While not strictly a tire parameter, the width of the rim on which any given tire is mounted has an influence on the size and shape of the contact patch, and possibly the rolling resistance and handling characteristics.[86] The European Tyre and Rim Technical Organisation (ETRTO) publishes a guideline of recommended rim widths for different tire widths:[87]

ETRTO approved rim width (mm) (2003 ed.)
tire width straight rim width crotchet rim width
18 - 13C
20 - 13C
23 16 13C-15C
25 16-18 13C-17C
28 16-20 15C-19C
32 16-20 15C-19C
35 18-22 17C-21C
37 18-22 17C-21C
40 20-24 19C-23C
44 20-27 19C-25C
47 20-27 19C-25C
50 22–30.5 21C-25C
54 27–30.5 25C-29C
57 27–30.5 25C-29C
62 30.5 29C

In 2006, it was expanded for allowing wide tires up to 50mm on 17C rims and 62mm on 19C rims.[88] Ideally, the tire width should be 1.8 to 2 times the rim width, but a ratio from 1.4 to 2.2 should fit, and even 3 for hooked rims.[89]

Tire pressure versus width

[edit]

Mavic recommends maximum pressures in addition to rim width,[90] and Schwalbe recommends specific pressures:[91]

Schwalbe and Mavic pressure recommendations
tire width Schwalbe rec. Mavic max. rim
18 mm (0.71 in) 10.0 bars (145 psi) 13C
20 mm (0.79 in) 9.0 bars (131 psi) 9.5 bars (138 psi) 13C
23 mm (0.91 in) 8.0 bars (116 psi) 9.5 bars (138 psi) 13C-15C
25 mm (0.98 in) 7.0 bars (102 psi) 9.0 bars (131 psi) 13C-17C
28 mm (1.1 in) 6.0 bars (87 psi) 8.0 bars (116 psi) 15C-19C
32 mm (1.3 in) 5.0 bars (73 psi) 6.7 bars (97 psi) 15C-19C
35 mm (1.4 in) 4.5 bars (65 psi) 6.3 bars (91 psi) 17C-21C
37 mm (1.5 in) 4.5 bars (65 psi) 6.0 bars (87 psi) 17C-23C
40 mm (1.6 in) 4.0 bars (58 psi) 5.7 bars (83 psi) 17C-23C
44 mm (1.7 in) 3.5 bars (51 psi) 5.2 bars (75 psi) 17C-25C
47 mm (1.9 in) 3.5 bars (51 psi) 4.8 bars (70 psi) 17C-27C
50 mm (2.0 in) 3.0 bars (44 psi) 4.5 bars (65 psi) 17C-27C
54 mm (2.1 in) 2.5 bars (36 psi) 4.0 bars (58 psi) 19C-29C
56 mm (2.2 in) 2.2 bars (32 psi) 3.7 bars (54 psi) 19C-29C
60 mm (2.4 in) 2.0 bars (29 psi) 3.4 bars (49 psi) 19C-29C
63 mm (2.5 in) 3.0 bars (44 psi) 21C-29C
66 mm (2.6 in) 2.8 bars (41 psi) 21C-29C
71 mm (2.8 in) 2.5 bars (36 psi) 23C-29C
76 mm (3.0 in) 2.1 bars (30 psi) 23C-29C

Fatbike tires of 100 to 130 mm (4 to 5 inches) width are typically mounted on 65 to 100 mm rims.[92]

Forces and moments generated

[edit]

Bicycle tires generate forces and moments between the wheel rim and the pavement that can affect bicycle performance, stability, and handling.

Vertical force

[edit]

The vertical force generated by a bicycle tire is approximately equal to the product of inflation pressure and contact patch area.[93] In reality, it is usually slightly more than this because of the small but finite rigidity of the sidewalls.

The vertical stiffness, or spring rate, of a bicycle tire, as with motorcycle and automobile tires, increases with inflation pressure.[94]

Rolling resistance

[edit]

Rolling resistance is a complex function of vertical load, inflation pressure, tire width, wheel diameter, the materials and methods used to construct the tire, roughness of the surface on which it rolls, and the speed at which it rolls.[1] Rolling resistance coefficients may vary from 0.002 to 0.010,[1][74][95][96] and have been found to increase with vertical load, surface roughness, and speed.[1][97] Conversely, increased inflation pressure (up to a limit), wider tires (compared to narrower tires at the same pressure and of the same material and construction),[98] larger-diameter wheels,[99] thinner casing layers, and more-elastic tread material all tend to decrease rolling resistance.

For example, a study at the University of Oldenburg found that Schwalbe Standard GW HS 159 tires, all with a width of 47 mm and an inflation pressure of 300 kPa (3.0 bar; 44 psi), but made for various diameter rims, had the following rolling resistances:[100]

ISO Size Tire diameter (mm) Crr
47-305 351 0.00614
47-406 452 0.00455
47-507 553 0.00408
47-559 605 0.00332
47-622 668 0.00336

The author of the cited paper concludes, based on the data presented therein, that Crr is inversely proportional to inflation pressure and to wheel diameter.

Although increasing inflation pressure tends to decrease rolling resistance because it reduces tire deformation, on rough surfaces increasing inflation pressure tends to increase the vibration experienced by the bicycle and rider, where that energy is dissipated in their less-than-perfectly-inelastic deformation. Thus, depending on the myriad of factors involved, increasing inflation pressure can lead to increasing total energy dissipation and either slower speed or higher energy consumption.[101]

Cornering force and camber thrust

[edit]

As with other pneumatic tires, bicycle tires generate cornering force that varies with slip angle and camber thrust that varies with camber angle. These forces have been measured by several researchers since the 1970s,[102][103] and have been shown to influence bicycle stability.[104][105]

Moments

[edit]

Moments generated in the contact patch by a pneumatic tire include the self aligning torque associated with cornering force, twisting torque associated with camber thrust, both about a vertical axis, and an overturning moment about the roll axis of the bike.[106]

See also

[edit]

