Pirelli P Zero Tire Blowout Need Advice

Hello All, I'm a new member to this discussion board and have had my 996 for three months now. This past weekend my right rear Pirelli P Zero blew out at 110mph on I80 going to Lake Tahoe. The inside sidewall (engine side) just disintegrated. I'd say the tire was about half way through it's life and still had decent tread life left. I was shocked to see the condition of the tire when I pulled it off and put on my small spare. When placing the tire and wheel in the front bonnet, what looked like small pieces of burnt rubber fell out from the interior of the tire. Since I've had the 996, I've smelled an unusual smell from the engine area and could not figure out what it was. There were no engine leaks of any sort that could account for the smell of something hot or burning. Can the exhaust get that hot that it will affect the tire? Or was my tire possbile rubbing on some part of the supsension that could cause it to wear out on the inside sidewall? When I purschased the p-car, I replaced the 17 inch rims with 18 turbo twist rims. The tire size of the blown out Pirelli is 265/35/18. Tire pressure at the rear was 44psi cold. I have just ordered two replacement Pirelli P Zeros for the rear and should get them by week end. I don't want the same blow out experience again. When I bring the car in to have the tires mounted (I hope my rim wasn't damaged) I will look for any signs of rubbing in the inside tire well. Any possible advice or suggestions? Thanks in advance. 99 Black 996 Coupe

[quote]Originally posted by nocaguy1: <strong>Since I've had the 996, I've smelled an unusual smell from the engine area and could not figure out what it was. There were no engine leaks of any sort that could account for the smell of something hot or burning. Can the exhaust get that hot that it will affect the tire? Or was my tire possbile rubbing on some part of the supsension that could cause it to wear out on the inside sidewall?</strong><hr></blockquote> (1) Didn't notice any leaks, etc. in PPI (2) Tire life had plenty of tread when inspected at time of purchase. (3) Experienced strange smell from engine area ("burning rubber" perhaps?) (4) Tire burst at high speed. Signs sure seem to point to the fact that the tire was rubbing against the wheel well, and the friction generated at high speeds caused it to burst. 996's can obviously easily take 18"-ers. Likely cause is that the tires weren't mounted right when you upsized. Would love to hear what the dealer/my compadres think. Regards.

Did it look like this? This is a 295/30ZR18 Pirelli Asimmetrico off the Turbo. Firstly, the most common cause of a blowout is a low pressure condition. Either the pressure isn't checked for a long time (these tyres loose air through the rubber very quickly because of the high pressures) or else there is a problem with the valve or even more likely, the tyre gets some sort of slow leak from a nail or something. Inspect the tyre very carefully to see if this is the case. No, it is extremely unlikely that the heat causing this blowout came from the exhaust or externally. The heat causing a blowout is generated deep in the tyre around the plys that hold the tyre together. The problem is that the heat here cannot escape easily. This is why the pressures on these tyres are so high -- to minimise flexing and therefore minimise heat build-up. The reason for the smell and bits falling out is that you opened up the tyre to the point that is hottest and can literally smell the burning rubber. It was very much the same on my tyre. If you look on the ground you can see a trail of tyre bits in this photo: The tyre fails at the inside edge because this is the point that gets the hottest. Remember, the Porsche runs the rear tyres with negative camber. So when you are going straight down the road the tyre is basically running only on that inside edge. That's why they wear out first there. The loads are higher on the right-rear tyre in straight and level driving. It will wear about 1 mm more over its life than will the left-rear. So let's say that you find no nail and no other cause for the blowout. Then in all likelihood, the cause is a defective tyre. We already know that these tyres are shifting their belts and going egg shaped (I have a couple like that now and every single Asimmetrico has given me trouble in one way or another). In my own case, the blowout happened at 200 km/h after I slowed from cruising at 230 km/h because I started to feel a vibration. The tyre pressure was being carefully watched and no signs of a puncture. Clear signs that the tyre was defective. On the good side, with the width of the tyre a blowout was no big deal at all. But I hate to have thought what would have happened had it been twisty mountain road instead of highway (a half hour earlier I had been going very fast on a mountain pass). I grow to really not like the Pirelli Asimmetrico (the Asimmetrico is 1990's technology -- we're not talking about the Rosso which is a different tyre entirely). Please post some photos if you can. S.

