Do Lower Profile Tires affect Speedometer Reading

[Huw Powell]

>> The reason you go to a narrower tire in the winter is actually quite
>>simple. PSI. Yes, pounds per square inch. The weight of the
>>vehicle (or the
>>transferred weight if the body is in motion) divided by the
>>contact patch of
>>the tire. A narrower tire has a smaller contact patch and therefore the
>>edges on a snow tire (siping and tread) have more force to "bite" into the
>>surface. 

> Are you absolutely sure that the contact patch total area is determined
> simply by the width of the tire and not at all related to air pressure
> (hmm...measured in PSI) in the tire? (Within the limits of the tire carcass
> stiffness.) Narrower/different shape contact patch, sure, but actually
> smaller without changing air pressure, I don't think so.

That is correct.  The PSI (or kg/cm^2) in the tires exactly corresponds 
to the weight of the car/contact area ratio.  As long as they aren't 
flat and on the rims, then all bets are off.

Of course, a long, narrow patch will bring more of the edge of the tire 
into contact with the road than a short, wide one...

-- 
Huw Powell

http://www.humanspeakers.com/audi

http://www.humanthoughts.org/