I need some help with tire wear at the track...

[IndyDave]

First a bit of background - I have a 2001 Z06 with stock engine, tranny cooler, Carbotech XP10/XP9 pads, CCW T1 wheels (17"x10" front and 17"x11" rear) with what were new 315/35/17 Kumho V700's all around. I recently completed a three day open lapping event at Putnam Park Road Course. I started on Friday with the following alignment:

Front camber -1.5
Front caster max possible without sacrificing camber setting
Front toe out of roughly 1/16"

Rear camber -1.0
Rear to in of roughly 1/8"

The ambient temp got up to about 70 F and I had two sessions where I got into 1:19 lap times (faster than most everyone out there). Putnam is a 10-turn, 1.8 mile road course with nice asphalt pavement.

After seeing what I considered to be excessive tire wear on the outside edges of my front tires, I had the front camber bumped from -1.5 to -2.5.

My tire pressures when warm were getting up to 42 degrees F. The roll to the outside (sidewall) of the tire looked OK. It didn't look to me like I needed a different tire pressure.

The picture below is a shot of the front left tire. At Putnam, 8 of the 10 turns are right-handers, so the front left takes most of the abuse. This shot is like you are looking at the front left (driver's side) looking towards the front of the car. You can see that the outside edge of the tire was still showing much more wear than the inside.



Should I get more negative camber? You can see that the inside of the tire surface has an accumulation of "marbles" from the track, and no, I didn't pick these up as I was coming in to the pits.

Clearly the inside surface of the tire is not being worn like the outside. Is this normal? What changes should I try?

My next track event is Memorial Day weekend at Mid-Ohio. I have time to get a different setup if I figure out what I want to try.

Thanks for the help!

[tigerdrvr]

What pressure were you starting at?
The Kumhos should be able to live at -1.5 with no problems.

[wtknght1]

Live at -1.5 yes...optimal tire wear at -1.5 NO. The T1 guys run camber plates on the front which gets us somewhere around -3 to -3.5 degrees of neg camber...and that's still not enough.

Since your car is mostly stock and you drive it on the street too (I assume) then you have to make a decision between optimal track performance vs tire wear and street driving.
-2.5 in the front for a car that's driven on the street too is more than enough...but you are not going to get optimal tire wear on the track - everything's a compromise.

The wear actually doesn't look too bad because the outside part of the Victoracer has shallower grooves than the inside part of the tire. You simply wore the grooves off the outside and are down to the 'slick' rubber part which is basically the best part of the tire anyway.

You may be able to help this situation by having them shaved first, but I personally think that's a waste of money unless you race. The biggest thing that will help tire wear (other than what you've done) is proper tire pressures and the occassional tire rotation. Normally the LF takes the most abuse so swap it to the RF or RR if you don't have to dismount it. As I recall, my starting pressures when I used the Victoracers was around 30 psi...and adjust from there using a pyrometer (and seat of your pants).

[IndyDave]

Originally Posted by tigerdrvr

What pressure were you starting at?
The Kumhos should be able to live at -1.5 with no problems.

My tire pressures were in the mid 30's to start, and they went up to the low 40's.

I'm not surprised to hear what "wtknght1" said about how much negative camber the race guys are running.

As far as running the car on the street and at the track, that is true, however, I have a number of track events this summer and I am willing to limit my street time in order to keep an aggressive alignment.

Thanks for your input guys.

Subdriver - if you are online these days I'd be curious to hear your input.

Thanks again

[Subdriver]

Originally Posted by IndyDave

Subdriver - if you are online these days I'd be curious to hear your input.

Thanks again

I might be spending a few minutes here and there online.

Wtknght covered it well and I agree with him. I'll emphasize that it is okay to swap these tires side to side. I switch mine inside of car to outside of car every session to even the wear you are seeing (no dismount needed and ignore the rotation arrows on the outside of the GS-CS tires). Just take the wheel off and put it on the right side.

Keep a close eye on that edge of the tire. When you see cord, it is done. That is normally where I wear them out as well.

Your pressure is fine for the GS-CS. Having a pyrometer helps and they are fairly cheap. With a pyrometer you can check temp about 1" in from outside, center and 1" in from inside. If outside is hotest, add negative camber, if outside is coldest take out negative camber, if center is hotest, take out some air. It will be hard to make that work on the inside tires on a track that predominantly turns only one direction. That is why the left tires on a NASCAR have positive camber!

My gut feeling is that your pressure and camber are fine, just swap the tires from side to side to even wear and you'll be fine.