Re: Rear tire wear

It's about time to replace the rear tires on my 987. They are 235/50/17 Michelin Pilot PS2's.

I notice there is more wear toward the outside of the tire than on the inside. i.e. as one looks across the surface of the tire, the remaining tread gradually diminishes to where there is about 1 mm more tread left along the outside than the inside.

I had thought that the last time I replaced the rears, the tread had worn down more towards the inside.

Which treadwear pattern is normal?

If mine is unusual, perhaps a new alignment should be done (MikenOH had suggested on in relation to my vibration issue- which hasn't been completely cured by the new 4 wheel RF balance).

Is there a camber adjustment on the rear of the 987 (non-S)?

Or maybe this wear pattern is indicative of some suspension components wearing out?

see: [www.procarcare.com]


Thanks

Roger:
All of the rear tires I had on our 987 had more wear on the inside tread --maybe 1/32 more over 10K miles--than the outside. Our alignments were pretty aggressive relative factory settings(-1.8 to -2.0 rear camber vs. factory -1.5), so we expected more wear on the inside.

If you have excessive toe-in on the rears, I would think your outsides would wear more.
Given the cost of a set of PS2 tires, I think an alignment would be money well spent.

Agree with Mike. You need a good alignment by a shop that knows these cars well. Don't bother with Sears or some other chain. Typical tire wear for these cars is inside first.

Is it more worn on the outside edge (atypical, comes from very hard cornering) or on the inside edge (typical, comes from negative camber built in at factory)?

So, for clarity, inside edge wear is more typical of road-driven cars.

There is a balance between camber and toe in the rear.
As i recall, there is not much that can be done to explicitly change camber without affecting toe. the only adjustment i can recall is the toe link length.

So i would surmise you have either a shifted eccentric nut or worn components. It matters little, a good alignment will find and diagnose or fix this.

Most 987s dont yet have enough miles to have major component wear.....

Grant

Grant

gee-lenahan-at-gee-mail-dot-com

You're right, Grant; I contradicted myself.

I'll try again - The rear tires have worn more on the outside edge. The inside tread is currently about 1mm deeper (slightly above the wear bars). The outside edge has worn down to the wear bars..

The car has occasionally had some vigorous cornering, but not often nor long enough to account for what appears to be unusual treadwear.

The Porsche dealer arranged the last alignment. I say 'arranged' because the dealership is small - they don't have their own rack. I think they use the one next door at the Volvo, Jag, shop (they all have the same owner).

I agree - time for a new alignment.

Thanks guys.

R

Typically hard cornering does not result in an even taper from outside edge to inside, but rather destruction of the outside edge for about 1 inch.

And, its more in the front than the rear.

So i think you have a problem - alignment, worn part, or cosmic inversion.

Let us know what you find!

Grant

Grant

gee-lenahan-at-gee-mail-dot-com

You're right, Grant.

In the case of my tires, the decrease in the amount of tread is very gradual across the tire, and the right and left tires have the same wear pattern. The car has about 55k miles or so, many of which are on the open road.

The wear differential is not extreme - as best as I can recall, the last time I replaced the tires, the wear differential was greater, but the other way around - worn on the inside, not as much on the outside. The current wear pattern strikes me as odd.

I hope to get it in for an alignment next week. It will be interesting to see how it reads when they set it up on the rack. I'll let you know.

BTW, I'm still on the Blue Ridge Parkway, and having a terrific time. Sure do miss all the Porsches though.

Mine wear inside on the street tires and pretty much flat on the track tires. If it has been a couple of years, have it done. I have mine at the shop today.

FYI - Dealer did not balk at doing non-factory settings after camber plate installation.

Edited 1 time(s). Last edit at 06/03/2013 01:14PM by Laz. (view changes)

Yup, correct size.

Rears 235/50/17

Fronts 205/55/17.

Believe it or not, I actually wanted the 17" wheels (rather than 18"), as extra sidewall height helps with the bad local roads.

