Excessive Rear tire wear?

Have a 99 C4 and running pirelli Pzero Rosso 285 30 18 in the rear. Bought them at the beginning of last spring and did wheel alignment and put on 15 000 km on them. Was stunned to see that they are almost down to the wear bars today. I did not expect that at all. I drive harder in my Mustang and get 50 000 km out of my tires on that car. Mix of highway and street driving. It is her car, and she drives normal. Doesn't punch it off the lights, doesn't push in corners etc ... the rare burst of spirited driving. I have searched online to see what the hell is up. Seeing that some say 10 000 miles on the low end and 20 000 miles on the high. I'd like to hear more about this out there. A set of rear tires every spring is not what I expected ...

Is the wear even all the way across or more toward inside or outside. pictures ?

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a little more worn in the middle. Had the camber straightened out by Porsche at the last alignment after I did my strut mounts. Too dark for pics right now, but they are not worn down on the insides.

Tire pressure.

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oh I know about tire pressure. But its not that much more worn the the rest of the tire. Overall the tires are worn down.

15k km very good for rosso...

What is the rear toe set at? Mine was eating tires too, largely on inside edge and middle. Added a tick of toe to the rear, and big improvement.

[QUOTE=jim010;16716952] It is her car, and she drives normal. Doesn't punch it off the lights, doesn't push in corners etc ... the rare burst of spirited driving. Who knows what she is doing when you are not around.....

Alignment. Do a title search and look for threads where suspect tire wear comes with users posting alignment settings. I have over 15,000 miles and my rears are still good (Michelin AS/3) on a 99c2 cab.

Rear engine cars is going to wear faster than a front engine...

Geezuz ... well this is what I was wondering. Do the Rosso's really not last very long. The fronts still look like new, though, with the car being a C4. Don't know. The Porsche dealer set it for us after buying the tires. Invoice doesn't say. I just trusted them to know what to do. They did straighten the camber, as I said earlier. Hah! You never know. The fronts look as good as the day we bought them, though. As I said earlier, Porsche did the alignment, as I had the front struts replaced at the same time. That was last spring. And yes, I have looked at many threads. Geezuz, no kidding ...who'd have thought that my wife driving her car like a Camry would wear tires 3 times faster than me in my Mustang ... It was a surprise to me. Maybe we'll go back to the ugly 17 inch rims as tires are cheaper for that size.

I have about 17,000 on my Michelin PS4S tires and the rears will likely need replacing in the next 4 or 5k miles. The fronts look great.

So that's 27 000 km! Rubber on those Michelins must be harder than the Rossos.

Dang! I run the Michelin Pilot Sports AS3's front and rear. I keep the tire pressures at the recommended psi for 18 inch wheels, 36 front and 42 rear. Over the years my tires do not wear much, so what I have to do is replace them because they age out...over 5 years. They begin to form small cracks around the sidewalls, probably from UV sunlight. I always detail them when washed and put some UV protectant on the tires. For someone who is wearing out tires, get the alignment checked and make darn sure they know what they are doing, with recorded printed before and after settings. The tire wear factor is also important. What is the tire wear figure for the Rosso's?

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Alignment isn�t something that is �set correctly,� it�s a series of adjustments with ranges that have pros and cons for those settings. So you could have 5 identical 911s with different alignment settings that all behave differently, handle differently, and have different tire wear, and all alignment settings could still be �correct.� Often, the factory recommendation for alignment will wear out the rear tires faster than a more conservative setting, so as the settings I have on my car.

220

Not sure what you are suggesting here. All I can do is have a shop do the alignment, which is what I did.

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220 The Michelin Pilot Sport A/S 3+ has a treadwear of 500 with a 45K warranty. That's a big difference. Like I said, I age out before I wear out.

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I just checked, Michelin Pilot Sport 4S tread wear rating is 300.

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Probably, when the 2002 2nd Gen 996 came out, in the door jamb where most PSI spec's are listed it had listed 36 PSI for the rear tires if there will be passengers in the rear seats. If there is nothing heavy in the rear seats & Psi is 36 in rear tires the middle band of the rear tire will wear very Fast.

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I don�t think you understand how alignment works. It�s like tires. You can just say to a mechanic, �please install tires,� and they might just do that, but they shouldn�t without consideration for application. Just like there are a dozen different types of tire ranges for climate, tires made for specialized purposes for wet versus dry, hot versus cold, handling, some that excel for braking. And a dozen brands and different wheel sizes with pros and cons of each. Different rubber compounds, some meant for tire life, some meant for lateral G force in turns. Same with alignment. Just �having it done� by a shop is like saying �a have new tires� without any consideration to what type, brand, season, application. You wouldn�t pick high heels to play basketball in, any more than getting your alignment done without telling the mechanic what type of alignment settings you prefer. Otherwise you could end up with an alignment setting that wears out or tires, or one where the handling isn�t very good. Does that make sense?