MAYBE THIS WILL HELP FWING'S REPLY.. I GUESS IT'S EVIDENT THAT THE TYRES ARE WORN MORE ON ONE SIDE.. WAZ 996 C2 99

I had a blowout on my left rear tire too, soon after I bought the car. This was on 285/35/18 S-02. That tire was immediately discarded but I found that the right rear also had just one patch along the inside edge that was particularly worn. Took it to Custom Alignment in mountain view and they said the same thing FixedWing said, that the tire must have been underinflated and running hot. Subsequently it suffered damage from impact on road irregularities and the tread started separating. Fortunately it blew up on the 101, half an exit away from Rector Porsche. Unfortunately it broke my wheel. Hard way to learn the importance of keeping tire pressures right.

Hmm. I had Contis on my 00 Cab that lasted the distance. I replaced them with Pzeros and had two flats in 4K miles (both rears). I bought a 02 Cab (came with pzeros) and have 3K miles on it. I got it out of storage today, flat tire. I called my tire guy (who knows me on a first name basis now) and he, without me telling him, said "right rear"? He told me he replaces right rears on 996s all the time... This week, one Pzero, set for my truck, and set for my wifes Lexus (they only last 11K miles too...). Roy

Thanks everyone for your replies. I will be checking tire pressure contantly. Fixedwing, my blown out tire looks exactly like yours did, all around the tire, including the burnt rubber shreds. 99 Black 996 Coupe

I would suggest the Smatire system, gives you a nice peace of mind. <img src="graemlins/burnout.gif" border="0" alt="[burnout]" />

had a blowout on the a rear Pirellis Asymmetrico 4 months ago on the 280......got lazy with the tire pressure. Seems to be the penalty. Replacing the tires withe new Pzeros does not seem to solve the problem of pressure loss. Tires handle great but a week in the garage = 1-2 pounds of pressure loss. Never had much pressure loss on the Continentals that came with the car (they were trash though) or on my Michellin Pilots on my Dinan BMW...... Can't wait for a better tire with the same performance....Any suggestions? for now....buy a very very good tire pressure gauge. Audi has some pretty good ones.

Low profile ultra-high performance tires are prone to this type of failure nowadays. If these tires are allowed to deflate significantly on the car, running or not, unmounted you can see the very slight damage to the area where the sidewall and tread join in the form of small pores in the membrane inside the rubber. All it takes. Air migration into the rubber is the cause of the blowout at some (unpredictable) later point once this damage occurs, even though the tire may never be run overly hot due to underinflation. I do not doubt that hitting potholes and such hard enough could cause the same type of defect. This is not to correct FixedWing's post, which is quite right so far as I know, just pointing out there is another significant cause for sidewall failures in properly inflated tires. BTW tires going out of round and recovering their shape as they roll under load is called hysteresis, which causes friction, which is reduced by shrinking the contact patch and thus deformation as inflation increases. If you drive fast, I would add this to your thinking, and quite possibly have any tire that is losing more than a pound or two per month unmounted and inspected.

