J.Graham

I was changing my wheels the other night. Putting on the cup 2's for the winter. When I removed the rear wheels, I was surprised to see the inner edge of both my rear tires ground down to the cords! The front tires still have plenty of tread (my understanding for replacement is 2 sets of rears for every set of fronts). It looks as though they have been rubbing but I can't see any evidence of that in the wheel-wells.

I am running Factory MY02's with Michelin Pilot Super Sports (265/35/18).
Ride height is around RS + 10 (maybe a touch higher).
Rear Camber Settings- Left -2.1 Right -2.0
Tires- Installed April 28, 2011
PSI- Rear 36 & Front 34
Miles driven on tires- 8,700 (14,000 Kms).
Suspension Set-Up- PSS-10's (set at 5 front & 7 rear) with H&R Sways.

As you can see from the pictures- the cords are exposed on the very inner edge.

My questions;
Is this normal wear for the rear tires? (I don't spin them but I do DRIVE the car).
Anyone else had this experience?
Is this a Rubbing Issue? (I can't see any signs of rubbing in the wheel-wells).
Is this a Camber issue?
Any thoughts, input or recomendations would be greatly appreciated. I'd like to purchase another set of rears for next season but I'm a little hesitant now!
Thank you.

ca993twin

Welcome to the world of rear engined Porsches! You MUST keep a closer eye on those inside edges... that is normal wear from an aggressive (quite negative) rear camber. After you mount some new rears, you may have a good alignment shop (one that understands kinematic rear toe) dial in a less aggressive camber (unless you track your car). Its possible that your tires can be dismounted and flipped halfway through their wear to give longer life.

NP993

You have -2 degrees of rear camber....were you expecting even wear?

Mike J

Nothing to do with rubbing on the car, its the rubbing on the street that is the issue..!

With -2 and if your car is low its often hard to get the toe dialed in due to the length of the control arms (you will be close to their limits, but it should be OK). Do you know if the rear toe was dialed in right?(as pointed above, you need to understand the dynamics of the rear and have the proper tool to do a good alignment). For street use I would straighten the wheels to -1 to -1.2, and then do the toe to the factory spec.

BTW, you got 14,000 km on a set of rears - that is pretty good actually. Replacement tires are cheaper in Bellingham.

Cheers,

Mike

certz

Negative 2 degrees on a street car (you did not say if you track the car) is very aggressive IMO especially if you are looking for tread life. I run 2.5 all around on the track car, but it sees very little street driving. I agree with the above, that you should have your shop take some camber out - I believe between 1 and 1.5 is typical for street application depending on how aggressive you want it.

brad@tirerack.com

What he said!

nile13

8,700 miles on the rear of 993 is way too good a result for a soft compound tire. With 2 degrees of rear camber the chord being nice, shiny and so nicely visible is no surprise.

I'm not sure why you need that much camber on the street. I'm also not sure how you could miss that much wear unless you pay no attention to the tires at all (happened to me on a 4,600+ maiden voyage across the continent in my newly purchased first 993 with pretty new tires).

Cactus

You have at least two more trips around the block in those......

trophy

Our cars are more sensitive to toe on tire wear than camber. You can quite easily run -2 If your toe is in spec. For a street car i would set camber between -1.2 and -1.5, and and set toe to factory. Also male sure they shop doing the work knows how to check and adjust Kinematic toe. I always ask the shop what Kinematic tool they use (Porsche Factory or Motorsport) if they look at me with a blank stare, i leave and head to another shop.

What are your toe settings? As Mike said, when the car is low, it is more difficult to get toe back to spec with stock links.

I run close to -3 on the rear and don't get this type of wear, my Toe is perfect. If i have too much toe, I can start to see rubber dust on the rear bumper.

Toe is much more important to get right than camber. If you have too much camber with too much toe then it's a double wammy....

J.Graham

Thanks for all the replies guys- I feel much better now
Too funny- as I'm looking at the invoice for the allignment done on the car in April 2011, it states "THESE SETTINGS WILL INCREASE TIRE WEAR". I did take it to a shop that specializes in Porsche Racing!
I'm not concerned about getting more life out of my tires and I have to say that I love the way my car handles- so I'll probably just stick with this set up the way it is.
I will keep a closer eye on them though!
Cheers

J.Graham

You guys are too fast...
Here's the allignment sheet with all the specs.

trophy

Total toe is within the stock range, right toe is on the pretty close to the upper range of spec. I always like to see equal both side's, (2.5 vs 1.9 is little to much difference for me, but within spec) but that is just me.

I think their specs are a little out, max of 3.1mm is about 17 minutes, the porsche spec is 10 minutes +/- 5.

I run my car at 1.5mm per side or 3mm total.

Mike J

For those settings you are getting good mileage out of the back. Steven is right, toe is a bit strong.