Tyres at 45psi for track days!
Discussion
Spoke to an experienced track day driver and autocrosser recently about tyre pressures on track days. He owns a 993TT.
Our local track is usually hot and dry, with occasional sand drifting across. He drove a Ferrari 360 on the circuit and experimented with tyre pressures as the Ferrari was very nervous. Interestingly he found that upping the pressures by around 10psi made the car much more stable and recommended I do the same to my GT3 to counter the effect of sand on the surface.
Now, I respect this guy's opinion a lot as he's an accomplished racer, but that seems somewhat daft to me.
As per usual Porsche practice, my normal approach is to drop the front tyres to around 26 cold (or approx 32 hot) to get more bite at the front and drop the rears to around 34 cold (approx 40 hot) to stop the back end moving around too much.
Does anyone recommend I go with his advice? I have already had a couple of spins at this track (one at high speed), both attributable to a split-friction surface (one side slightly dusty, the other dry).
Our local track is usually hot and dry, with occasional sand drifting across. He drove a Ferrari 360 on the circuit and experimented with tyre pressures as the Ferrari was very nervous. Interestingly he found that upping the pressures by around 10psi made the car much more stable and recommended I do the same to my GT3 to counter the effect of sand on the surface.
Now, I respect this guy's opinion a lot as he's an accomplished racer, but that seems somewhat daft to me.
As per usual Porsche practice, my normal approach is to drop the front tyres to around 26 cold (or approx 32 hot) to get more bite at the front and drop the rears to around 34 cold (approx 40 hot) to stop the back end moving around too much.
Does anyone recommend I go with his advice? I have already had a couple of spins at this track (one at high speed), both attributable to a split-friction surface (one side slightly dusty, the other dry).
Not a Porsche expert at all but my trackday experience tells me upping the pressures is the norm. You need to experiment, setting them from cold is always difficult as you can only adjust/experiment with them on track when hot (then see what the cold temps are once cooled down which will take some time)
5+ psi when hot is quite normal & would be a good starting point in my book.
5+ psi when hot is quite normal & would be a good starting point in my book.
I started with not knowing buggar all about tyre pressure on the track once ( still the same) and didn't lower the pressure. Started with the recommended 36 F+B, after 4 laps, the pressure went up to over 45, rubber was beading and falling apart! told by the guy on the track to lower it, to 36 when hot (@28 cold), the car handled 100%better and the rubber looked ok then (just wearing normally)
cptsideways said:
Not a Porsche expert at all but my trackday experience tells me upping the pressures is the norm.
Now perhaps I'm wrong, but on a track day I LOWER my pressures by up to 4 psi when cold. The tyres heat up and the pressure rises, ergo if you raise them then the pressure inside will increase....
Am I doing the wrong thing??????
Particularly with the 911 on track, with the weight at the rear and heat generated, track tyre pressures are going to rise.
Porsche reccomend 36/44 for my 993 with 18" wheels...
curiously Porsche seem to have reccomended these pressures on 964...through to late 996...all different cars in terms of weight and output ?
Through experimentation and talkng to other Porsche driver over the years I now use F33 R36 on the road and on track when hot, I use 32 psi for both front and rear......as you can imagine this means letting quite a lot out of the rears.
For your Gt3 I would not pay any attention to the reccomendations of a TT owner,, these cars are heavier and obviouly have 4wd, so the characteristics would not suit your car.
If you don't get a response on here from a Gt3 owner who tracks regularly, I would suggest you look to the PCGB forum or www.titanic.co.uk...this is where they post.
>> Edited by clubsport on Monday 7th February 09:40
Porsche reccomend 36/44 for my 993 with 18" wheels...
curiously Porsche seem to have reccomended these pressures on 964...through to late 996...all different cars in terms of weight and output ?
Through experimentation and talkng to other Porsche driver over the years I now use F33 R36 on the road and on track when hot, I use 32 psi for both front and rear......as you can imagine this means letting quite a lot out of the rears.