[quote]Originally posted by NMoore: <strong> If these tires are allowed to deflate significantly on the car, running or not, unmounted you can see the very slight damage to the area where the sidewall and tread join in the form of small pores in the membrane inside the rubber. All it takes. Air migration into the rubber is the cause of the blowout at some (unpredictable) later point once this damage occurs, even though the tire may never be run overly hot due to underinflation. I do not doubt that hitting potholes and such hard enough could cause the same type of defect. </strong><hr></blockquote> Nick, I really cannot be sure what the cause of my own tyre failure was. Alas, I didn't get to see the tyre again when it had been removed from the rim. Now I really wish I had. I really don't believe that in my own case it was a low pressure condition. We were on holiday in difficult conditions (the blowout took place in Turkey and we had just driven down through Eastern Europe). We were covering many miles each day and I was keeping a close eye on the tyres to avoid problems. Notably, I had not had that tyre since new. It came mounted on an extra set of wheels I bought. And when I felt inside of the tyre I could see that it had had a small nail in it and had been successfully patched (this nail hole was not the cause of the blowout). So it is quite possible that the tyre had been flat at some time in its life. Whether this was the cause I don't know. I've had just about every Asimmetrico deform in some way. The current two on my car are egg shapped. But this is the only one that had blown. And I am regularly doing some very high speed cruising. Anyway, my original advice is still good. Check your tyre pressures very regularly. With the hard sidewalls it is impossible to see and usually to feel a low pressure situation. And for high speed highway driving the pressures are critical. Unnoticed small nails in tyres and neglected tyres are still by far the major cause of blowouts. Oh, my experience is that these tyres will loose about 0.1 bar of pressure a month (on the Turbo, the rears are meant to be 3.0 bar and the fronts 2.5 bar) so a little over 1 PSI per month. If the loss is four times this then I would agree that this needs to be investigated. S.

FixedWing--I was not trying to correct your advice on pressure at all, agree 100%. The reason I know the factoid on air migration is that I had a nail through one of my original egg-shaped Contis (had THAT too), which I noticed right away and only deflated partially. I looked inside the tire at the shop, and although the nail hole through the tread was slight and clean, the partial deflation of the sidewall had failed that inner membrane there slightly, not near where the nail was. Look inside any high performance tire, the innermost material is not rubber. I believe that is what failed your tire, it had most likely deflated under load when it had that nail resulting in the same defect, which is a time bomb. Exactly what they warned me about at the tire shop. Notice from the pics you did not have a tread separation, which is the tread coming off the belts which is almost always from running underinflated and hot, just as you advise. That is a blown sidewall. My point is that anyone who has had a tire significantly underinflated for one single moment should get it unmounted and inspected, about $25. FWIW a rule of thumb is 1psi per month, 1psi up or down for every 10F change in ambient temperature.

[quote]Originally posted by NMoore: <strong>FixedWing--I was not trying to correct your advice on pressure at all, agree 100%. </strong><hr></blockquote> Don't worry Nick, I didn't think you were. In fact, I am always happy to hear what people have to say. That's how I learn. Speaking of which, can you explain exactly what "air migration into the rubber" means? What I'm curious about is how this might damage the tyre. We know already that air will slowly pass through the rubber. I can think of a couple possibilities. 1) the air bubbles produce localised hot-spots inside the tyre. 2) they allow the belts to somehow move and seperate locally. But these are just guesses. Have I missed something? Is there any way to repair this damage? I would think that this could even happen from mounting the tyre as the tyre can get pulled about quite a bit in the process. S.

I think your hypothesis is a good one. Anyway, it would seem the interaction between hot, high pressure air and the rubber is something the tire engineers are trying to avoid. I cannot guess why the material so fragile at the junction of the tread and sidewall. By the way, I am happy to see that only your tire got hurt when that tire went. I once had the wheel and 18" S02 come completely off a 300ZX-TT due to the wheels being over-torqued. I was driving to the shop to find out what the noise was! I was only going about 10-15mph and braking when it went, and that tire and wheel went about 400 yards (without incident).

I don't know that I can contradict all of the good info on air loss over time. I think there may be one more factor with the factory recommended rear air pressures and hard driving. On a single track visit with my 02TTX50, I noted rear tire air pressure rise over 56psi (58 psi by my recollection-I may have indicated it precisely in an earlier post) in just 5 hot laps. This was starting with confirmed factory recommended rear air pressures. I wonder if your blow out wasn't related to super high air pressures after prolonged hard driving. My Pirellis were ruined by the 5 laps and were replacd by the dealer at no cost due to apparant belt shift resulting in uncorrectable tire vibration. From this point on, I'd be concerned about the Pirellis for any sustained high speed driving. I think you've got to check the hot pressures and bleed the tires when heat results in a significant rise. AS

It must be well worth checking with the manufacturers about maximum hot pressures, track and street are really not at all the same environments. Argues for a shaved set too, less heat, although you must generally only have brand new tires shaved.