References

[edit]
[edit]
Revisions and contributorsEdit on WikipediaRead on Wikipedia

Bicycle tire

View on Grokipedia
from Grokipedia
A bicycle tire is the inflatable or solid outer component of a bicycle wheel that provides traction, shock absorption, and load support by interfacing directly with the ground. It typically consists of a rubber tread for grip, a fabric-reinforced casing for structure, and beads that secure it to the rim, enabling efficient power transfer and durability across various terrains. Bicycle tires are constructed from specialized materials to balance performance attributes like rolling resistance, puncture resistance, and wet-weather grip. The tread is primarily made of natural and synthetic rubber compounds, blended with fillers such as carbon black and silica to enhance traction and longevity; emerging designs as of 2025 incorporate sustainable options like recycled or bio-based materials. The casing, or carcass, uses nylon (polyamide) fabric for stability and flexibility, while sidewalls are rubber-coated nylon for lateral support. Beads incorporate steel wire or aramid fibers (like Kevlar) to lock onto the rim, and protective layers such as Kevlar belts add puncture resistance. Tires are categorized by construction type and intended use, influencing their design and performance. Clincher tires, the most common type, feature a separate inner tube and are easily installed on hooked rims for everyday riding. Tubular tires have the inner tube sewn directly into the casing and are glued to the rim, offering lower rolling resistance for racing. Tubeless tires eliminate the inner tube, using sealant to maintain air pressure and allowing lower operating pressures for improved comfort and grip on rough surfaces. By use, road tires prioritize speed with smooth treads and high pressures, while mountain bike tires emphasize durability with knobby patterns and lower pressures suited to off-road conditions. Detailed types, pressures, and standards are covered in subsequent sections.

Fundamentals

Definition and Function

A bicycle tire is the outer covering, typically made of rubber or synthetic materials, that encircles the wheel rim and forms the primary point of contact with the ground. It interfaces with the rim to secure the wheel assembly and, in many designs, works in conjunction with an inner tube to maintain air pressure within the tire structure. The tire performs several essential functions critical to bicycle operation. It provides load-bearing support by distributing the weight of the rider and bicycle across the contact patch with the ground, enabling stable handling. Traction is achieved through the tire's surface grip, facilitating effective acceleration, braking, and cornering on various terrains. Additionally, it dampens vibrations from road irregularities, enhancing rider comfort and control, while optimizing energy transfer to minimize pedaling resistance and improve efficiency. Bicycle tires have evolved from early solid rubber forms, which offered limited cushioning, to modern pneumatic designs that utilize air pressure for superior shock absorption and ride quality. While pneumatic tires dominate due to their balanced performance, airless alternatives have emerged for puncture-resistant applications.

Basic Components

A standard bicycle tire consists of several key components that work together to provide support, traction, and durability. The primary parts include the casing, tread, sidewall, bead, and optionally an inner tube. These elements form a flexible, airtight structure that maintains contact with the road while absorbing shocks and transmitting forces from the rider. The casing serves as the foundational body of the tire, composed of multiple layers of cord fabric plies that provide structural integrity and flexibility. These plies are typically made from materials such as nylon, cotton, or polyester, woven tightly and measured by threads per inch (TPI), where higher TPI values like 120 contribute to a lighter and more supple ride compared to lower values like 60. The casing encases the air pressure and supports the overall tire shape under load. The tread forms the outermost surface that contacts the ground, designed primarily for grip and wear resistance. It is constructed from rubber compounds, either natural rubber for better elasticity and lower rolling resistance or synthetic variants like styrene-butadiene rubber (SBR) for enhanced durability, often blended together. These compounds are often reinforced with additives such as carbon black or silica to balance traction and longevity, with softer formulations providing superior grip on varied surfaces while harder ones prioritize speed and endurance. The sidewall connects the tread to the bead, offering flexible flanks that protect the casing from impacts and allow the tire to conform to terrain irregularities. Made from the same cord fabric as the casing but thinner, the sidewall includes printed information on tire specifications and directional indicators for proper installation. It is typically coated with a weather-resistant rubber layer to prevent cracking from environmental exposure. The bead anchors the tire to the rim, consisting of a bundle of high-strength wire or fiber—such as steel wire for cost-effective options or aramid (e.g., Kevlar) for lightweight performance tires—that forms a rigid edge. This component ensures the tire remains securely seated during inflation and use. In many designs, an optional inner tube made of butyl rubber provides the airtight seal to retain air pressure, though tubeless systems eliminate this by using sealant and an airtight casing liner. The components integrate cohesively: the casing wraps around the bead to create a U-shaped profile, with the tread and sidewall layers bonded via vulcanization to the cord fabric, forming a unified structure that distributes stress evenly and maintains inflation integrity. Common failure points include sidewall tears from curb impacts or sharp debris, which can expose the casing and lead to air loss, and bead unseating due to insufficient inflation or excessive lateral forces, causing the tire to slip off the rim. Prevention involves maintaining recommended tire pressure (typically 30-120 psi depending on tire size and use), regularly inspecting for cuts or embedded objects, and selecting tires with reinforced sidewalls or puncture-resistant layers for high-risk conditions.

Historical Development

Early Inventions

In the mid-19th century, early bicycles known as velocipedes featured solid rubber tires, marking a significant improvement over previous iron-banded wooden wheels. French blacksmith Pierre Michaux introduced these solid rubber tires to his pedal-driven velocipedes around 1868, fitting them to the iron rims to provide greater durability and some cushioning against road imperfections. Despite this advancement, the tires offered a notoriously harsh ride, earning the velocipede the nickname "boneshaker" due to the unyielding contact with cobblestone and dirt paths, which transmitted vibrations directly to the rider. The pneumatic tire revolutionized bicycle comfort when Scottish veterinarian John Boyd Dunlop patented the first practical air-filled design in 1888, initially for his son's tricycle to alleviate the jarring effects of solid tires on rough surfaces. Dunlop's invention consisted of an inflatable inner tube that absorbed shocks, significantly reducing vibration and enabling smoother, faster travel. By 1889, the technology was adapted for bicycles, with cyclist Willie Hume demonstrating its potential by winning multiple races in Ireland using Dunlop-equipped bikes, spurring rapid interest among enthusiasts and manufacturers. Early pneumatic tires were constructed using natural India rubber for the inflatable tubes, which were wrapped in canvas for reinforcement and then sewn or glued directly to the wheel rims, forming a single-unit design that was labor-intensive to produce. This canvas outer layer provided basic protection and tread, but the overall assembly relied on adhesives for attachment, limiting ease of replacement. Despite their benefits, early pneumatic tires faced substantial challenges, including frequent punctures from road debris that deflated the tubes and required on-site repairs, as well as poor adhesion where the glued canvas often detached under stress. These issues contributed to short tire lifespans, yet racers in the 1890s quickly adopted them for competitive edges in events like the precursor long-distance races to the Tour de France, such as the 1891 Paris-Brest-Paris, where the speed gains outweighed the maintenance demands.

