Negative Camber

[Racedoc]

I have just replaced my tires after about 9,000 miles. When I took off the rear tires they were uneven in their wear pattern. The inside of the tires were down to the chord, with metal coming out, the outside of the tires still had tread. The front tires did not have this. This seems to be too much negative camber in the rear tires since I am more interested in street use than just track.

Has anyone else had this experience? If so did you have the dealer readjust the camber and did it run well on the street?

Thanks for any help.

[clord]

Hi Racedoc... The short answer is "yes". You posted in the 996 GT3 forum so I'll assume that you have a Mk II GT3 at normal ride height. Several things about GT3 alignment. The car is very sensitive to alignment and ride height. Many have been delivered from the factory with the alignment not within spec. The recommended alignment can be different for the street vs the track. Even for the street, factory alignment is such that the rear camber is some amount of negative and the inner shoulder of the the rear tires will wear more quickly than the outside shoulders in normal street driving. That's true for all 911s. All that said, I can get four 4-wheel alignments for less than the price of one rear tire.....so, my GT3 spends a lot of time on the alignment rack. For a street alignment, and to maximise the rear tire life, I run -1.7 degrees of negative camber on the rear and +0.25 degrees of positive toe-in per wheel in the rear. This is within the factory spec, but, at the minimum amount of negative camber and the toward the maximum amount of toe-in within the spec tolerance. My recommendations are in decimal degrees which most Hunter racks can report. The factory specs are in degrees+/-minutes, so you may have to convert. Did I answer your question?

BTW, 9K miles is pretty good for rear tires on a GT3...but, if you had steel belts showing, they were toast some time ago.

[Racedoc]

Hi Racedoc... The short answer is "yes". You posted in the 996 GT3 forum so I'll assume that you have a Mk II GT3 at normal ride height. Several things about GT3 alignment. The car is very sensitive to alignment and ride height. Many have been delivered from the factory with the alignment not within spec. The recommended alignment can be different for the street vs the track. Even for the street, factory alignment is such that the rear camber is some amount of negative and the inner shoulder of the the rear tires will wear more quickly than the outside shoulders in normal street driving. That's true for all 911s. All that said, I can get four 4-wheel alignments for less than the price of one rear tire.....so, my GT3 spends a lot of time on the alignment rack. For a street alignment, and to maximise the rear tire life, I run -1.7 degrees of negative camber on the rear and +0.25 degrees of positive toe-in per wheel in the rear. This is within the factory spec, but, at the minimum amount of negative camber and the toward the maximum amount of toe-in within the spec tolerance. My recommendations are in decimal degrees which most Hunter racks can report. The factory specs are in degrees+/-minutes, so you may have to convert. Did I answer your question?

BTW, 9K miles is pretty good for rear tires on a GT3...but, if you had steel belts showing, they were toast some time ago.

Thanks this is what I ws looking for. So it sounds like this is a legal charge from the dealer to make the adjustment for street use.

[clord]

Thanks this is what I ws looking for. So it sounds like this is a legal charge from the dealer to make the adjustment for street use.

I'm not quite sure what you mean by "legal charge", but, what I recommeded is within the factory spec tolerance, but, toward the end of the tolerance that will maximise tire life for the street. If you suspect that the alignment was incorrect from the factory, you may be able to convince the dealer to check/adjust it under warranty. You will also need to talk to the alignment rack operator to see if he will agree to get the result as close to what you want as possible. Setting the camber and toe on the rear is not easy and some operators will quit when they just get it "somewhere in the tolerance range". I go to a rack run by my favorite tire dealer who understands my...uh.... obsession...with getting it right and lets me hang around and sit in the driver's seat while he works so that the result is what I want with me driving the thing. And remember, you can get 4 to 6 alignments for the price of a set of rear tires. A good alignment shop is hard to find. Take care of them when you do find them.