Comment on Why do tires have the width and diameter they do?

Alsjemenou@lemy.nl ⁨1⁩ ⁨day⁩ ago

• untorquer@quokk.au ⁨1⁩ ⁨day⁩ ago

  There is no pressure nor area in the friction equation. ‘Fu=u*Fn’

  Fu - friction force

  u - friction coefficient

  Fn - normal force

  Pencil thin tires of the same material have the same grip as extra wide ones in dry conditions. Tread geometry can change for wet but only to prevent hydroplaning, friction is still the same between the tires fire a given condition.

  More contact area means less stress on the rubber which means the rubber wears less for the same load. A car weighs 2 tons, a bike+rider is less than 100kg/200lb. 1/20 the contact area for similar wear. If a car had bike tires they would probably melt after a few km

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  • Azzu@leminal.space ⁨1⁩ ⁨day⁩ 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. More area also gives more opportunity for the ridges in tires to displace water or grip onto gravel/dirt. While friction is the same, total traction is not.

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    • AmidFuror@fedia.io ⁨1⁩ ⁨day⁩ 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

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    • untorquer@quokk.au ⁨1⁩ ⁨day⁩ 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.

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      • Azzu@leminal.space ⁨22⁩ ⁨hours⁩ ago

        There’s no space for thread pattern if the area is too small.

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