Contact patch again???

[C M Smith <cmsmith@domain.elided>]

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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