For your Gt3 I would not pay any attention to the reccomendations of a TT owner,, these cars are heavier and obviouly have 4wd, so the characteristics would not suit your car.
If you don't get a response on here from a Gt3 owner who tracks regularly, I would suggest you look to the PCGB forum or www.titanic.co.uk...this is where they post.
>> Edited by clubsport on Monday 7th February 09:40
I'm no 993T track pressure expert, but feck me that sounds way way too high, esp as it sounds like you are out is some Arab state where the track temps will be somat crazy no doubt.
Does the fella mean run at 45 or start at 45? (i.e they will go up even more with the heat)
I think with the power/torque plus the weight of a 993T sliding about, that running at those pressures would not only make the car feel uncontrolably twitcy beyond belief & the sand on track would multiply that factor.
EDITED TO ADD-
DoH! read the post properly next time!
ahh I see you have GT3 & its matey with the 993T, Doh! oh well 45 still seems high, but try it (carefully)& see how you get on? My money is on it feeling worse tho.
>> Edited by iguana on Monday 7th February 12:35
Does the fella mean run at 45 or start at 45? (i.e they will go up even more with the heat)
I think with the power/torque plus the weight of a 993T sliding about, that running at those pressures would not only make the car feel uncontrolably twitcy beyond belief & the sand on track would multiply that factor.
EDITED TO ADD-
DoH! read the post properly next time!
ahh I see you have GT3 & its matey with the 993T, Doh! oh well 45 still seems high, but try it (carefully)& see how you get on? My money is on it feeling worse tho.
>> Edited by iguana on Monday 7th February 12:35
Other than cosworth (you mentalist!) I would say the received wisdom is to do the normal 911 thing, that is let the air out gradually to maintain 32/36 hot or similar.
This chap reckoned the ultra-high pressure allows the tyre to get better purchase on a dusty surface, but I'm honestly too scared to experiment with those kinds of extreme pressures. I will keep an eye on his progress next time, and maybe try a careful one-lap experiment.
Thanks for all the replies.
This chap reckoned the ultra-high pressure allows the tyre to get better purchase on a dusty surface, but I'm honestly too scared to experiment with those kinds of extreme pressures. I will keep an eye on his progress next time, and maybe try a careful one-lap experiment.
Thanks for all the replies.
on a serious note, all cars even if there the same model and spec are different weights and have different suspention charictoristics. there is no right or wrong answer, just what works for you. as long as your guess isn`t wildly out, you won`t be suffering a blow out or begging the tyre shop for more rare and imported tyres.
Well I may as well throw my penny in. I've experimented on several occasions and the results of lowering the pressure in my 993TT have always been the same; increased understeer and the tyres seem to 'go off' after four or five hot laps.
Leaving them at 36 44 (cold) and the car is neutral and progressive.
I run SO2's.
Leaving them at 36 44 (cold) and the car is neutral and progressive.
I run SO2's.
After ten years of tracking 944S2, 964C4 and Cup Car, for the former two the 32-36psi hot seems to work. BTW, cold pressures after a track day were about 25-26psi.
After some experimentation at Castle Combe a few years ago, John Miles and I found that the increase in tyre pressure on standard C4's was about 8-10psi on the rears after an early track session -constant lowering of the pressures saw about 36psi consistantly as the day wore on.
The only time I would increase the tyre pressures is when it is wet as this dissapates the water quicker allowing the centre of the tyre to cut through the water, but only by a couple of pounds or so.
I now run the Cup Car on slicks, but on Bridgestone S02, 32 psi hot all four seemed to work, but an increase of only 1-2psi made the back end (double entendre intended) a little loose. But bare in mind it only weighs 1120kgs.
Your mates pressures sound like uneducated bar-room chat to me, I'm afraid!!!
Understeer? Try a tad more neg camber at the front, strut brace and a full tank of fuel!!
