"Winter tyre" pressures - Page 1 - 911/Carrera GT - PistonHeads UK

Has anyone had experience here of running winter tyres on a 991? I have had my 991 Turbo S for a week now. I am running Pirelli winter tyres on the standard rims (245 fronts and 295 rears) but am finding that even under moderate braking the ABS is cutting in quite strongly. And not always on a damp surface. I know the brakes are huge and the weather is cold but I am still surprised by how little grip there is when stopping - especially front end grip. I am thinking perhaps the pressures are a bit high and wondering therefore what are the ideal cold pressures for running winter tyres. Mine are 2.4 f and 2.7 r.

I can't help with the TP's, but if you've not driven on winters before they can take a bit of time to get used to, and will also require a few hundred miles to 'settle down'.

Thanks for that....I have used winter tyres before but always on 4wd RS Audi's with much more weight/heat over the front wheels. I will try letting our some air and see if that helps.

If the tyres are brand new - and Trev's already said this, I know - you may find they need a few hundred miles on them to get rid of the release compound that's on them. You should find that braking in the dry at low temps isn't that far off summer rubber, and that wet braking may be better when the temp is low. I thnk you might need to give them a little while to get rid of their shiny coating... Of course, if you've had them a long time then I'm stumped, but I can't see tyre pressure making that much difference and you're not really running extreme pressures.

Interesting post Ernesto. I have a 997.2 4 GTS Convertible, and this is its second year on winter tyres. I put them on the car mid-November this year, I've noticed the ABS kicking in very easily and the car feeling generally rather unsettled on the road. Under heavy breaking or acceleration the back of the car snakes around. I've only noticed this in the last couple of weeks and not at all last winter or the three previous winters before that on my old 997.2 C4S. All have been running on Porsche approved and fitted winter tyres. They've been harvesting sugar beet near where I live in Norfolk, and all of the roads I used are quite muddy, so I don't know if that has anything to do with it. Philip

I started last year, and the running in period was a good 500 miles. The first 100 miles was almost scary, with little turn in. However, having got the pressures wrong at first, I can assure you the correct pressures do make quite a difference. They're not the pressures on the door - they're listed in the handbook. S

Interesting comments - thank you. The pressures I am running (2.2 fr) are correct according to the handbook although this does not say what size winter tyres this applies to. I have done ~200 miles now on the tyres and the ABS is still cutting in very early. Looking at the tread pattern on the front tyres there is perhaps 70% of the contact area compared to summer tyres. The tread blocks are also quite compliant - more so than the winter tyres on my Audi - so perhaps the Porsche winter tyres are a little more 'snow' biased. If you are progressive with the braking then no problem but we are so spoilt with modern Porsches that I/we forget about tghe importance of weight transfer on rear engine cars. I suppose the bottom line is don't drive the Turbo S on snow tyres like you would on summer tyres. Soooooo hard not to though.

Slight tangent, but what allowance are you making for ambient temperature? Would you expect much variation from the recommended pressure of 29psi 2.0bar with cold summer tyres when measuring a 20ºC day or at 5ºC?

I am setting the pressures cold so they are around 2.2-2.3 bar at 5-10C. With 'spririted' driving the pressures are up to 2.5 bar. You want some heat to soften the rubber and generate grip. But then again you don't want too much pressure as then you lose grip. Interestingly there doesn't seem to be an issue with traction. It is more an issue with absolute grip.

I am setting the pressures cold so they are around 2.2-2.3 bar at 5-10C. With 'spririted' driving the pressures are up to 2.5 bar. You want some heat to soften the rubber and generate grip. But then again you don't want too much pressure as then you lose grip. Interestingly there doesn't seem to be an issue with traction. It is more an issue with absolute grip.

Norfolkaston said: Interesting post Ernesto. I have a 997.2 4 GTS Convertible, and this is its second year on winter tyres. I put them on the car mid-November this year, I've noticed the ABS kicking in very easily and the car feeling generally rather unsettled on the road. Under heavy breaking or acceleration the back of the car snakes around. I've only noticed this in the last couple of weeks and not at all last winter or the three previous winters before that on my old 997.2 C4S. All have been running on Porsche approved and fitted winter tyres. They've been harvesting sugar beet near where I live in Norfolk, and all of the roads I used are quite muddy, so I don't know if that has anything to do with it. Philip I used to drive regularly on the roads North from Bury in the sugar beet season and remember the roads being like ice rinks, no matter what the temperature or weather. I'm on my second season on winters on my 997.2 C2S and am not finding any issue with early ABS cut-in (but as my discs tend to rust out rather than wear out, I'm maybe not the best person to comment there). What is noticeable is that the Sottozero winters (235/295/19" - same dimensions as the summers) do squirm around more than the summers and generally feel a little less smooth and subtle. But the cold weather grip and traction are fantastic. I'm currently running at the same pressures (2.3/2.7bar), measured and set at around 0°C rather than in the OPC's heated workshop!