Why are bike tires so narrow and large diameter compared to car tires? What tradeoffs are here exactly? Motorcycle and some ebike tires are more similar to car tires than to bike tires, so i guess it has something to do with braking length at maximum expected speed, and probably also with weight of vehicle, as to not exceed some specified pressure on road. There has to be so many more reasons (weight? air resistance? some other things affecting efficiency or safety? ???)

update: apparently friction involving things that are bendy is monstrously complicated subject, and also there are material limits like maximum allowed shear stress

  • Azzu@leminal.space
    4·
    15 hours ago

    While there is no area in the friction equation, in the real world it is nonetheless a factor. You got to remember that a larger area makes it so small patches of lower friction (sand patch or water or trash or whatever) have less of an impact, with more area you have a higher chance to still be in contact with the asphalt. More area also gives more opportunity for the ridges in tires to displace water or grip onto gravel/dirt. While simple contact friction is the same, total friction is not necessarily depending on the conditions.

    • untorquer@quokk.auEnglish
      1·
      13 hours ago

      Responding to:

      More rubber on the road means more grip. As the weight and corner speeds increase, you need more of it.

      However,

      a larger area makes it so small patches of lower friction (sand patch or water or trash or whatever) have less of an impact, with more area you have a higher chance to still be in contact with the asphalt.

      Unless we’re talking about liters of sand/gravel then this fails to explain how motorcycles have as much grip as cars do, as is evidenced by cornering ability.

      More area also gives more opportunity for the ridges in tires to displace water or grip onto gravel/dirt.

      Tread depth and pattern handle these.

      …

      Racing tires are wider because they need to handle higher loads. Racing slicks also maximize contact area to extend tire life and reduce wall thickness. There’s thermal conduction as well. Rubber is an insulator. Rubber friction changes with temperature. So does modulus, leading to more deformation and thus more heating. Too thick rubber makes a hot tire that loses friction coefficient. Too thin and it wears too fast, you’re on steel 3 laps in. so you make it wide enough to distribute the load, reduce stress, and control heating while trading off mass. This is also controlled by chemical composition. After that you’re designing for weather conditions.

      Passenger vehicle tires focus more on climate and adverse road conditions and long life. Because they are much lower performance, they have much lower loads and use tires with less contact area. The same is the case for motorcycles and bicycles.

    • AmidFuror@fedia.io
      1·
      14 hours ago

      This is perhaps an easier to understand explanation:

      https://www.physlink.com/Education/Askexperts/ae140.cfm

      Although a larger area of contact between two surfaces would create a larger source of frictional forces, it also reduces the pressure between the two surfaces for a given force holding them together. Since pressure equals force divided by the area of contact, it works out that the increase in friction generating area is exactly offset by the reduction in pressure; the resulting frictional forces, then, are dependent only on the frictional coefficient of the materials and the FORCE holding them together.

      If you were to increase the force as you increased the area to keep PRESSURE the same, then increasing the area WOULD increase the frictional force between the two surfaces. Answered by: Paul Walorski, B.A. Physics, Part-time Physics Instructor