Material and Design Evolution

In the early 20th century, bicycle tire design saw the standardization of wire beads in clincher tires, which securely hooked onto rims for reliable attachment and easier replacement compared to earlier glued designs. This innovation, developed around the 1890s and widely adopted by the 1920s, facilitated mass production and became the dominant format for wired-on tires. The mid-20th century brought key shifts in materials, driven by wartime necessities and postwar synthetic advancements. Early casings relied on cotton fabric for flexibility and strength, but transitioned to nylon plies in the 1940s and 1950s, reducing weight while maintaining durability and enabling higher performance in racing and touring applications. Post-World War II, synthetic rubbers, including butyl for inner tubes, replaced natural latex, offering superior air retention and resistance to weathering and cracking. Butyl tubes, developed in the late 1930s and commercialized during the war as a latex substitute, became standard by the 1950s, minimizing slow leaks and extending ride reliability. Further ply innovations in the 1970s introduced aramid fibers like Kevlar, initially commercialized for racing tires and adapted for bicycles in folding-bead designs by 1975, enhancing puncture resistance without the weight of steel reinforcements. This era also coincided with the mountain biking boom, prompting the development of aggressive tread patterns with knobs for off-road traction on dirt and gravel, evolving from smooth road slicks to specialized profiles that improved grip and control in rugged terrain. By the 1990s, tubeless systems emerged in the mountain bike scene, with the Universal System Tubeless (UST) standard launched in 1999 by Mavic, eliminating inner tubes to reduce rotational weight, lower rolling resistance, and enable run-flat capabilities via sealants. Recent developments through 2025 emphasize sustainability and smart integration; recycled rubber treads, such as those in Schwalbe's Green Marathon tire (80% recycled or renewable materials, including recovered carbon black from old tires), address environmental impact while maintaining performance. Self-sealing compounds, incorporating latex-based or synthetic sealants like those in Slime products, automatically mend punctures up to 6mm, building on 1980s innovations for proactive flat prevention. Additionally, smart tires now integrate sensors for real-time pressure and temperature monitoring, as seen in Zipp's 2025 wheelsets with embedded Bluetooth-enabled devices that connect to apps for optimal inflation alerts.

Construction

Casing Structure

The casing of a bicycle tire forms its foundational structural framework, consisting of multiple layers of fabric plies made from cords such as nylon or polyester, which are embedded in rubber to provide strength, flexibility, and support for the tread and sidewalls. These plies are arranged in a crisscross pattern to distribute forces evenly across the tire during riding, enabling it to withstand inflation pressures, impacts, and road deformations while maintaining shape. The choice of materials like nylon for its tensile strength or polyester for lighter weight influences the overall durability and performance of the casing. Most bicycle tires employ a bias ply construction, where the cords are laid diagonally across the tire's centerline at angles typically around 45 degrees, alternating directions between layers to create a balanced, interwoven structure. This design, common in touring and general-purpose tires, promotes even flex across the sidewall and crown, enhancing durability and puncture resistance while allowing controlled deformation under load. While most bicycle tires use bias-ply construction, some manufacturers, such as Schwalbe, have introduced radial ply constructions for certain high-performance mountain bike tires since 2024, featuring cords oriented perpendicular to the tread (approximately 90 degrees to the direction of travel) and reinforced with circumferential belts beneath the tread for added stability to reduce weight, improve handling precision, and minimize rolling resistance by decoupling sidewall and tread movements. The density of the cords in these plies is measured by threads per inch (TPI), which indicates the number of individual threads woven into the fabric per inch; lower TPI values, such as 60, use coarser threads for enhanced protection and resilience in rugged applications, while higher TPI ratings of 120 or more employ finer threads to create a lighter, more supple casing that improves ride comfort and responsiveness on smoother surfaces. Thinner casings, often found in racing-oriented designs with high TPI, allow greater compliance and vibration absorption for a smoother feel, whereas thicker casings, typical in durable models with lower TPI, provide superior impact resistance but may feel stiffer. The casing integrates with the bead area to secure the tire to the rim, ensuring airtight sealing and structural integrity under pressure.

Tread and Sidewall Design

The tread of a bicycle tire forms the outermost layer that interacts directly with the road or trail surface, providing grip, durability, and resistance to wear, while the sidewall serves as a flexible protective barrier connecting the tread to the bead. These components are engineered from specialized rubber formulations to balance performance attributes like traction, rolling efficiency, and longevity. Tread designs typically incorporate multi-layer constructions, with an outer cap optimized for surface contact and an underlying base layer promoting adhesion to the tire's internal structure. Tread composition relies on blends of natural and synthetic rubbers, typically comprising 40-60% of the mixture, combined with 15-30% fillers and 20-35% additives such as oils, vulcanizing agents, and anti-aging compounds. High-performance treads often use dual- or triple-compound layering, where a firmer base (around 65 Shore A) ensures structural integrity and adhesion, while a softer cap (55 Shore A or lower) enhances grip on the contact surface. Silica additives are commonly integrated into these compounds to improve wet traction by increasing rubber flexibility and reducing slipperiness on damp surfaces, without significantly compromising dry-road performance. Tread patterns vary to suit different riding conditions, with slick designs featuring minimal or no protrusions to minimize rolling resistance on paved roads, allowing for smoother, faster travel. Knobby patterns, characterized by tall, spaced lugs, excel in off-road environments by channeling mud and debris away from the contact patch, thereby maintaining traction in loose or wet soil. File tread patterns, with low-height, densely packed central grooves resembling a metal file, offer a compromise for mixed-use scenarios like gravel or light touring, providing moderate grip on varied surfaces while preserving reasonable efficiency. Sidewalls are constructed from thinner rubber layers to allow flex during cornering and absorb impacts without excessive stiffness, contributing to ride comfort and handling responsiveness. These areas often incorporate branding, size markings, and safety warnings embossed or printed directly into the rubber for identification and regulatory compliance. In high-end tires, dual-compound sidewall designs employ a supple outer layer paired with a more durable inner formulation to enhance flexibility while resisting cuts and abrasions. Many bicycle tires include built-in wear indicators, such as small raised bars or indentations embedded in the tread grooves, which become flush with the surface when the tread is sufficiently worn, signaling the need for replacement to maintain safe traction levels. These indicators, often positioned in four locations around the tire, help riders visually assess remaining life without specialized tools. Rubber compound hardness is measured on the Shore A durometer scale, where road-oriented tires typically range from 50-70 Shore A—firmer compounds (around 60-70 Shore A) prioritize durability and low rolling resistance, while softer ones (50-60 Shore A) improve comfort and grip on imperfect surfaces. Softer formulations, often used in the tread shoulders, enhance cornering traction but wear faster, reflecting a trade-off tailored to specific riding demands.

