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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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