Now, 19" is the norm, and 20" is not at all uncommon.

Inside edge wear is the result of incorrect alignment. Based on the number of alignments I've had done to my cars and the before and after numbers toe is the culprit.

One of these days when I have the time I need to scan in some of these so I can post and show the numbers.

Outside edge tire wear while I can't recall ever having this occur on the rear tires has occurred on the front tires once on my 06 GTO (lousy chain tire store alignment) and my 996. In the case of the 996 the wear was not severe but it was noticeable. The cause was incorrect toe. The result of bumping the front tires against a low curb/sidewalk when pulling into a dark hotel parking late one night way past my bedtime.

The uneven wear took thousands of miles to manifest itself but the howling that the tires emitted took under 1K miles to appear. OH I remember now I didn't drive the car but maybe 3K miles until I had the alignment touched up. I could not stand the noise. The noise subsided and tire life was not much affected by the front tires still wore more on the outside edges than any other areas and they have before and since always worn evenly. Part of the reason was the tech told me with the tires already worn down and unevenly the alignment outcome might not be as good as it would be with new tires. I accepted this because I was willing to risk it to gain some quiet. Afterwards the car felt a bit strange, but not intolerably so and after awhile as the tires worn in a bit from the alignment the noise subsided and the car felt ok.

In the case of the GTO I do not recall any noise and I do not recall how soon I noticed the wear but since the fronts were due to be replaced along with the rears next time the rears needed doing I just ignored the wear.

Anyhow, these cars have a range of alignment settings that are acceptable. Different dealers (ignoring the one indy I've relied upon) have different philosophies. In one case one tech aligned my car and when I got the car back it felt a bit weird. When I took it back he told me he had aligned it that way to ease tire wear on my long trips/drives. I thanked him but asked him to give the car a standard out of the box vanilla alignment. He redid it and the car felt better. Tire life has always been acceptable with a proper alignment so I saw no need to compromise on car feel for the sake of a few more miles of tire life.

At other dealers the alignment is more aggressive to give the car I guess a tighter feel. But this can have the toe set in quite a bit and this can lead to shorter tire life, with the inner edges going in some cases in under 10K miles.

Always my advice is to get the car aligned by a shop that knows these cars. The guidelines are full tank of gas, car empty of junk (weight), spare tire/tool kit/jack (whatever the car came with) properly secured. Some shops use ballast to add weight to make up for the driver not being in the car others do not. Porsche AFAIK does not say to use any ballast. Oh and in one recent posting someone posted he sat in the car while it was aligned. Anyhow, I've had cars aligned with the weight, and without (mostly without) and I can't tell the difference and tire life was unaffected.

Now as to whether you want a mild sort of alignment or a more aggressive one I can't answer that. I know I prefer a car that feels connected to the road that doesn't wander about doesn't have a vague feel to the steering yet delivers given my style of driving easy 15K and up to 23K miles with even tire wear across the front tires' tread faces and across the rear tires' tread faces.

I will add that the best alignments, the ones that had me loving the car's feel while at the same time had the tires lasting forever (so to speak) the printout of the alignment graphic had the setting lines of each setting box right on the smallest hash mark in the center of the setting box.

I support all who suggest getting an alignment.

Do so at the best alignment shop in your area. My 986 had asymmetric rear tire wear on each tire. I brought the car to a high end custom alignment shop in the San Francisco bay area. They adjusted the alignment both front and rear wheels outside the factor limits for some parameters. I cannot remember which. I can tell you, however, I just replaced my Bridgestone 760s and the old ones wore absolutely evenly across each tire front and rear.

at the dealer. For the low, low price of $169.00 Cdn.

And I somehow think they aren't going to take me out for dinner, or even a drink, first.

What's the going rate for a reliable alignment in ROW?

I paid $190 US at the dealer yesterday. Quite a bit more than the last time. Glad I only do it every few years.

Thanks for the reference point. In comparison, the charge at the local Goodyear shop is about $80.