Bead and Reinforcement

The bead of a bicycle tire consists of a core bundle embedded in the edge of the casing to secure the tire to the rim and maintain its diameter under inflation. Typically, this core is formed from a rigid steel wire bundle that is folded into the casing, providing strength to resist slippage under torque from pedaling or braking forces. In folding tire designs, such as those used in many tubular and lightweight clincher tires, an aramid fiber (like Kevlar) bundle replaces the steel wire, allowing the tire to fold for easier transport while still ensuring a secure rim seat. Wire beads are more common in standard clincher tires for their durability and cost-effectiveness, whereas folded aramid beads reduce weight by up to 50-100 grams per tire compared to wire equivalents. Reinforcements in the bead area enhance structural integrity and protect against damage. The apex, or bead filler, is a wedge-shaped rubber layer applied above the bead core to support the sidewall, stiffen the tire's lower structure, and prevent pinch flats from rim strikes during impacts. This reinforcement is particularly vital in downhill or aggressive off-road tires, where it adds rigidity without significantly increasing overall weight. The chafer, a thin protective layer of nylon or textile fabric, wraps the bead area to shield it from abrasion against the rim, curb strikes, and environmental wear, thereby extending tire life. In tubeless systems like Universal System Tubeless (UST), the bead is designed with a thicker, square-profiled shape that interlocks precisely with compatible rims, creating an airtight seal without requiring an inner tube or sealant in certified setups. This construction minimizes stretch under pressure and ensures reliable seating, distinguishing it from standard beads by enabling lower-volume, high-performance applications. Bead seating during installation typically requires an initial inflation of 40-60 psi to snap the bead into the rim's groove, after which pressure is adjusted to the tire's recommended operating range.

Types and Attachment

Clincher Tires

Clincher tires represent the most prevalent type of bicycle tire, characterized by their wire-reinforced bead that secures the tire to the rim. In this design, the wire bead seats into the hooks of a compatible rim, where inflation pressure maintains the attachment by expanding the tire against the rim walls. These tires are compatible with inner tubes for traditional setups or can be converted to tubeless systems using sealant to seal the bead and prevent air loss. The primary advantages of clincher tires include their straightforward installation and removal, which allows quick tube replacements during rides, along with their cost-effectiveness and broad availability across manufacturers. They serve as the standard option for road, mountain bike (MTB), and hybrid bicycles due to their versatility in handling diverse terrains and pressures, typically ranging from 30-50 PSI for MTB applications to 80-120 PSI for road use. Modern clincher setups increasingly use thermoplastic polyurethane (TPU) inner tubes, which reduce rolling resistance compared to traditional butyl tubes (savings of approximately 5-10 watts per pair). However, a key disadvantage is their susceptibility to pinch flats, where impacts compress the inner tube between the tire casing and rim, causing punctures—particularly at lower pressures on rough surfaces. Clincher tires achieved dominance as the standard bicycle tire following their introduction in the 1890s, with the Bartlett Clincher patent marking a pivotal advancement in detachable pneumatic designs that replaced earlier fixed or solid options. This evolution continued into the 2010s, when hookless rims—lacking traditional bead hooks—gained popularity for simplifying tubeless setups while relying on tire bead profiles for retention, though as of 2025, they face safety controversies including blow-off risks above 72 PSI without approved tires.

Tubular Tires

Tubular tires, also known as sew-ups, feature an inner tube that is sewn directly into the tire casing along its edges, forming a unified, sausage-like structure without separate beads. This construction allows the tire to encase the tube completely, providing even pressure distribution across the entire surface. The tire is then glued directly to a compatible rim bed using a specialized adhesive, such as mastic, for a secure attachment that relies on the glue's bonding strength rather than mechanical retention. This design traces its origins to the late 19th century, with the first tubular tires developed around 1888 specifically for racing bicycles to improve speed and durability on tracks. Over time, the format evolved for elite competition, and modern iterations often incorporate latex or TPU inner tubes instead of butyl, which reduces rolling resistance by minimizing friction and hysteresis losses within the tire system. The integrated tube and casing provide uniform support that significantly lowers the incidence of pinch flats, as the tube is protected evenly from impacts against the rim. This setup also delivers a smoother ride quality due to the supple, seamless construction, and repairs are straightforward by swapping the entire pre-assembled tire rather than patching an inner tube. As a result, tubular tires remain the preferred choice for high-stakes applications, including track racing where maximum grip and speed are essential, and cyclocross events demanding quick handling on varied terrain. Despite these benefits, tubular tires present challenges in installation, requiring careful application of glue to the rim and tire base, which can be messy and time-intensive, often taking hours to cure properly. They are also more expensive to purchase and replace compared to other tire types, contributing to their rarity outside professional and dedicated enthusiast use. The even distribution of the inner tube enables tubular tires to safely operate at higher inflation pressures than many alternatives, commonly in the range of 120 to 160 psi, which supports enhanced aerodynamics and responsiveness in performance-oriented riding.

Tubeless Systems

Tubeless systems for bicycle tires eliminate the inner tube by creating an airtight seal between the tire bead and the rim, relying on a liquid sealant to maintain pressure and automatically repair small punctures. This setup uses a tubeless-compatible rim, often sealed with airtight tape over spoke holes, and a tubeless valve for inflation. The sealant, typically latex-based, coats the inner tire surface and coagulates upon contact with air from a puncture, forming a plug that seals holes up to approximately 5 mm in diameter. Common types include tubeless-ready (TLR) tires, which are essentially clincher designs with reinforced beads for secure rim seating but require sealant for airtightness, and the UST (Universal System Tubeless) standard, originally developed for mountain biking, featuring fully airtight casings that can operate without sealant though typically use it for enhanced puncture protection. TLR tires, marked on the sidewall, are lighter and more versatile for road, gravel, and cyclocross applications, while UST provides greater durability for off-road use. Other variants, such as Schwalbe's Tubeless Easy, prioritize ease of installation with specialized bead profiles. Installation involves mounting the tire onto a compatible rim, adding 60-120 ml of sealant through the valve, and using a floor pump, CO2 cartridge, or compressor to seat the bead, which may require bursts of high pressure up to 60 psi temporarily. Post-installation, riders must shake or spin the wheel and ride briefly to distribute the sealant evenly. Maintenance includes refreshing the sealant every 2-7 months or after 2,000 km, depending on conditions, by removing the valve core to inject fresh sealant and checking for drying via a test puncture. Key advantages include the ability to run lower air pressures, typically 20-40 psi for gravel and mountain bike tires, enhancing traction, comfort, and shock absorption on rough terrain without risking pinch flats common in tubed setups. Without the tube's weight (often 50-100 g per tire), systems reduce overall rotational mass for improved acceleration and efficiency, while the sealant provides immediate puncture sealing to minimize downtime. Rolling resistance is also lowered due to the absence of tube-tire friction, with tests showing gains of 3-6 watts on gravel tires. Tubeless technology gained widespread adoption in the 2010s, evolving from mountain bike origins in the late 1990s to become standard for gravel and e-bikes by the mid-decade, driven by improvements in rim and tire compatibility. Innovations like hookless rims, which lack traditional bead hooks, have simplified bead seating and reduced manufacturing costs, though they require specific tire approvals for safety at lower pressures (typically max 72 PSI for road use); as of 2025, ongoing safety debates have led some manufacturers to limit or abandon them. Today, tubeless setups dominate performance-oriented cycling, with nearly all new gravel and e-bike models shipping tubeless-ready.

