Philster

This might be more of a sanity check, because I am working from the premise that when I see the inboard side of the rear tires wearing faster than the outer half, I think ''alignment''.

I want to double check here, because there is, seemingly, no end to the 'Yeah, but on a 997, it is____________________' type of qualifying statements.

So far, two shops have told me that rear inner half tire wear is a product of independent suspension (umm... well, if done wrong, sure) and the 997 linkage.

Quite frankly, I'm skeptical.

I don't want to add spacers (I just received the recommended sizes courtesy of Sharkwerks) and make the issue even worse.

Tire pressures are 2-3 lbs below the door placard, as this car is always lightly loaded.

1990nein

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Quadcammer

you have negative camber on your rear suspension, hence, you will see more inner tire wear. That said, it can be aggravated by bad toe settings, or an alignment that is just too aggressive for your purposes.

If its not dramatic, i'd call it a non issue.

chuck911

Philster, you are right to be skeptical of the inadequate explanations you've been given. The truth is all cars are set up with suspension geometry aligned to deliver whatever the manufacturer feels is the best compromise for the intended drivers use. "Compromise" covers performance, comfort, tire wear- everything.

Now a 911 simply has to deliver a lot of superb high performance handling, a fact which demands (among other things) a fair amount of camber. Simply stand back and look, you can see the angle. Obviously (I would hope!) this angle is going to increase tire wear on the inside edge during straight line driving. Hard cornering on the other hand increases tire wear on the outside edge, which the camber angle tends to reduce.

Putting it all together, if you balance out your straight line driving with your hard cornering- and if this balance matches your suspension alignment- then you will experience even tire wear. Too much freeway, too much inside wear. This is what Quadcammer means by "too aggressive for your purposes."

Bruce In Philly

I would agree except for the fact that I stopped my inner rear wear on my car by changing the alignment specs just a bit. Given the large amount of miles I put on my car, I see it as a real money saver. I now have perfectly even wear on my rears 2009 C2S.

The most common reason for inner wear is toe being out of spec. The second, according to a few including me (others don't agree with this) is the large about of negative camber Porsche specs in rears. Notice the tires are canted with the tops in and bottoms out.

I had the car re-aligned and had zero toe and as much of the negative camber removed as they could. The result is the rear camber is still negative but a bit out of Porsche spec (so I am told). Today, my rears are wearing perfectly even both on my 18" winters and 19" summers.

I also asked for more negative camber in the front..... this combo livened up the handling as I thought it was pretty dead and boring with factory specs.

My approach is not a track approach..... very different.

To be open about this, some have said the removal of negative camber was not the reason I am getting even wear, it was moving the toe to zero. YMMV

Peace
Bruce in Philly

Quadcammer

Right, its a balance, like anything else.

We don't know how dramatic the OP's inner wear is. A little bit more wear on the inside is not something I'd concern myself with, but if he is grinding the inside down to the cords in 8k miles, while the rest of the tire is fine, he likely has a toe issue.

Furthermore, if he has a track alignment and drives mostly on the highway, that will also give him some inner wear issues.

more info and maybe pics are needed.

BIG smoke

No suspension changes from factory so far?
How many miles on your tires?
How old are the tires?
What kind of tires?
From what kind of driving style and where?
City is going to chew through tires, vs long highway drives?

Philster

Stock 997S suspension.... 19" 295 Bridgestone Pole Positions A/S (unfortunately).... RE970AS.... Tires have 8k miles on them... are 18 months old. I'll try to get some pics and some measurements.

I am keenly aware of negative camber, and this is why I checked here: Yes, if there is actually enough negative camber from the factory that inner wear is going to happen first for many drivers (other than track stars), and this is a handling setup likely to wear the inner tread first, then I'm not going to make any changes at the sake of handling, I'm choosing handling every time.

I'm about to get extreme summer tires or have them ready for spring.

My car does nothing other than serve the purpose of hard/spirited driving. But just to get anywhere to torture the outer tread, miles are being rolled off on highways, etc. I'll gladly wear out the inner treads first to preserve the max handling.

So, they type of feedback I was looking for that would raise concern would be things such as, "I've got a stock 997S and it's a daily driver with standard camber and toe settings from the factory, all highway miles, and my tires always wear evenly." .... then I'd go, "Hmmm..."

.

JW911

I replaced my tires a few months ago. The rears were worn down to the cords on the inside. Only about 8,000 mile and I had to replace. The outside had a lot of life left. I had an alignment done and I instructed the shop to set the camber to the minimum negative camber while remaining in spec. He did make a fairly substantial adjustment. We'll see how that goes. Also, I suspect my 15mm rear spacers exacerbated the problem because I never saw the cords on my previous tires when I had no spacers.

Petza914

On my wife's 2005 C2S DD she was getting quite a bit of inside rear tire wear and doesn't need an alignment setup for spirited driving. Attached is the alignment report from when I installed her new set of tires and had the alignment tech adjust the rear camber and toe for better rear tire life. After 12,000 miles with these new settings the rear tires are wearing very evenly across the full width, and it's easy to tell, as her tires have wear dots built into the tread pattern.

semicycler

Too much toe kills tires. Your results are good but could be even better. Looking at your alignment spec doc, your before rear toe was on the high range to slightly out of spec. This was causing all of your rear wear. Your before rear camber was also on the high side of the spec, which lead to rear inner wearing unevenly.

Your after toe is now in the middle of the range but rear camber is below spec. For even better wear to performance specs, get your rear toe as close to zero as possible while still being in spec, 0.04 in for this case, and reset your rear camber to the lower spec of -1.3 degrees. You will get even better wear results and even better cornering than you are seeing now.

Petza914

Thanks for the info. I was afraid to make too big a change at one time, not knowing what the effect of the handling change would be, and didn't want to make the car unstable or unpredictable since it's my wife's DD, but now that I have your input and advice on what the settings should be, I'll make those changes at the next alignment.