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Re: Friction

All the physics book tell us that the frictional force is independent of
the
area. One year a student listened to yours truly repeating the idea.
Student
then asks, "Well, if the area doesn't matter, then how come fat tires on
a
race car corner better than skinny tires?"


Being a racer myself, I can tell you that tires don't fit our "area doesn't
matter" discussions.
There are SOOO many variables involved besides contact patch. I once
contacted a tire engineer (they have a special name I've forgotten) and I
was amazed at how complex tires are.
The first thing that popped into my head is the issue of heat. As a tire
warms up it's coef of friction increases then starts to decrease again. My
race tires are optimum at approx 180 deg F. It's very easy to tell when
they're cold and when they're overheating...less grip. A wider tire will
take a little longer to come up to optimal temp than a narrower one, but the
narrow tire will quickly overheat. If you overheat a tire and it will
quickly vulcanize the rubber and become very very hard...and thus not bite
into the track. Tires need to stay soft so some of the rubber actually
tears from the tire to produce best grip. Watch an IndyCar race and look in
the corners. You'll see lots of rubber on the outside of the turn (called
marbles). You'll also notice they do a lot of side to side swerving at the
start of a race..this is to get the tires up to temp. FYI: Indycars go
through around $20,000 in tires for a race.
Dragsters do those cool burnouts for 2 reasons. First to lay down rubber
into the track (rubber on rubber is better than rubber on asphalt) and
secondly to bring those monstrous tires up to temp. FYI: dragster tires
have only 5-10 psi in them...and the top fuel cars burn through 15gal of
fuel per run!!
Your best bet to try and contact an engineer at Goodyear, BFGoodrich or
Firestone and see if they have basic info on tires they'd share with ya.

Jason
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Jason (and Kim and Jacob) Powell
Kenosha, WI
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Physics Dept
Zion Benton HS
Zion, IL
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'96 Red Miata[PEP]...FIZZX 1
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"...the truth the symbol of a dove, will unmask the maker of your plans..."
King's X - Out of the Silent Planet
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