Suspension Mechanisms

Pneumatic Tires

Pneumatic tires, the predominant type used on bicycles, operate on the principle of compressed air providing cushioning through controlled deformation under load. The air, contained either within a separate inner tube or directly between the tire casing and rim, compresses when the wheel encounters obstacles or the rider's weight, absorbing shocks and vibrations to enhance ride comfort. This deformation allows the tire to conform to uneven surfaces, distributing pressure and maintaining traction while minimizing energy loss from rigid impacts. The compliance of pneumatic tires arises from their ability to deflect typically 10-20% under typical rider loads, which effectively dampens road irregularities. This deflection is governed by the interplay of air volume and inflation pressure, following Boyle's law, where pressure and volume are inversely proportional for a fixed amount of gas at constant temperature (PV = constant). As the tire deforms, the air volume decreases slightly, increasing internal pressure to resist further compression and return the tire to its original shape, thereby contributing the vast majority of the overall vertical compliance in a bicycle wheel system. In the tubed variant, common in budget clincher tires, a separate inflatable rubber inner tube is seated inside the outer casing and inflated to hold the air. This design is straightforward and cost-effective, making it prevalent in entry-level bicycles. Ride characteristics vary with inflation: higher pressures result in a stiffer tire with less flex, favoring speed on smooth surfaces by reducing rolling resistance, while lower pressures increase flex for greater comfort on rough terrain, though at the potential cost of higher energy dissipation. Despite their advantages, pneumatic tires have limitations, including vulnerability to punctures from sharp objects that can breach the casing or tube, leading to sudden deflation. Additionally, they experience gradual pressure loss over time, typically 1-2 psi per week due to air permeation through the rubber, necessitating regular reinflation to maintain performance. Tubeless systems represent a subtype of pneumatic tires, where sealant and airtight components hold air directly against the rim without a tube.

Airless and Solid Tires

Solid tires, constructed entirely from rubber without any internal air chamber, have been employed in low-speed utility bicycles for their exceptional durability and resistance to punctures. These tires eliminate the risk of deflation, making them suitable for applications where reliability is paramount, such as delivery or industrial bikes, though they offer a notably harsh ride due to the absence of compliance from air cushioning. Airless tire designs represent a more advanced alternative, incorporating mechanical or flexible structures to mimic suspension without relying on inflation. For instance, the Michelin X Tweel features radial polyurethane spokes that provide flex for shock absorption, functioning as a single integrated wheel unit. Similarly, systems like those from Tannus utilize patented Aither foam technology with segmented, flexible webs to achieve compliance through material deformation rather than air. In November 2024, Supreme Dutch launched an improved airless tire with a robust micro-cell structure for enhanced durability in urban mobility applications. These innovations, emerging prominently after 2010, aim to balance puncture resistance with improved ride quality over traditional solid rubber. Key advantages of airless and solid tires include complete puncture-proof construction, eliminating the need for inflation or ongoing maintenance, which enhances reliability for urban commuting and heavy-load scenarios. They have gained adoption in e-bikes and cargo bicycles, where downtime from flats is costly, with prototypes like the Michelin Tweel specifically developed for e-cargo trikes to maximize uptime. However, these tires exhibit higher rolling resistance compared to pneumatic options, typically requiring 5-15% more effort for propulsion based on user reports. Additionally, they are typically heavier than equivalent pneumatic tires, though the difference varies by model (e.g., negligible for some like Tannus). In applications, airless and solid tires are increasingly used in urban e-bikes, cargo setups, and fat bike variants for their maintenance-free benefits, supporting standards for non-pneumatic bicycle mobility in diverse terrains.

Variations and Special Features

Puncture Protection

Puncture protection in bicycle tires encompasses a range of material and structural enhancements designed to prevent or mitigate punctures and cuts in pneumatic tires, primarily by blocking or sealing small penetrations from thorns, glass, debris, or sharp blades. These technologies are essential for urban commuting, touring, and off-road riding, where flat tires can disrupt travel. Common approaches include internal liners, puncture belts, thick protective inserts, and fluid sealants, each balancing protection against added weight and performance impacts. In urban environments, bicycle tires are sometimes subjected to deliberate vandalism involving slashing or cutting with knives or other sharp objects. Certain tires therefore incorporate enhanced cut-resistant features to deter such intentional damage in addition to accidental punctures. These include densely woven high-tech fiber belts (such as Vectran or aramid), thick protective rubber layers, and reinforced sidewalls. While no tire is completely impervious to severe or determined damage, these enhancements significantly reduce the risk and severity of slash-induced failures. Examples include Schwalbe's V-Guard, which employs highly cut-resistant Vectran fibers due to their dense weaving, and thick inserts like the 5 mm SmartGuard in the Schwalbe Marathon Plus, which provides comprehensive resistance to penetration and cutting. Layered defenses often involve liner strips placed inside the tire casing to impede object penetration. Butyl rubber liners, such as those in some aftermarket products, provide a flexible barrier that resists slow leaks from sharp objects like thorns, though they may add friction against the inner tube. Kevlar-based liners, like the Panaracer FlatAway, use densely woven aramid fibers to offer superior cut resistance; tests show they achieve puncture scores of around 126 points in standardized resistance evaluations, effectively blocking penetrations up to several millimeters. These liners typically add 20-30 grams per tire but can increase rolling resistance by up to 14 watts at typical speeds. Puncture belts integrated into the casing provide another key layer of defense, using high-strength fibers woven beneath the tread. Materials like Vectran or aramid (similar to Kevlar) form dense, lightweight belts that stop sharp objects from reaching the inner tube; for instance, Continental's Safety System employs nylon fibers for cut protection with minimal weight penalty. Schwalbe's V-Guard uses Vectran fibers, which are highly cut-resistant due to their dense weaving, in high-TPI casings (e.g., 127 TPI), reducing puncture risk compared to standard tires while adding only 20-40 grams. These belts are particularly effective against urban debris and trail hazards, with urban-oriented tires often rated at protection levels 4-5 and trail versions at 6-7. Fluid sealants offer a reactive defense, consisting of latex-based liquids that coagulate upon contact with air through a puncture. Pre-applied in tubeless setups or injected into tubes, products like Schwalbe's Doc Blue seal holes up to 3 mm in diameter by forming a plug as the wheel rotates, with effectiveness lasting 2,000 km or 2-7 months. These sealants are most reliable for small punctures from thorns or staples, though they struggle with larger cuts over 6 mm. Integration with tubeless systems enhances this by allowing immediate self-sealing without tube damage. Thickened casings combine high thread-per-inch (TPI) weaves with embedded protection layers for comprehensive defense. Tires like Schwalbe's Marathon Plus use 5 mm SmartGuard rubber inserts in a 67 TPI casing, providing "flat-less" performance (Protection Level 7) that withstands thumbtacks and glass shards, ideal for urban and light trail use. This approach can add 40-50 grams per tire but halves puncture incidence in abrasive conditions. Tire integrity standards, such as ISO 5775 for overall dimensions and compatibility, indirectly support puncture resistance by ensuring proper fit and pressure retention, though specific protection ratings come from manufacturers like Schwalbe and Continental, which define levels from 1 (basic) to 7 (maximum) based on penetration resistance. Urban tires typically achieve 5 mm protection, while trail models extend to 10 mm. These enhancements involve trade-offs, as added materials increase weight by 20-50 grams, potentially raising rolling resistance by 5-10% or 2-5 watts at 25 km/h, which can affect speed and efficiency on smooth roads. Riders must select based on terrain, prioritizing lighter belts for racing and heavier inserts for commuting.

