DrJupeman

Car: '94 Turbo 3.6
Wheels: 10" 993TT Hollow Spokes (narrow body offset)
Tires: 295/30/18 MPSCs
Tire pressures: 34 psi hot
Camber: -2.7 degrees

At Lime Rock today the sidewalls on my Michelin Pilot Sport Cups "failed". They developed severe waves in them as if the sidewall carcass had broken. The tires had ~ 5 runs on them. I am very diligent with tire pressures. The tire wear on the tread is very even. I have not taken tire temps but my trusted mechanic, who has raced a similar setup, is very confident that my current alignment settings produce even tire temps across the tire. The wear indication matches this claim. What can be causing this type of very premature failure? What do I do to fix the problem?

I have also had 285/30/18 MPSCs fail this way (maybe after ~5 days) and a set of Dunlop Super Sport races.

Help, my car is chewing through tires and I can't afford 5 runs per $300+ tire!

vegasgolf98

Run with a chicane . . ok . . .you KNOW somebody was going to say it . .

DrJupeman

Alan C.

I've had this happen before. In my case the bead was damaged when the tires were mounted. I was told this caused the problem. Somehow air got in between the plys. Not sure if that is 100% correct or not but it seemed possible.

DJF1

LOL...I hope the Michelin problem did not migrate on the MPSC's too! Seriously that is very odd. I have gone through several sets of MPSC's and each has lasted an incredible amount of time. Your can weight is very similar to mine, the rear negative is identical to mine and the 34-35 Hot is what I get starting some times ast 25-26 cold. Your mechanic is right, with these settings i also had very even tire wear and the temperatures max range difference is never more than 14 degrees farenheight which shows very even temps accross the tire. I suggest you contact Michelin Motorsports and save the tire to send it to them. Hopefully they will come through and replace it for you. Hopefully you did not have an accident? Please let us know what you find out and good luck!

lwilkins

I had much the same experience on the rears with Hoosier S04's , and to a lesser extent MPSCs, but I blamed my limited slip that was failing and allowed inside rear tire to spin. My first racing weekend, I came in for my pit stop at the 1 hour mark and had 1 inch of cord on the inside rear tire. My mechanic blamed Hoosiers, so I switched to MPSC's but haven't had enough track time since then to form an opinion whether Hoosiers were to blame.

But the inside of the MPSCs exhibited similar overwear, so I swapped sides to even it out. Temps showed hotter inside on both rears.

That could be either a worn out limited slip, or too much negative camber. There was a bunch of inside tire spin on acceleration, especially in slow corners. I've got a new limited slip differential on order, and am thinking that will solve all problems of this sort.

I was running 3.0 degrees camber, and planning to take it down to -2.5 degrees. I've been running hot pressures of 38, any idea if that is too high?

DJF1

What are you driving??? For the 993 Michelin recommends 32-35 Hot.

DrJupeman

Thanks for the comments. I believe my limited slip is working as I do not get tire spin. Further the tires that have failed have been the left rears which are the most loaded, particularly at Lime Rock (which only has one left turn). As such I was suspecting it is more a case of the tire having to deal with the fat car, high loads, and a reasonable amount of torque (Turbo 3.6's are rated at 384 ft/lbs).

Anyone have contact info for Michelin Motorsports?

Oh, and I did not have an accident in any of my failures this season. I have gone into the wall at 120 mph when a Pirelli slick delaminated on me in my GT3 Cup, however! Seriously, I was a bit lucky with the previous MPSC failure as it really let go in a spot where I had room and no one was near me. This time I was a bit lucky as it began to fail when Food Angel was driving and am happy nothing happened then.

Alan G.

Charlie,

Nice to meet you and the Angel. It might be a longshot, but try to get the tire to Michelin Motorsports at LRP next weekend. With ALMS in town you should be able to get some feedback from the pros.

Either call your Michelin dealer for corporate contact info, or search the web to have a corporate referal for your tire. My guess is that they are looking for any good PR that they can get.

Alan

DrJupeman

Thanks, Alan. I sent Michelin Motorsports a note off their website. We'll see if that works. This tire was purchased through TireRack so I will call them to see if they can help.

There is a small chance I will make it back to LRP for the ALMS next weekend. If I do get there I will bring the tire...

Because I also ruined a Dunlop Super Sport Race in the same manner earlier this year I suspect it is not a tire issue, per se, but no doubt something with my setup. What is frustrating is that the setup looks perfect in every way other than the failing tires! Oh, and driving slower is not an option...

tlark

Please do keep up posted on the issue and Tire Racks response. I havn't ordered yet but the MPCS and Corsas are my options. Leaning to the cups b/c they wear better but this is a concern.

James Achard

-3 deg camber is way too much for these tires. I was running -2.5 on my car and was still seeing a 30 deg difference inner/outer. Removing some of the camber solved the problem. Tire temps do not lie. Every car is set up differently so using a generic number for camber can lead to problems.

Be very leary of what tire rack tells you. 911's are a unique animal in regard to tire setup.

Cheers, James

DrJupeman

I was at -2.7. What do you think I should try, -2.25?

ldw

This is extremely unusual for both the MPSC and the Dunlop SSR.
I have put well over 6-7 hrs of time on a set x several sets each in a 3150 lb GT3 with no problems and no sign of unusual or uneven wear. Most of the track time was a combination of LRP and Summit Point. Since the culprit corner is the driver rear and most loaded, although mounting and bead damage may be an issue, doubt it. I suspect that given the torque of this car in combination with the wheels you are using, you are getting significant tire rotation on the rim which is building up heat and damaging the sidewall. You can confirm this by simply marking the tire at a point on the rim-say at the valve stem inlet.

Such rotation is very common on all tires and cars pushed hard at the track (commonly is seen on race cars with slicks too), but I am suspicious that it may be very severe in your case. Different 18 inch wheels have different tolerances. Perhaps a different set of rear rims and slightly higher rear pressures will solve the issue.

If you have even wear and an appropriate spread of temps, then your camber is appropriate. You are in the range of the recommended tire camber and on a GT3 platform, I use significantly more than 2.7 in the driver rear at LRP and Summit point. As James says, each car is different and the driving style and skill is also a huge factor. So, use the wear and temps as your guide.

DrJupeman

Sounds like good advice, Lynn. For what it is worth, the failure on the DSSRs and the MPSCs happened on different wheels (DSSRs, Speedlines, MPSCs, 993TT Hollow Spokes). Nonetheless I will mark the wheels/tires to see if I'm rotating them.

Some more data points: I have run MPSCs on other cars with no issues. I also ran them on this car with the stock suspension and did not have this issue at all (I just wore them out prematurely on the outside). I suspect slightly less camber may be in store for the rear (fwiw, I'm running -3.2 in the front and the wear there seems great).

I will buy a pyrometer and likely change my camber to see if I can start to trace this problem. I need to cure it before the Mosport club race at the end of July!