Rear outside tire wear?

84porsche9113.2 · 06-10-2007, 01:19 AM

Before I ask, I did try to do a search in this forum on my question and although I found a lot of info on tire wear and alignment, I didn't find anything specific to my question...

I just noticed I have very uneven outside tire wear on the rear. I just noticed after maybe 3k-4k miles or so (i am not exactly sure when i got the tires but that's my best guess), that my rear tire tread wear indicators are showing on the outside of the rear tires only. The outside wear pattern appears the same on both rear tires -- only the outside wear indicator is showing and middle and inside wear indicators are still buried very deep in the tread. As far as I know, the tire wear on the front looks ok -- treadwear indicators are not visible at all, though I would expect this since the rears seem to wear faster.

In any case, I think I recall that the person who aligned my car last (he has a very good reputation for doing porsches) warned me that if I am not autocrossing or racing there's no need to go excessive negative camber on the rears because of increased tire wear (on the inside).

I do not autocross or race, but I do live up a windy hill and sometimes I do a little "spirited" driving up the hill. In any case, I called a tire alignment shop who was open today, and although they do not work on porsches, they said it was "very unusual" for a sports car to have outside tire wear on the rear and normally sportscars will have inside tire wear because of excessive negative camber.

My assumption would be my camber is not negative enough for the type of driving I've been doing. But I'm not really sure. I'm going to contact the person who did the align and find out what his opinion is. I read about that cambermax thing. But I don't think I need that excessive camber for just street driving?

It is a weekend and no one else is open now, so I figured I might as well try to get some other opinions while I am waiting... At the same time it may help others too.... Thanks in advance...

rnln · 06-10-2007, 07:55 PM

interesting, but sorry I can't help. Instead, I hope to hear more detail when you have the result.
Good luck.

84porsche9113.2 · 06-10-2007, 08:41 PM

Okay, actually I am mistaken. I took some close up pictures and now I realize that not only the outside was worn but the inside is worn about the same as well (it was just harder for me to see without getting all the way down near the tire). Being that I check my tire pressure regularly and run about 38 psi (these are 225/50/16's), I do not believe this a typical of underinflation pattern. My thought is that perhaps the inside is wearing due to negative camber, and the outside is wearing due to hard cornering.

The one thing that does puzzle me is that the center tread line is very deep and not even close to any of the wear indicators showing. I need to get a safety check in a couple of months and I don't want to fail because my wear indicators are showing on the outside, yet the center portion of the tire has a lot of tread left to go.

Is that just how it goes and I need to be replacing tires now since both inner and outer wear indicators are showing? Or can I keep the tires on longer being that the center wear indicator (and maybe the middle 70% of the tire) looks pretty new??

tonythetarga · 06-11-2007, 04:32 AM

That pattern is not normal and some spirited driving should not normally result in that much wear. You should ask the guy that did your alignment what settings he used. It might be you have both too much negative camber for the inside wear and too much toe in for the outside wear. If you get the numbers post them here as that will give you some feedback instead of guesses. If he doesn't know, you will need to have them measured to see what you have.

84porsche9113.2 · 06-11-2007, 12:53 PM

I went by today and the guy said the tire wear does look pretty even and that perhaps I should play with the tire pressure (increase) to get more wear out of the middle. I probalby am going to experiemnet with upping the pressure to about 40 psi. I'm running 225/50/16 on 8" wide rims. He also said that if I were running 7" wide rims I'd probably be getting more even wear, but because I have the 8's I'm gettin the uneven wear.

What does this mean? Does it mean I should experiment with a larger size like 245's to run the lower tire pressure (36 psi) since I have the 8's? I was told I should be running about 32psi from and 36 psi rear. I was also told in the past that the 245's are good for 9's but may be a little big for 8's...