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#16
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Quote:
-mike |
#17
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I thought speed rating had everything to do with simply the tires being able to stand up to all of that centrifugal force (centripetal force? I never remember which one is right)
your lateral acceleration is V^2 / R and if you're going 150mph (67meters / second) and assuming your tires have a stock circumfrence your radius is going to be .315m your lateral acceleration is 14,231 m / s^2 (one G is 9.81 m / s^2) so this is going to be roughly 1400 times as strong a outward force on the tires as gravity exerts on us. The only way that I can think of being able to take this much stress is if they are very light and have very strong re-inforcing materials in them. |
#18
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Abdominal,
You are partially correct in all the things you say. You would be totally correct if the tire operated on a machine that kept it perfecly round as it spun the tire. However, the tire sits on the ground (road) and must deflect to flatten out as the tread touches the groundand rebound as it leaves the ground. There are also side forces on a tire induced by turning and the cars suspension. All this movement generates flexing and squirm. This causes heat because the carcas of a tire is not one homogeneous piece. It is made up of rubber compounds(synthetic), fabric or metal belts, and fabric cords. Also the tire is built up in plys then molded into one piece. All these materials have different coeficients of strength and expansion. Think of the inside of a tire as the layers of lasagna rolled into a circle instead of laying flat. The flexing and squirming that a tire goes through generates heat and rubber is not a good conductor so the heat stays inside the carcas. This internal heat makes the metal, rubber, synthetic fabrics want to expand at different in different rates and in different directions. These pieces try to move in relation to one another. They are not allowed to do this. If they do ...goodbye tire. The faster you go, the quicker the flexing and squirming takes place, and the more internal heat is generated. Therefore, better materials that are stronger and resist heat buildup better are required. That's why, as the speed rating goes up, the tires cost more. This is a very simple general explanation. In reality, it's much more complex.
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