Bicycle tire
(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".
Racers quickly adopted the pneumatic tire for the increase in speed and ride quality it enabled.
These tires have a steel wire or Kevlar fiber bead that interlocks with flanges inside of the rim.
This allows higher (80–150 psi or 6–10 bar) air pressures than was possible older wired-on tires.
Typical tubeless tires have airtight sidewalls and beads which are designed to maximize the seal between the tyre and the wheel rim.
[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.
[14] Tubeless tires are primarily used on mountain bikes due to their ability to use low air pressure for better traction without getting pinch flats.
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.
Although modern airless tires are better than early ones, most give a rough ride and may damage the wheel or bicycle.
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 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.
[36] 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.
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.
[45] 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.
[49] 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.
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.
Examples include the Stanningley (UK)-made Bootie Folding Bicycle, the Co-operative Wholesale Society (CWS) Commuter, and the Trusty Spacemaster.
[69] 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.
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.
[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.
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: 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.
The vertical force generated by a bicycle tire is approximately equal to the product of inflation pressure and contact patch area.
[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] 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.