Specialized Treads and Surfaces

Studded tires feature metal or rubber pins embedded in the tread to enhance grip on icy and snowy surfaces, providing superior traction compared to standard winter tires in such conditions. These pins dig into ice, improving control during braking and cornering, though they are less effective on dry pavement where they can reduce traction slightly. Drawbacks include increased noise and vibration on hard surfaces, as well as faster wear when used outside winter environments. Legality varies by region, with some areas permitting their use only during winter months to minimize road damage. For indoor training on stationary rollers or wheel-on trainers, specialized tires use smooth, high-grip rubber compounds designed to resist slippage against the drum or roller surface. These tires feature a slick tread that maximizes contact area, reducing noise and ensuring stable power transfer during high-intensity sessions, while their heat-resistant materials withstand prolonged friction without degrading. Unlike road tires, they prioritize durability over rolling efficiency on pavement, often lasting thousands of miles in controlled indoor use. Off-road variants incorporate directional knobs arranged to facilitate mud and sand evacuation, allowing the tire to self-clean as it rotates and maintain consistent traction in loose terrain. Tapered or ramped knob designs, thicker at the base and narrower at the top, further aid in shedding debris during wet or muddy conditions, preventing clogging and preserving grip. For gravel riding, semi-slick patterns feature a low-profile center tread for efficient rolling on hardpack, complemented by raised shoulder lugs that engage during cornering to provide lateral stability without excessive drag. Urban commuting tires often include deep grooves in the tread pattern to channel water away, improving drainage and reducing hydroplaning risk on wet city streets. Many incorporate reflective strips or sidewalls for enhanced visibility in low-light conditions, increasing cyclist safety alongside their puncture-resistant construction suited for mixed pavement and light gravel. These designs balance wet-weather performance with everyday durability, making them ideal for daily rides in variable urban environments. Customization options in the 2020s include modular systems with interchangeable treads, such as zipper-based designs that allow users to attach different tread "skins" to a base tire for adapting to changing conditions like rain or off-road paths. These experimental prototypes, developed for quick swaps in seconds, promote versatility and reduce waste by reusing the core tire structure across multiple tread types.

Aerodynamic and Reflective Options

Aerodynamic designs in bicycle tires prioritize reducing air resistance through streamlined profiles, particularly for high-speed road and time trial applications. Low-profile sidewalls and minimal or slick treads minimize turbulence and yaw-induced drag, with textured tire surfaces achieving up to an 8% reduction in aerodynamic drag compared to smooth tires during wind tunnel testing at yaw angles simulating crosswinds. For instance, the Continental Aero 111 tire incorporates vortex generators in its tread to optimize airflow, claiming a potential savings of up to 18 watts in drag at racing speeds, though this comes at the cost of slightly higher rolling resistance. These features are especially prevalent in time trial-specific tires like the Vittoria Corsa Pro Speed and Continental GP5000 TT TR, which use near-slick patterns to enhance efficiency above 30 km/h on paved surfaces. Reflective elements integrated into bicycle tires improve nighttime and low-visibility safety by enhancing detectability from motor vehicle headlights. Many urban and hybrid tires feature reflective sidewalls or tread lines using specialized paints or strips that reflect light without compromising structural integrity, such as the Bontrager H2 Hard-Case Ultimate and Schwalbe Marathon series. These designs comply with U.S. Consumer Product Safety Commission (CPSC) standards under 16 CFR 1512.16, which mandate reflective devices for bicycle recognition and identification, allowing tire-integrated reflectors to contribute to overall visibility requirements alongside pedal and frame reflectors. While glass beads are commonly embedded in road markings for retroreflectivity, tire manufacturers employ similar prismatic or phosphorescent materials in sidewalls to achieve comparable effects for rider safety in compliance with these regulations. Lightweight aerodynamic tires for racing often employ thin casings and advanced rubber compounds to balance speed and durability, with weights typically under 200 grams per tire in 25c sizes. Examples include the Vittoria Corsa Pro, weighing around 185 grams, which uses a graphene-infused compound for reduced rolling resistance while maintaining aero-optimized sidewalls. These designs prioritize minimal material in the casing to lower rotational mass, aiding acceleration in competitive scenarios without sacrificing puncture resistance through layered aramid belts. In certain e-bike configurations, front and rear tires differ to optimize steering and load distribution, with narrower front tires (e.g., 1.75-2.0 inches) enhancing maneuverability and aerodynamics, while wider rear tires (e.g., 2.5-3.0 inches) provide greater stability under the added weight of batteries and motors. This setup improves handling on urban roads by reducing front-end drag for quicker turns and bolstering rear traction for stability during acceleration. Self-inflating tire prototypes, emerging from 2020s research, incorporate micro-pumps or hub-integrated systems to maintain optimal pressure dynamically, drawing from ambient air or compressed reservoirs via electronically controlled valves. Systems like Gravaa's adjustable pressure technology use on-board sensors and Presta-compatible valves to inflate or deflate tires on the fly, potentially saving 25-30 watts on rough terrain by adapting pressure without stopping. These experimental designs, tested in professional events like the UCI Gravel World Championships, address pressure loss from punctures or terrain changes but add about 250 grams per wheel due to the mechanical components.