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Interesting. My 996 calls for 36F/44R.

I've owned a 2001 996 since new.....I reliably need new rear tires every 12,000 miles. 63,000 miles, alignment every time. I'd call it 'normal'.

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220 is a relatively "soft" tire. Your wear is probably about right for that tire. What did you say 15,000 Km? Depending on how worn they actually are. I haven't seen a photo yet -so I can't provide my "professional" diagnosis. One thing that I note, is that you have seen more wear at the center of the tread. This is consistent with over inflation. I'd suggest backing off at least one or two psi in the future. 300-400 is my "happy" spot for street tires. Still enough grip to be safe and enough wear resistance for 20k-30k miles. This assumes all else is in good condition (alignment and pressures). For track use, a lower treadwear rating is preferred. That's where 220 and lower are best. I have no tolerance for tires with large numbers for treadwear (generally 500 or above). There are some exceptions, but grip is usually sacrificed at the expense of tread-life. That's not a sacrifice I am willing to accept with my vehicles.

Scott, can I pm you?

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Of course you can.

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A lot depends on how you drive, worth it to monitor tread wear & adjust PSI for best wear across the whole tread surface.

I went through this too Jim. You’ll see old posts from me about it. As others have said, the first thing is to ignore the recommended 44 psi for the rear, it wears out the centres like crazy. 38 psi seems to be the sweet spot for me, maybe even 36. As far as alignment, again, I went down this road. The alignment shops machines all are built with a “range” where they are in the “green”. It’s actually a fairly wide range. If they are really paying attention, and few do...if green, good, never mind the number. Aa good friend is a automotive tech teacher and we just had this conversation the other night. Students rely on the technology of the machines, and don’t really understand what’s happening. He’s actually taken to forcing his students to learn to use strings, so they can actually see and understand what is happening, but I digress. My experiences is most shops, if they even look at the numbers, tend towards as close to zero toe as spec allows. On these cars, in my experience, this leads to excessive wear, particularly on the inside edge. Add a little extra toe (still within spec) and wear evened out for me at least. I was getting 10-12,000 kms on a pair of rear tires (wear rating 220-340) prior to learning these things. My last set (Michelin PSS - 300 rating), are past 14,000 kms and still going, even with 3 full days of track use.

Thanks. I am not replacing the rear Rossos. As sticky as those tires were, this car is not driven anywhere near where we need those extreme performance levels. Instead I am going with a suggestion by Scott and getting Continental Extreme Contact DWS06 all around. When they do the alignment, I'll talk to them about adding toe. As for pressure, yes, I'll drop it a bit and just keep an eye on it. The car alternates between 1 passenger and 4 passengers.. On trips it is 4 people with cargo.

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Toe, Front and rear?

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1999 C2 Cab alignment settings. I have 16,000 miles on the tires and the wear is even throughout all 4 tires, lots of life left, probably 1/2-way. Includes 2 days of tracking for about 300 total miles of tracking. The rest city and highway. This alignment setup is not the best for handling, but very good on tire wear, yet my car handles great to me.

someone will have to explain to me how going zero toe or as close to it as possible would lead to MORE tire wear. Zero toe is a tire that is dead straight. Any toe in or out would result in some scrub, which is actually what wears tires, not camber. For safety purposes, a little bit of toe in is needed in the rear, but the front you can run close to zero. The more positive toe (toe out) in the front, the more tramlining you'll get, but it will be ultra responsive. Toe out in the rear results in a very unpleasant experience with the rear stepping out all the time. Find the correct specs for your car, and ask them for a little bit of toe in and minimal negative camber.

I think basically it amounts to static and dynamic forces. When the car is static (not moving) the settings are for a car at rest. When the car is moving, dynamic forces apply...down force increases, the tires heat up, the whole suspension setup changes. You want some toe when it is set static, so when the car is moving and the dynamic forces take over, the car and suspension will move to a more neutral setting. Too little static toe in will result in too much toe out at speed. Make sense?

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I was talking about a 2002 C2 20 years ago,I may be wrong on the Psi. spec. Is your's a C4S ?

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No, I have a C2

New tires all around installed today. I put on the Continental Extreme Contact. Backs went from 285 down to 265. Alignment done. Showed the guy the alignment sheet and he did it to those specs. I'll report back in a year or 15 000km, whichever comes first. I hope these wear better.