Rgds
Mel
>> Edited by Melv on Monday 7th February 16:52
After some experimentation at Castle Combe a few years ago, John Miles and I found that the increase in tyre pressure on standard C4's was about 8-10psi on the rears after an early track session -constant lowering of the pressures saw about 36psi consistantly as the day wore on.
The only time I would increase the tyre pressures is when it is wet as this dissapates the water quicker allowing the centre of the tyre to cut through the water, but only by a couple of pounds or so.
I now run the Cup Car on slicks, but on Bridgestone S02, 32 psi hot all four seemed to work, but an increase of only 1-2psi made the back end (double entendre intended) a little loose. But bare in mind it only weighs 1120kgs.
Your mates pressures sound like uneducated bar-room chat to me, I'm afraid!!!
Understeer? Try a tad more neg camber at the front, strut brace and a full tank of fuel!!
Rgds
Mel
>> Edited by Melv on Monday 7th February 16:52
Thanks Melv et al. As usual PistonHeads delivers. I know this is all stuff that has been done to death many times over, but it helps to remind oneself of the difference between idle bar-room chat and informed opinion.
On a slightly different note, my wife said to me yesterday, "Say hello to your NerdHeads from me."
"Eh?" says I.
"NerdHeads, you know all those sad people who talk about tyre pressures."
"Tyre pressures, er, I don't know what you're talking about...."
On a slightly different note, my wife said to me yesterday, "Say hello to your NerdHeads from me."
"Eh?" says I.
"NerdHeads, you know all those sad people who talk about tyre pressures."
"Tyre pressures, er, I don't know what you're talking about...."
Harris_I said:
Thanks Melv et al. As usual PistonHeads delivers. I know this is all stuff that has been done to death many times over, but it helps to remind oneself of the difference between idle bar-room chat and informed opinion.
On a slightly different note, my wife said to me yesterday, "Say hello to your NerdHeads from me."
"Eh?" says I.
"NerdHeads, you know all those sad people who talk about tyre pressures."
"Tyre pressures, er, I don't know what you're talking about...."
LOL!
Very interesting post guys,
The general rule of thumb for front engined cars on trackdays is as per the first post - 10% additional pressure all round. This gives the tyre walls more support at low temps, creates less flexing and therefore less unwanted heat (friction) - furthermore on front engined cars on trackdays a normal roadcar does not have enough negative front camber to allow enough contact patch on cornering.
In a modified Audi RS4, an extra 5psi all round was lap for lap quicker at Croft on soft wall tyres - however on Mrs Lennon AVS's, which have a very stiff wall, the difference was not as noticeable.
Interestingly enough, with Derek Bell on an Audi Sport driving day, in an S4 Avant, on SP2000's he confirmed that these type of road cars are faster with more psi all round for the reasons above.
HOWEVER, rear engined Porsches must be different for the reasons you guys have mentioned, and it does make sense, especially as some of the 930/993/996 standard suspension specs I have seen run a lot more negative front camber than most normal road cars do,and therefore have better turn-in anyway.
Andiroo.
The general rule of thumb for front engined cars on trackdays is as per the first post - 10% additional pressure all round. This gives the tyre walls more support at low temps, creates less flexing and therefore less unwanted heat (friction) - furthermore on front engined cars on trackdays a normal roadcar does not have enough negative front camber to allow enough contact patch on cornering.
In a modified Audi RS4, an extra 5psi all round was lap for lap quicker at Croft on soft wall tyres - however on Mrs Lennon AVS's, which have a very stiff wall, the difference was not as noticeable.
Interestingly enough, with Derek Bell on an Audi Sport driving day, in an S4 Avant, on SP2000's he confirmed that these type of road cars are faster with more psi all round for the reasons above.
HOWEVER, rear engined Porsches must be different for the reasons you guys have mentioned, and it does make sense, especially as some of the 930/993/996 standard suspension specs I have seen run a lot more negative front camber than most normal road cars do,and therefore have better turn-in anyway.
Andiroo.
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