Tyre Pressures
- Thread starter Guest
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Guest
New member
Hi Jeff,
You may get some recommendations, but there is no definitive for your car as the sizes are not standard (assuming you consider factory recommendations definitive[
]).
While I am aware that the factory tends to recommend quite high rear pressures, I have never received a satisfactory explanation as to why. Remember that the higher the pressure the smaller the contact patch and the less grip (simplified analysis) - so why do we want less rear grip?
I personally like to stick to slightly lower pressures in the rear otherwise I find that the centres wear a little quickly - like 32-34 rear and 29-31 front.
As another data point, the guys at Silverline, in the context of PZeroCs, said run at 36/34 on the road and 33/30 hot on the track. So only 2-3 psi differential between front and rear.
HTH
Richard
You may get some recommendations, but there is no definitive for your car as the sizes are not standard (assuming you consider factory recommendations definitive[
]).While I am aware that the factory tends to recommend quite high rear pressures, I have never received a satisfactory explanation as to why. Remember that the higher the pressure the smaller the contact patch and the less grip (simplified analysis) - so why do we want less rear grip?
I personally like to stick to slightly lower pressures in the rear otherwise I find that the centres wear a little quickly - like 32-34 rear and 29-31 front.
As another data point, the guys at Silverline, in the context of PZeroCs, said run at 36/34 on the road and 33/30 hot on the track. So only 2-3 psi differential between front and rear.
HTH
Richard
Guest
New member
I have run 29/36 for some years now, on my 205/245 tyres on 7/8, with no abnormal wear. I assume the high rear pressure is due to the high rear weight/rear wheel drive/tendency to squat on acceleration; it does not seem to compromise grip, if the tyres wear evenly across the surface.
The manual suggests 29psi front and 36psi rear. I run at about those levels cold and gradually reduce for track days (to keep at or near the factory spec). Seems to work ok with pretty even tyre wear.
Jamie
Jamie
Guest
New member
Simon, tyre pressures are much debated. I personally think that 36psi (rear cold) is too high and many agree. Nobody (IMHO) has satisfactorily explained why Porsche specifies what most people think are abnormally high rear tyre pressures. The rear weight bias alone is not enough - we already have a bigger tyre for that.
I run 32-33psi rear and 29psi front. My experience on track shows that you need even less font/rear differential if you want to end up with correct hot pressures.
If you search in the last 6-9 months, you will find plenty of posts on tyres and pressures on this board.
FWIW, my opinions are basically the same as the consensus on Pelican and Rennlist boards - so I am in pretty good company. I am not just making this stuff up.
Richard
I run 32-33psi rear and 29psi front. My experience on track shows that you need even less font/rear differential if you want to end up with correct hot pressures.
If you search in the last 6-9 months, you will find plenty of posts on tyres and pressures on this board.
FWIW, my opinions are basically the same as the consensus on Pelican and Rennlist boards - so I am in pretty good company. I am not just making this stuff up.
Richard
Guest
New member
Depends on the tyres. Some R-compounds like no more than 32psi hot for track work, some like high 30s. For road tyres on track I like no more than 35/36psi hot which means starting at 30ish cold. On the road I use something like 29/32 split cold but it depends on how the tyres are wearing etc. The only hard and fast rule I have is to run a bit lower than the ludicrously high pressures that Porsche recommends for rear tyres - but YMMV.
HTH
Richard
HTH
Richard
Guest
New member
Depends on the tyres but you must check hot pressures straight after a session rather than rely on cold pressures.
As a guide, try no more than 36psi hot for road tyres and no more than 32psi hot for track tyres. You may like a slight front rear differential of say 2 psi higher in the rear but there is no real need or logic to it on track. Cold pressures will be anything from 4 to 10 psi lower than hot temps.
As a guide, try no more than 36psi hot for road tyres and no more than 32psi hot for track tyres. You may like a slight front rear differential of say 2 psi higher in the rear but there is no real need or logic to it on track. Cold pressures will be anything from 4 to 10 psi lower than hot temps.
Mmmmnnn?
Why if the cold road press are say 2.0bar fr,2.5Bar rear would you not want a front rear difference on track? ( 29/36PSI)
I find that on track the rears heat up more so I have to let more air out to avoid overheating, but i still have to admit I am confused as to why Porsche recommend a pressure differential of 6 psi cold fr/rr.
I know you will have an opinion on this RB, I look forward to your reply.
PS on track tyres i do tend to adjust to optimal press/heat wether front or rear
Why if the cold road press are say 2.0bar fr,2.5Bar rear would you not want a front rear difference on track? ( 29/36PSI)
I find that on track the rears heat up more so I have to let more air out to avoid overheating, but i still have to admit I am confused as to why Porsche recommend a pressure differential of 6 psi cold fr/rr.
I know you will have an opinion on this RB, I look forward to your reply.
PS on track tyres i do tend to adjust to optimal press/heat wether front or rear
Guest
New member
For track use, I don't understand the front rear differential pressures either and have always aimed for even hot pressures all round - unless using the pressures to finetune under/oversteer balance. For road driving I guess the assumption is you are putting air in purely for supporting the car's weight in which case the higher rear pressure makes *some* sense. Porsche recommended rear pressures are too high and have been widely discredited in the context of fast road or track driving, IMHO.
dtunnicliffe
New member
Kristian,
you don't say what size tyres they are but I'm assuming they are 17" plus. I'd be tempted to drop the rears to 35 psi (perhaps 2.2 to 2.5 bar) and the fronts to 30 psi (2 bar). You are very close to the limit on the rears at the moment and once they heat up you could be in trouble. You are bound to run rough on bigger wheel/tyres since there is less air/rubber between you and the road and the noise tends to rise accordingly. To be sure, I'd talk to an OPC since they fit pretty big wheel/tyre combinations as standard.
Dave
you don't say what size tyres they are but I'm assuming they are 17" plus. I'd be tempted to drop the rears to 35 psi (perhaps 2.2 to 2.5 bar) and the fronts to 30 psi (2 bar). You are very close to the limit on the rears at the moment and once they heat up you could be in trouble. You are bound to run rough on bigger wheel/tyres since there is less air/rubber between you and the road and the noise tends to rise accordingly. To be sure, I'd talk to an OPC since they fit pretty big wheel/tyre combinations as standard.
Dave
phil pullinger
New member
Hi,
I think you have it spot on there, but if you look at the gold coloured labels on the engine bay it says 2 bar front 3 bar rear.That is actually 29psi front 43 psi rear.The front is acceptable but 43psi rear is , i think way too excessive.
I think you have it spot on there, but if you look at the gold coloured labels on the engine bay it says 2 bar front 3 bar rear.That is actually 29psi front 43 psi rear.The front is acceptable but 43psi rear is , i think way too excessive.
has there ever been an official explanation from Porsche/other expert as to why they quote such high rear tyre pressures for 911's? Are they really meant to be that pumped up? I noticed same for both my current 3.2 and previous 964.
I remember trying the Porsche recommended psi for the rears on my 964 (think it was 44psi) and it made the rear seem rock hard and uncompromising..not to mention asking for a puncture on rural lanes. Did make it a tad more oversteery that i liked though []
I assume Porsche know what they are talking about so just wondered why they recommend such high pressures.
I remember trying the Porsche recommended psi for the rears on my 964 (think it was 44psi) and it made the rear seem rock hard and uncompromising..not to mention asking for a puncture on rural lanes. Did make it a tad more oversteery that i liked though [
]I assume Porsche know what they are talking about so just wondered why they recommend such high pressures.
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