Sizing and Standards

Tire Dimensions and Categories

Bicycle tire dimensions are primarily defined by the International Organization for Standardization (ISO) under standard 5775, which adopts the European Tyre and Rim Technical Organisation (ETRTO) system for precise measurement and compatibility. The ETRTO notation specifies tire size as width in millimeters followed by the bead seat diameter (BSD) in millimeters, such as 23-622, where 23 mm is the nominal tire width and 622 mm is the inner rim diameter on which the tire bead seats. This system ensures global consistency in tire-rim matching, having become the international standard since its formal adoption in the 1990s. Legacy sizing systems persist in some markets, particularly for older or regional bicycles. The French system, common for road tires, uses an approximate outer diameter in millimeters (e.g., 700) followed by width in millimeters and a letter code (e.g., 700x25C), where "C" indicates a standard width category; this approximates the ETRTO equivalent of 25-622. Inch-based notations, prevalent in North American mountain biking and BMX, denote approximate outer diameters in inches with fractional widths (e.g., 26 x 2.0), often corresponding to ETRTO sizes like 50-559 for a 26-inch wheel. Tire categories are classified by width to suit specific riding conditions, balancing speed, comfort, and traction. Lightweight tires, typically 18-25 mm wide, are designed for road racing, prioritizing low rolling resistance and aerodynamics on paved surfaces. Middleweight tires, ranging from 26-35 mm, serve hybrid and touring bikes, offering versatility for mixed urban and light off-road use with moderate cushioning. Balloon tires, measuring 35-44 mm, appear on cruiser bicycles for a plush ride on smooth paths, emphasizing style and shock absorption over speed. Plus-size tires, 40-50 mm wide, cater to gravel and adventure cycling, providing enhanced grip and compliance on rough terrain without excessive bulk. Fat tires exceed 65 mm (typically 3-5 inches or 76-127 mm), used on snow bikes and trail machines for superior flotation and stability in loose or soft conditions like sand and snow. Common diameter standards vary by bicycle type to optimize performance. Road bikes typically use 700c wheels with a 622 mm BSD for efficient rolling on highways. Mountain bikes employ 26-inch (559 mm BSD), 27.5-inch (584 mm BSD), or 29-inch (622 mm BSD) diameters, with larger sizes improving rollover on obstacles. BMX bicycles standardize on 20-inch (406 mm BSD) wheels for agility in tricks and jumps. The aspect ratio, or width relative to diameter, influences tire stability by affecting the contact patch and center of gravity; narrower profiles on larger diameters enhance speed but reduce balance, while wider tires on the same diameter broaden the base for better handling in challenging environments. For instance, fat tires with widths of 3-5 inches (76-127 mm) demand frame clearances of at least that magnitude to prevent rubbing and ensure safe operation. Larger tires also allow for adjusted inflation pressures to maintain ride quality across sizes.

Rim Compatibility

Bicycle tire and rim compatibility primarily revolves around ensuring a secure interface that prevents slippage, blow-offs, or instability during use. The European Tyre and Rim Technical Organisation (ETRTO) establishes standards for width pairings to achieve this, recommending that the internal rim width be approximately 0.7 to 0.9 times the tire width for optimal fit and performance. For instance, a 25 mm tire pairs safely with rims having internal widths of 17 mm to 23 mm, allowing the tire to seat properly without excessive ballooning or pinching. For 30 mm road bike tires, an internal rim width of 23-25 mm with hooked beads is ideal for optimal compatibility, safety, grip, comfort, and aerodynamics. These guidelines help maintain structural integrity and can influence handling characteristics, such as cornering stability, though detailed effects are covered elsewhere. As of 2024, there have been debates and UCI advisories emphasizing strict adherence to ETRTO compatibility guidelines for hookless systems to ensure safety. Rims differ in design based on tire type and mounting system, with hooked and hookless variants serving distinct roles. Hooked rims, featuring a protruding lip on the inner wall, are suited for high-pressure clincher tires, providing mechanical retention for the bead even at inflation levels exceeding 100 psi. Hookless rims, by contrast, use straight sidewalls and are primarily designed for tubeless setups, where the tire bead forms a friction-based seal; ETRTO guidelines limit their use to a maximum pressure of 72.5 psi (5 bar) to mitigate risks of tire unseating. Additionally, rims for tubular tires feature a smooth, flat bed optimized for adhesive bonding, differing from clincher rims' hooked or straight profiles; while some multi-use rims attempt versatility across tire types, dedicated designs ensure better reliability and are preferred in professional applications. Effective bead seating is fundamental to compatibility, requiring the tire's bead diameter to precisely match the rim's shoulder diameter as defined by ETRTO specifications, typically denoted in the rim's ETRTO marking (e.g., 622 mm for standard road rims). A mismatch, such as using a tire with a larger bead on a narrower rim profile, can prevent full seating and lead to catastrophic blow-offs under centrifugal force or impact. To verify retention, CEN and ISO standards (e.g., ISO 4210-2 for bicycle safety) mandate rigorous testing, including falling mass impact tests with a 23 kg mass dropped from 360 mm to simulate real-world stresses like potholes or curbs, ensuring the tire remains securely attached without dislodging.

