New tyres fiited - handling is now real bad !!

Just had 2 new rear tyres fitted - 265/35 ZR 18 N4 ROSSO, have done about 200 miles since fiited last week. The car is now 'twitching' from left to right ! Have just all the wheels for correctly torqued bolts and tyre pressure ( as per the handbook ) Should I contact the outfit that fitted them...... ? Mark

Yes. Presumably you have N4 Rossos on the fronts? I wouldn't trust a tyre fitter to adjust the geometry on a Porsche, so if you are still not happy, best to have this done at the dealership and ask them to notify their Pirelli rep in case one or both tyres have a defect (unlikely though).

Are they both fitted the right way round? These have a correct direction to rotate I believe?

My thoughts too!! Also check the pressures, book cold of 44 is far to high, IMNVHO. Melv

What do you reccomend Melv ? been trying to get pressures right for a while & can't seem to find the right balance. Julian.

No I don't have N4 ROSSO's on the front! Have been back and as a gesture they are giving me a discount on the fronts - £118 inc vat, fitting and balance. Melv..... will it really make that much difference ? Why is 44psi to high from cold, what should I aim for ? Thanks Mark

I had an experience where i had new tryes fitted and took the car back a few days later as the car was vibrating, I was assuming i had balance problems. The fitter was the same guy, he remembered me and told me that when i pulled away from the garage i accelerated briskly infront of a car (at a roundabout) and would have spun the wheels inside the tyre hence the balance would be out ! He was right [ ] NOTE , tyres do need time and heat to bed in Maybe not related but worth remembering anyway [ ]

Mark -try 36 all around. I found 44 far too skittish. And you MUST have matching tyres, including N ratings, on all four wheels. Melv

Melv, Dropped the rears to 40psi this morning and it did feel better, will drop them again tomorrow before my journey. Getting the front tyres changed this week so should be better ? I know 36 psi all round is okay for 17", but is that too low for the rears on 18" rims ? On renlist there has been some posts suggesting 32(F)/39(R) and 34(F)/39(R) Mark

Mark. Yeh, go with the Rennlist recommendations. I'm sure u will notice the difference when u change the fronts. BTW, may have missed it in thread, but when was the last time a full four wheel geometry check was done on the vehicle? Rgds Mel

Just for info, and I wouldn't claim to be "right", but I use 2 PSI down on the book figures, so 42(r) and 34(f) at the moment. I mostly drive on motorways though, so don't generate as much heat as going down a windy lane, although in the summer I may drop it another 1-2 PSI more. The tyres are wearing quite evenly, but then the C4S is 115Kg (8%) heavier than a C2 and 65 Kg heavier than a C4.

I think this has been discussed before but if you play around with your pressures, then go have an accident, you could find yourself in an interesting discussion with your insurer..... Scene opens with you and a suited guy with big frown and clipboard surveying an unrecognisable heap of twisted metal..... "Look hear, Let me jolly well tell you Mr Norwich Know-all Union.... forget what Porsche tell you 'cos a bloke I know called Melv told me it would go better when I dropped 8psi out of the ole' rears and yes it was worth £45k so there" Not disagreeing with anything said so far but perhaps this is just the job for PCGB - getting together with PGB and agreeing to the issue of some sort of Technical Memorandum that would cover us all. I cannot see it happening because of the legal implications. You can see from the number of non-technical questions on here (some very humerous) that there are a large number of non-petrolheads on this forum who might, in a moment of total stupidity, play around with things on their cars that could lead to potentially fatal results.... Gosh I feel all funny - I was actually serious for a moment......

Good point, although if you go on the basis of tyre wear, then if it is even it can't be too far wrong. In any case, if you are no more than 10% out from the spec, then they would have a hard time proving anything, since this is a "normal" variation depending on ambient temperature. I think you would only have a real liability issue if you were substantially under or over pressure.

For years I've run my Porsches at 10% below the recommended pressures for road use, and my OPC always stick to my pressures. I think Peter Robinson did the same on his long-term 996.