Abnormal tyre wear....or not?

[robbosliding]

Had my wheels off my 996 C4S today and saw that my tyres don't have as much life in them as the outer visible area had led me to believe.
The wear is not even across the tyre but is symmetrical in relation to the other rear tyre.
The low wear indicators in the grooves on the outer third of the tyre indicate 2mm of life left. The other section of the tyre is worn down almost to the wear indicators. The inner edge is not wearing excessively (like I have seen when tracking is out) so I have wondered whether it is a tyre pressure issue or geometry set up. I have read other posts regarding geometry set up but I don't have much knowledge of it. My understanding of it is that it is the angle that the shocks are set up at to present the tyre to the road surface. Therefore incorrect angles should show excessive wear on inner/outer but how does this account for the inner two thirds???????
Can anyone shed any light on this before I fit new tyres and do the same again?

 

[Richard_Hamilton]

It sounds to me like you have too much negative camber at the rear. If the car hasn't had a geometry check in the last couple of years, I would suggest you get it checked.

 

[NXI20]

Notwithstanding what Richard has said, I would also comment that:

1) A 2mm difference in wear between the inside & outside isn't that dramatic over the life of the tyre.
2) If you tend to do a lot of motorway miles, this sort of wear pattern is to be expected anyway.

 

[robbosliding]

Thanks to both of you for your input. I tend not to do motorway miles as such, more A roads and sweeping twisty local B roads. For reference I am running Continental N2 tyres at 44 psi which certainly falls in with Richards previous advice (not withstanding he use pirrelli's). Can anyone explain why this wear pattern would "fit" motorway mileage?Is it to do with opturating effect or lack of cornering?
Should this have been some thing an annual inspection should have picked up, it was only done 2 weeks ago. Either way it does not change the fact it is happening but I would like to know if any adjustment in geometry or otherwise is required.

 

[NXI20]

There is a small amount of negative camber on the rear as standard. When travelling in a straight line this means that the inside of the tyres carry more load than the outside. When cornering, the load is mainly carried on the outside of the tyre and so use on bendy A & B roads will tend to wear the tyres more evenly than doing huge miles on straight motorways.

This is obviously very simplistic - people write books about suspension!

 

[robbosliding]

Thats all understood, thank you very much.
Must put one of those suspension books on my to buy list........

 

[Brian RS]

We would probably all be happy to have such tyre wear.
The "toe in" may cause this but in any event Porsche tell us to change tyres
with 3mm remaining!

 

[robbosliding]

Nick, by all accounts you were absoloutely right. Had my new conti s fitted today and discussed the wear on the old. Fella swapping the tyres said they had worn incredibly well for a rear wheel drive so no problems. Price for reference was £360 fitted at Lincoln Tanvics tyres. Good price and good service.

 

[Diesel130]

... so you'll just have to drive faster round those bends !

 

[NXI20]

What he said []

Mine wear more on the outside, despite having 3 degrees of -ve camber at the rear. The fronts run 7 degrees and still wear more on the outside edge.

Can't imagine why []

 

[Richard_Hamilton]

I run the standard settings on mine, and both fronts and rears wear perfectly evenly across the tread. Matthew, if you haven't had your geometry checked, I would recommend you get it done. Peace of mind, and if it is out you will certainly notice the difference in the way the car feels.