Porsche have said I have the wrong size tyres on my car

My car was in for a bit of work and they said the Michelin pilot sports tyres on my car should be 295/30/zr/18 and the ones on atm are 285/30/zr/18. I've owned the car less than a year so its whatever the previous chap put on the car. Its a 2002 996 TT X50. Can you confirm this is correct please? ta

Obviously i'm just talking about the rears here

Tyre sizes should be in the owners manual. But if the rears are still good and you change them let me know as I have 285's on mine and might take them off your hands. TB

the one is brand new but it has a 1.5inch cut along the kerb protector. Its fine but I'm changing it for a forthcoming 'ring trip just incase I get a blow out at 140 mph I've tested it on a flat airfield and it hasn't popped at harsh 80mph cornering so should be ok. The other tyre is fine. You can have them if you collect from the Tyre place in birmingham next Wednesday

295 or even 315 would be correct but 285 works ok, little bit tail happy than obviously the wider option BUT 285 is cheaper to buy and more MPG's due to lesser road contact.

So a 315 would still fit on the same rim, lloyd? :? doesn't it like, bulge out?

Yes, you should have the number 10 next to your valve this denotes 10" wide rim, 10" will take 285, 295 or 315 The benefit of 315 on a 10" is a fractional bulge of the tyre wall which helps protect the rim from the curbs.

Great, thanks, just had a look and its a number 11 so 315 should slide on with ease, lol

Woaha.... Back to your original Q, 285 is incorrect, on an 11" rim it will be stretched meaning on heavy cornering you will be partly driving on the side walls. Take it easy and get onto 315's ASAP but get ready for the £580 bill :sad: Best price I got for P-zero N3 315/30 ZR18 was £289 fitted per tyre

I'd go with the recommended 295s if I were you. Unless you really like understeer, of course.......

Don't mess around with 315's, they are GT2 fitment which run on the 12" rim. Just get the correct 295/30/ZR18 which sit on your 11" rims. Suggest getting the same model tyres as you are currently running on your fronts unless you wanna change all 4.

Thanks for the offer but won't be around that area. TB

I'm with Richard H and ZeroH on this one :thumb: My 11j rear wheels have always had 295/30 18's fitted to them.

There is no way that any 4WD car in my opinion, should have anything other than the manufacturers spec fitted! Or at least tyre profiles front to back that give the wheels the same rolling circumferance! 315's on a 10" or 11" wheel would be a big no no!! 315 tyre (315mm) is just over 12.5", why would you try to fit this tyre to a 10" or 11" wheel? Standard wheels, definately 225/40 18 fronts and 295/30 18 rears! Buy the correct tyres, it'll be cheaper than a new transfer box!!!!

Just backing up my opinion 315 can be fitted to a 10" rim and look and perform fine however they are obviously more suited to 11" The extra width would have no impact on the transfer box and from experience had hardly any difference on the handling. You would need to be a serious track day driver to say that the difference is huge. Back in the days of running Nemesis performance we would often change tyre widths to see if we could shorten track time. On the 996 TT, it does as Richard H is possibly trying to point out handle quite well on the factory set up and therefore 315 rear may make the rear stay put but then cause under / oversteer but we are talking big speeds into bends to find this out, way more than 60 (or is it 50 max now on A - roads!!) on a fairly tight bend. 315's are £50 per tyre more, perform almost identical but look stunning from the rear.