Rear Tire Issues
 

Hello All,

I am having ongoing issue with my 2001 996. I live in San Antonio, Texas and drive my 996 approximately 3000 miles/year (almost all highway miles). In the 2.5 years of ownership, I have had four (4) REAR tire blow-outs. The original owner was running Michelin PS2 Cuos all-around. My first blow-out looked as though both inner- and outer-sidewall separated from the tread section, it occurred at highway speed (70 mph) and I did not hit or run over any debris and the tread depth was still reasonable in depth. The only warning I received was 2-3 "bumps" (like running over expansion strips) and then BANG - tire gone!

After this first blow-out I wanted to replace all the PS2 Cups with normal PS2s all around, but it was at the time when there was a nationwide back-order of that model in 996 sizes. There were very few tires available and in stock that were sized for my rear rims (i.e., 290 mm), so I settled for Bridgestone Pole Positions all around. Certainly not my first choice, but reasonable. I must mention that all my tire purchases were through DISCOUNT TIRE. Unfortunately, the shop near my home is the busiest DISCOUNT TIRE in the city. My subsequent blowouts were exactly the same as the first, tread separation from both sidewalls.

I have been talking to numerous individuals, including former employees of .DISCOUNT TIRE and they have told me that DISCOUNT TIRE is all about speed and volume - they no longer carefully clean the bead area on the rim, nor do they perform a high speed rotational balancing on the tire/rim. This kind of service might be OK on "normal tires", but not on a 290 mm/30 series expensive, high speed tire on a Porsche Turbo. If this is what DISCOUNT TIRE is actually doing, it is knowingly negligent on their part, as any upper level employee of a large tire store must have, at least, a basic knowledge of the physics involved in the rotation of this type of tire and the stresses an imbalance places on the sidewalls and tire, in general. My last blow-out occurred yesterday going 60 mph on a smooth, straight section of road with no debris being present.

I apologize for my long-winded post, but I really appreciate you letting me vent. This is becoming insane and VERY expensive.

I would really appreciate any input of ideas.as to what is causing this issue. Both wheel wells have been examined for any protrusions are problems that would rub or hit the tire.

Thank you in advance.

Wow - what a mess. Did Discount Tire do the install on all 4 of the blowouts? Is it always on the same side? If so, I'd suspect that maybe the wheel is the problem. I've used Discount Tire before with no issues...but I "interview" the shop manager and make sure they have experience mounting specialty tires and use road force balancing equipment and then I watch as they do the work. So the problem could be:

tires - seems unlikely you got 4 defective tires - hope you're buying the protection certificates at least after the first blowout.
mounting - maybe - ask for their most experienced tech to do your mounting and watch
wheels - are the wheels being road force balanced

Good luck

Thanks for the reply. Sorry for the delay in responding, an insane day at work.
Discount Tire mounted all the blow-out tires, except the original Cups, which came with the car from the original CA owner. . I asked for their most experienced mechanic, but the shop is like a proverbial "Chinese Fire Drill" with multiple Techs working on each car (and loosing expensive valve stem caps, etc.). I believe from talking to various individuals;ls that they do not use Road Force Balancing.- the time required would cut into their profit.

saw, have you taken your car to an alignment specialist at any point during this saga? It sounds to me like you have excessive wear on the inside of your tire. I went through a similar blowout fest on a B6 Audi S4, years back. It turned out my aggressive negative camber (stance nation, yo) ((not really)) was making the car eat the inside of its tires, but in two instances I had a blow out on both sides.

Shame about your Discount store. I am a big fan and promoter of my local store. You have to pay for the road-force balancing, but they really should ask you if you if you'd like it. If I remember correctly it's something like $20/corner at their stores. Is there another location you could give a shot? They are unfortunately not all one and the same... but there was a love-fest thread on here a while ago for the store and it sounded like most DT stores are pretty decent across the country.

FYI - I'm also running Pole Position S-04's. About 6,000 miles in and I'm at 8/32 front, 6/32 rear.

Thanks for the reply. Although it has happened on different rear wheels and sides of car, I too am suspecting my rear geometry. Although, I would think that I would see uneven wear or have handling or vibration issues. But I too am not a Tech. I'm been trying to find a good alignment shop, as I heard the Porsche dealer does not do very good work and most individuals use independent shops.

Dr. S -- Thank you! I have never even been asked or told about Road Force Balancing at Discount Tire. I just assumed that on high-priced tires and installs on sports cars, they would mount the tires in a correct and SAFE manner. I always get involved when my sports cars are being worked on. However, at D/T when I try to get back into the shop, they cite Insurance Regulations prevent this I watch from just inside the garage door but you really can't see what is being done. This latest blow out also caused damage to my fender flair area from the layer of tire material flapping - I had to get off the highway as I was on an insane section of I-35 with no break down lane and absolute maniacs driving at 90 mph in a 60 mph zone. And I thought MA and NY drivers were crazy...... .

Sorry for my screwed up replys. I have to learn the new Repay system. This is a great, highly advanced reply system they are using. Good for Rennlist!

My recommendation would be to get a new set of tires and take it to a porsche dealer and have them do an alignment. I dont think this is a tire problem, I think it is a car problem. So if theres some car trouble that wont allow a alignment to spec they will know what it is.

I think you tire problem is from low tire pressure. Every tire I have seen that blew out on a Porsche (and I have seen hundreds) were either from wearing out on the inside to the cords and beyond( unknown to the driver because he can't see the inside very well) or from a nail puncture that causes a small leak and over time ( sometimes weeks or could be overnight) the pressure will get low to about 15-20 psi and not even be noticeable looking at the tire, it will still be standing up good. The sign that a tire has ran low on air is a pile of rubber "dust" inside the tire when removed. I mean like a handfull of rubber dust. If the tire hits someting in the road or just "explodes" there will be bits of rubber , but not "dust".This is also the reason ALL cars after 2007 now have TPMS ., its a LAW. Porsche cars are the worst at picking up nails as the front tires are sticky and pick up the nail and flip it, and a lot of times it flips just right to land pointing at the rear tire !!!

FWIW, the rear camber on these cars trashes the inside tread on the tires in a fairly short time........

you can if you choose to, set the camber to neutral and vastly extend the tire wear.

I have 150k on my 2000 C4 and changed the camber to neutral after eating two sets of tires in 25k miles. I am not an aggressive driver, love the car and am very happy with its performance and ride.

I agree, I did the same thing on my 99 996 Coupe, set the front and rear camber to 0 to save on tires and money. Can always set back to aggressive camber for track days when necessary.

Try checking your pressures every morning before you leave for the day. I do this and have found slow leaks that would eventually have caused a blowout. Even found a crack in one of my rears on my C2. Have you ever had your valve stems replaced? They could be 17yrs old.