Contour Enthusiasts Group Archives Forums Modifications Duratec Performance Its been a while

I think both sides of the argument are correct here, you just don't realize that you're arguing two different points.

True, friction is simply the "normal" force times the coefficient of friction. (Normal force meaning the force perpendicular to the contact surface - in this case the normal force is the gravity times mass). And true, it takes the same amount of force to slide a box on its wide side as it does to slide it on its narrow side, since friction has nothing to do with surface area.

However, this does not stand up very well when you get to deformable objects like a tire. A road surface, no matter how smooth, is actually made up of a lot of peaks, valleys, points and divots. A tire is able to deflect and confom to these irregularities, whereas a box simply rides on top of them. To accerate the car then, the tire is not relying only on the friction force between the tire and the road, but also on the fact that it is able to mesh with these irregularities, almost like two gears meshing, and "push off" of the irregularities helping the car to move forward. A wider tire has more irregularities to "push off" of, and thus can provide more traction to accelerate the car either in a straight line, or while cornering. Granted, most of the acceleratory (is that a real word?) force is from friction, but much of it comes from the tire pushing against the irregularities.

At least that's my theory on it.

And from the "Ask A Scientist" and the explanation that merely increasing the contact area will increase the force required to slip, this holds up for the tires if you apply my above explanation to the problem, it does not hold up for the box, whether you believe my explanation or not. The only thing that governs when the box will start slipping is if the force pushing the box exceeds the force of gravity multiplied by the mass of the box multiplied by the coefficient of fricton.

The only thing in this thread that I think is just wrong is arguing that top fuel racers use wider tires because they are heavier, which in turn gives better traction. If a drag racer wanted to increase traction by adding weight, he would simply add some weight over the driven axle, not use heavier tires. A heavier tire would have a have a higher rotational inertia than a lighter tire, making it more difficult to accelerate. Not to mention that adding weight to a dragster is a ridiculous idea.

Bob

Then why do they have classes for different tire width if wider does not garner better traction? (ever talk to a pro-street racer?)

Tires only "balloon" at speed; once they are rotating, not initially.
To be "factual" they actually decrease in diameter initially as the sidewall wrinkles...

Crossdrilled rotors are Lighter! less rotating mass is easier to stop then more. The holes marginally help vent gas at best (when the pads are over them they are Sealed! - Slotting rotors is for venting gas!)
Oh and BTW - yes less surface contact would mean less friction and less stopping power. The other benefits of the design just out weigh this fact. (gas venting alone makes for faster stopping! No gas build-up pushing back on pads!)

Remember what I said last post... :rolleyes:

Maybe this will help with the original question...searched the coldair archives, bnoon posted this May 2000:

"Borrowed a set of 225/50/15 BFG drag radials this spring, couldn't get a
good launch and that scared me (and my differential). I went back to my
Potenzas and ran .3 better. Also, ever have wheel hop coming out of a burn
out box? Not funny. Unless you have no wheel hop, or have a Quaife, stay
away from to much improved traction on these cars."


http://www.coldair.org/archives/0005/msg01637.html

Ahem... I never said I had the right answer, I merely pointed out somehting that was not mentioned... As for being way behind.. LMAO.. read my post again, and then the ask a Prof,and Bob H's responses.

as far as the force translation... That isn' t the topic at hand, so i didnt feel it relevant.. Yes many things serve more than one purpose... Ie the Holes on your cross drilled rotor that you keep mentioning(aargH the guy who brought that one up on this topic thread anywayshould be shot!! LOL.. he was totally off), they too serve more than one purpose... reduced mass, increased cooling(IE larger surface area to dissapate heat from, venting, making you spend aLOT of money to get new rotors everytime yours warp because most places can't turn a Cross-drilled rotor...LOTSA THINGS)I mean if you want me to go on about EVERThINg a slick does.. I should start with, "keeps rim from contacting the ground" :rolleyes:

ANyways.. good post Bob H... that did it for me...

My first post mentioned PhatSVT is going to use them with a Terry haines modified box (clutch, flywheel, quaife!)

My post was not directed towards you.

Matter of fact we both posted that drag slicks sidewalls "wrinkle". I just did it "behind" you...

ahem..
id go with this

nah, that'd be senior physics

LOL Demon, I live in Austin, TX.. becareful when you say that you do things "behind" me...LOL...

no offense taken.. I came from a list with NAZI-like moderators..LOL Im glad I can kinda actually speak my mind sometimes here..

OMG ContourGuy, quit posting about basic physics and go read a vehicle dynamics book. Read about tire deflection and slip and the "magic formula," then apply your physics to the whole complex system instead of trying to make a simple block and surface interaction fit. There's a reason that tire performance is goverened by a thing called "the magic formula:" it had to be empirically defined because the tire/road interaction is so complex.