JET951

Here we go, a falken slick, only a few laps old.

J richard

Yup that's weird looking!...

I think the way to tell if it's an internal failure the failed areas diameter would be bigger than a new tire, if it's worn, smaller...time for a string...

wanna911

Update. The higher tire pressures did help alleviate the inside edge cording, as well as relinquishing any grip the rear tires had

Outside edge of tire corded similar to last time, pretty certain something is cutting it as the tire temps were in the 160's to 170's on the inside edge, so very safe.

I give up on full slicks, too much hassle for me and as of yet I haven't gotten any speed benefit from them. I'm not racing either, so no real need for them.

85Gold

We had the same problem on the GT2 @ the UTCC in 09 with the same sizes you were running. Rear inside corded with 4 TT sessions. We were running 30 psi hot (Hoosier recommendation) and tire temps were 180 inside to 160 outside. Jeff from Hoosier was there and did not have an answer. -2.5 rear camber and .15 toe in each side. Fronts were fine. Haven't tried them since.

Peter

wanna911

Peter, was it the driver side rear?


I think I've come up with an answer as to why I'm only having this problem from the left rear tire. I think the car is suffering bumpsteer under load and the toe is changing causing that side to wear prematurely. Considering all of the tracks I visit (CMP, Barber,Road Atlanta) are all heavy right hand turn tracks (with heavy compression as well), it explains the difference. Also considering the car is heavy (3400 lbs with driver), has a big wing on it, and is powerful (600hp), it makes sense that the tires wouldn't last long. The passenger side rear looks like it could go on with no problem for a long time. That is the only reasonable explanation.


I have tie rod ends on my adjustable toe arms, now to see if I can get the bumpsteer adjusted so I can run some slicks!!!!

mos996tt

Had the same issue with my turbo. Car was way too heavy and not stiff enough for how aggressively I was driving it, esp with R6's. (-3 in front and -2.2 rear). Most trouble with that kind of wear was at WGI with fast left sweeper. Because of the stick, car was leaning and lifting the rear, thus scrubbing the inside edge of left rear tire. On r compounds, wear was much better - my only guess is that they don't stick as well so the car is drifting as it gets closer to limit, the left rear doesn't lift as much and rear tire patch has more full contact with pavement. Not an issue now since I got rid of the turbo and in a Cayman! (will save a fortune on gas too...) I was running 36-38 psi all around. Not certain that this is the explanation but when I went through the inside edge after a day and a half, I was pissed! I am guessing powering out of turns too early probably doesn't help tire wear either.

wanna911

I'm running -3.2 front and -2.6 rear and I get pretty decent wear on DOT Tires. There is still some taper on the inside 1/5th of the tire. But I've got 2 full weekends on a set of Kumho V710's and they still have life left in them. It's just the slicks that give me all the problems I'm assuming because of softer sidewalls.

I know it's the bumpsteer, now I just gotta find out how to get rid of it. My spring rates are good, my tire temps are good on the pyrometer, barely in the optimal temp zone (180's) and my driving has mostly been easy on tires. I know the outside edge cording was just the weight of the car and the height of the tire at Barber with the high loads due to the compression. I'm not concerned about that.

But if I can get rid of this issue, I'd be golden. The good thing is that I can test it on a set of DOT's and if the inside portion doesn't taper, I'll know I'm good to go back to slicks.

bobt993

What spring rates are you running?

Viperbob1

I gave up on the Hoosier slicks with my customers. Internal belt breaks, wires coming from sidewall (several times), and NO WAY TO KEEP THEM FROM WEARING LIKE CRAP. Did all these things in detriment to the customers racing efforts. Switched to Yokos (I loved these in the past). They have worked great. Same car same suspension setups (even more radical on one) and the things wear straight across and have great grip. Larger variety of compounds too.... We wind up throwing them out from heat cycling (12-14) before they wear out. And we use the 01/02 compounds typically.

wanna911

Are you using them on Tom's car?

What's funny is that I know guys that are running the Hoosiers with no problems on NA 996's with no problems. Very frustrating to see and not be able to duplicate. And their cars are run very low.


I've run 600 and 900 front with 1100 rear.

Viperbob1

Yes we use the Yokos on Tom's car now running -3.9F/-3.7R. They wear great. I dont know if it was the power, but we also had numerous tire failures on the Hoosiers. On a 997S that we race, almost the same thing. Now with a switch to Yokos, much better.

wanna911

What sizes are you running on Tom's car?

wanna911

Figured I'd post an update on this since it seems others have had similar problems. Between the Barber event with all the problems, we lowered the car even more (LOL) I ordered the Bumpsteer Toe Kit from Tarett. After much debate and some hours of talking with Tarett, we did a bumpsteer test to see whether raising the mounting point up or down caused more bumpsteer. Raising it up made it horrible. So we ended up making a HUGE spacer (probably about an inch) to lower mounting point.

The control arms were then completely parallel. After a weekend at the track, I can honestly say that there is no longer any hint of problems with the tires. I now feel safe going back to slicks again. This is a must do for heavier 996's that are lowered. I just bought outer tie rods from Tarett as I already had adjustable Toe Links. The Tarett Bump kit screws right on there.

Car was over 1 sec. faster too (of course it was over 100 lbs lighter and had less wing angle and a gurney flap too).

mark kibort

this kind of wear is not bumpsteer. usually the inside tire is barely touching , as it droops, but it can scrub as you go around sweepers, llke turn 8 at willow. generally, it is not taking any abuse. the loaded tire, as you compress, toes out, and gets more camber (dramatically), but all that does, since its steering the car, is desensitize your steering. if the track has lots of sweepers bumpsteer could be an issue, but this doesnt look like it at all. and again, bump steer issues, act on that drooping tire and it usually scrubs out the inner 1/3rd of the tire, not the edge. on a street car with a soft suspension, this can be an issue, but not with a properly sprung track car.

You said you raised the car and the bumpsteer was aweful? obviously, you want the control arms to be as parallel as possible, as as you go lower, the movement of the suspension, creates a more radical change in camber and toe. raising the car, above parallel components makes it worse, due to starting out in the accentuated opposite condition, and then doing through the neutral point and down into the compression range.

your 1 second lap time woud normally be due to the 100lbs of weight, and the new tires you are running. Dont think the less wing vs adding a gurney flap would do anything. As we have talked about at great length, the gurney flap, on a given wing, will only equal the wing natural downforce at its max angle, by having it set 7 degress less of an angle. (albeit at 40% more drag if you are using a 5% GF, and thats around .5" for your wing).

going back to those tire pictrues, that is some serious deformaty. most of that is due to tire pressure or some internal falure of the tire's structure for the application car might be too heavy for this tire type.

wanna911

I wasn't running new tires. I'm still running the same Kumho V710's I put on last year after my slicks corded two weekends in a row, they have over 20 HC on them now, albeit a few of them short ones (~5 laps ).

I mean the inside edge of the loaded tire was giving problems, Road Atlanta and Barber both are almost exclusively right handers (heavy loading with elevation on top of that). The drivers rear was taking all of the load which is why the passenger side NEVER had any problems. More load + bumpsteer = toe out = inner tire wear right?