Performance Parameters

Inflation Pressure Effects

The inflation pressure of a bicycle tire significantly influences its performance, safety, and longevity, with optimal ranges varying by tire type and rider load. For road bicycle tires, pressures typically fall between 80 and 120 psi to balance rolling resistance, comfort, and puncture resistance, while mountain bike tires operate at lower pressures of 20 to 50 psi to enhance traction and absorb terrain impacts. These values are determined using load tables that account for the total system weight, including rider, bicycle, and any cargo; for instance, a 70 kg rider on a 25 mm road tire might require around 90 psi to maintain proper contact patch and avoid excessive deformation under load. Environmental factors can alter tire pressure post-inflation, necessitating adjustments for consistent behavior. Temperature changes affect pressure according to the ideal gas law approximation P∝TP \propto T, where pressure rises approximately 1 psi for every 5°C increase in air temperature, as the gas inside the tire expands; conversely, cooling contracts it, so pressures should be checked and set when tires are cold to avoid over- or under-inflation during use. Altitude also impacts gauge pressure due to reduced atmospheric pressure at higher elevations, causing an approximate 0.5 to 1 psi increase per 300 m gain, as the internal absolute pressure remains constant while external pressure drops. Improper inflation exerts undue stress on the tire carcass, compromising structural integrity. Overinflation beyond the maximum psi marked on the sidewall strains the tire's fabric and rubber, increasing the risk of blowouts from sidewall failure under impact or heat buildup. Underinflation, meanwhile, heightens vulnerability to pinch flats, where the inner tube is compressed between the rim and tire casing upon hitting obstacles, often resulting in paired punctures. Accurate monitoring is essential to mitigate these effects, with digital gauges offering precision to within 0.5 psi compared to traditional analog tools' broader margins of error. Smartphone apps further aid by providing load-based recommendations tailored to rider weight, tire width, and conditions, helping cyclists calculate and maintain optimal pressures dynamically.

Load and Force Dynamics

Bicycle tires primarily support the vertical gravitational load exerted by the combined mass of the rider, bicycle, and any cargo, given by the force F=mgF = m g, where mm is the total mass and g≈9.81 m/s2g \approx 9.81 \, \mathrm{m/s^2} is the acceleration due to gravity. For a typical system mass of 80 kg (e.g., 70 kg rider plus 10 kg bicycle), this vertical force amounts to approximately 785 N, distributed between the front and rear tires. This load is transmitted to the ground through the tire's contact patch, where the average pressure PP relates to the patch area AA by A=F/PA = F / P, ensuring the tire deforms sufficiently to maintain contact without excessive stress. The contact patch forms an elongated, roughly rectangular or elliptical shape due to the tire's curvature and deflection under load, with a typical length of 50–100 mm along the direction of travel and a width approximately equal to the tire's tread width (e.g., 25–35 mm for road tires). The area of this patch scales with the tire's vertical deflection, increasing as load rises or pressure decreases, which helps distribute the force evenly and influences grip and stability. For instance, under a 340 N load at 3.5 bar inflation, the patch area is measurable via axis lengths, showing about 12% larger dimensions on flat surfaces compared to curved test drums. In a standard bicycle, the vertical load is distributed between the front and rear tires, typically around 40% on the front and 60% on the rear under static or cruising conditions; during braking, dynamic weight transfer shifts more load forward, often to a 60/40 split favoring the front tire, enhancing braking effectiveness but requiring careful balance to avoid rear wheel lift. In tandem bicycles with multiple riders, the load is shared across four contact patches (two per axle), reducing deflection per tire and altering overall equilibrium dynamics compared to single-rider setups. Static equilibrium under vertical load is maintained by the tire's radial stiffness kk (in N/mm), which resists deflection δ\delta according to δ=F/k\delta = F / k; measured values for bicycle tires range from 31 N/mm to 147 N/mm depending on size, pressure, and construction, with typical deflections of 3.5–6 mm under 340–659 N loads. Higher stiffness reduces deflection for a given force, improving efficiency but potentially harshness, while lower stiffness allows greater compliance for comfort. Exceeding a tire's load rating, such as over 100 kg (approximately 980 N) per tire—common for narrower road tires rated around 110 kg maximum—can lead to excessive sidewall deflection, accelerated wear, or structural failure, particularly under repeated dynamic stresses. Manufacturers specify these limits based on tire construction and pressure, with wider tires (e.g., 38 mm) supporting up to 150 kg to accommodate heavier loads safely.

Rolling Resistance and Handling

Rolling resistance in bicycle tires primarily arises from hysteresis loss in the rubber compound, where energy is dissipated as heat during the deformation and recovery of the tire as it rolls over the ground. This loss is quantified by the coefficient of rolling resistance, denoted as CrrC_{rr}, which typically ranges from 0.002 to 0.008 for high-performance road bike tires on smooth surfaces. The rolling resistance force is calculated as Frr=Crr×FverticalF_{rr} = C_{rr} \times F_{vertical}, where FverticalF_{vertical} is the vertical load on the tire; this force opposes forward motion and can account for 5-10% of total power expenditure at typical cycling speeds. Supple tire casings, featuring thin, flexible sidewalls and low-denier fabrics, minimize CrrC_{rr} by reducing internal friction during deformation, often achieving values as low as 0.003 in optimized setups. Several factors influence rolling resistance beyond the basic coefficient. Tread compounds play a key role, with softer, grippier rubbers exhibiting higher hysteresis and thus elevated CrrC_{rr} compared to harder, faster-rolling formulations that prioritize speed over traction. Inflation pressure affects deflection at the contact patch, with optimal performance occurring at levels allowing 10-20% tire sag under load, balancing minimal deformation losses against excessive sidewall bulge. Surface conditions further modulate resistance, as smooth pavement yields lower CrrC_{rr} (around 0.004) than rough gravel or dirt, where deformation increases by up to 50%. In terms of handling, bicycle tires generate cornering force through lateral friction, with the coefficient μ\mu ranging from 0.8 to 1.0 on dry asphalt, enabling safe negotiation of turns up to 0.9g lateral acceleration before slip. Camber thrust emerges when the tire leans into a corner, deforming the carcass asymmetrically to produce a lateral force that contributes to the restoring moment M=Flateral×hM = F_{lateral} \times h, where hh approximates the effective height of the force application above the contact patch; this self-stabilizing effect aids balance at lean angles of 20-45 degrees. Tires also influence dynamic moments, such as pitch during braking—where sidewall compression absorbs forward dive—and yaw from steering inputs, with flexible sidewalls enhancing responsiveness by contributing 20-30% to the overall handling feel through subtle compliance. Testing methods standardize these parameters for comparison. Coast-down tests measure CrrC_{rr} by timing deceleration on a level surface, isolating tire losses after accounting for aerodynamics and inertia, often yielding results within 5% of lab drum data. For peak grip, protocols adapted from SAE J1269 evaluate lateral force on rotating drums, assessing μ\mu under controlled slip angles to quantify cornering limits.

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  160. https://www.renehersecycles.com/the-science-behind-the-tire-pressure-calculator/
  161. https://www.sciencedirect.com/science/article/pii/S0165232X2100063X
  162. https://physicalcycling.com/tire-traction/
  163. https://www.thecontactpatch.com/road/c0415-cornering-basics
  164. https://motochassis.com/articles/tyres-and-how-they-work/
  165. https://www.sae.org/papers/tire-rolling-resistance-measurements-coast-tests-760153
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