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Contact patch again???



Tire pressure affects contact patch size in proportion to vehicle weight. if it did not, then the vehicle would sit on flat tires. The tire pressure does indeed exert itself in all directions, including upwards to match the force of gravity on the vehicle.

Funniest of all is the knowledge that contact patch area does not affect tire grip. The coefficient of friction operates proportionally to pressure on the contact patch and the area thereof, with one variable going up while the other goes down. So, wider tires do not grip better because of anything that happens to the size of the contact patch. Only the shape changes. Grip changes primarily because of the slip angle effects due to tire carcass design, nothing to do with contact patch shape except incidentally. Lower profile tires of the same rolling radius will have shorter wider contact patches of approximately the same are as those of taller tires on the same vehicle. The additional grip afforded by wider tires is due to shorter stiffer sidewalls. If you don't change the suspension geometry or the tread compound, you won't get much performance increase solely from lower profile tires.

Wheel/tire weight is very important to handling and grip as the shocks and springs can do a better job of keeping the pressure of the contact patch more uniform or progressive.

One interesting tidbit is that bigger wheels generally contribute to heavier wheel tire combos for the same size rolling radius. This is intuitively obvious if one remembers that air weighs nothing. Bigger tires have more air. Lower profile tires are generally smaller than lower profile tires of the same rolling radius, heat up more, and are lighter than the taller tires. But the wheels are heavier, and the gain in wheel weight is more than the savings in tire weight.

Off we go again.

Cheers



Michael Smith
White 1991 164L
Original owner
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