Forward Traction

[TnBlkC230WZ]

I posted this response in the suspension thread, but I thought a new thread in "tires" would be better. I'm want to know why low profile tires limit forward traction.

What impact do low profile tires have on forward traction? First I've heared of this. I want straight line traction, but good handling is a must. (I'm and autocross fan) I was considering 255/45-18s as well. Could go with a 235/55-17 or even a 255/60-15. Problem with the 15s are the lack of high performance tires. I would like a 26.5 - 27 inch tire on the rear and a 25.5 - 26 inch on the front.

I'll be running Hotchkis springs and shocks as well with a 355 HP ZZ4 and a 3.73 posi rear.

[MrQuick]

you can always compensate with a wider tire with good compound. I see 315/17's in your future.

[NOT A TA]

I tried my 315 17's Yokohaha AO32's at the strip and they just lite up and the 60' time is slow. I use MT ET streets 15" that are about 26" tall and have a Hotchkis / Bilstein setup. No traction probs off the line using my 3.73 rear in my Firebird.

John

[TnBlkC230WZ]

I don't think 315's will ever clear. I thought the ET streets are street legal drag tires. Will they work on a road coars? Am I trying to have my cake and eat it too?

Edit - Ok, there are Sportsman SRs. Will they work on a road coarse?

[NOT A TA]

ET streets are bias ply DOT legal drag tires. They will not work well for road course activities. I use them for Drags and around town with 3.73 rear. I have the Yokohama 17's for road course open track and high speed events as well as highway driving and use a 2.72 or 2.41 rear with them. I decided I couldn't have my cake and eat it so I have a couple setups to choose from. I sold my 255's after deciding they would be a comprimise for the varied events I like to attend. I've nener tried the Sportsman SRs.

John

[TnBlkC230WZ]

Maintaining two sets of tires is doable, but swaping rear gears would be a pain. I wouldn't mind having 2.72s for cruising.

[DarkoNova]

It's mainly because of the sidewall (or lack thereof). Well, aside from the actual compound and tread pattern. The tall sidewall of a typical 15" wheel helps flex a bit under straight line acceleration. Low profile tires have next to nothing for a sidewall, so they transmit the turning motion instantly. The lack of much sidewall is good for handling, though, as it creates a stiffer tire that doesn't flex. There was a video a while back that had a funny car launching, but it was in slow motion, and you could see the tire wrap up. Pretty neat.

Matt

[TnBlkC230WZ]

I've seen images of wrinkle wall tire flex. It's pretty neat to watch. I guess it is storing the energy to be released further down the track when it can be used.

[Boesch]

It's mainly because of the sidewall (or lack thereof). Well, aside from the actual compound and tread pattern. The tall sidewall of a typical 15" wheel helps flex a bit under straight line acceleration. Low profile tires have next to nothing for a sidewall, so they transmit the turning motion instantly. The lack of much sidewall is good for handling, though, as it creates a stiffer tire that doesn't flex. There was a video a while back that had a funny car launching, but it was in slow motion, and you could see the tire wrap up. Pretty neat.

Matt

This is a great explanation and Matt has hit the nail on the head. This is the exact reason that all top fuel dragsters run such small diameter wheels on the back. Take a look at how much side wall flex there are on those tires, you can see it as they sit at the line. That's just the same difference you'll see with low profile tires and 15" tires, just magnified.

So from an engineering standpoint this means that you have a slightly delayed reaction between the axle twisting and the tire rotating on the ground. This leaves enough time for the tire to start rotating just a tad slower which helps it to maintain traction. Without the delay the tire accelerates so fast that it can not maintain traction. I think we all understand how fast you get going when you're spinning.