What track tyre pressures for MPSCs on a 993

[tertius]

As per title - on 17" wheels.

For Bedford tomorrow.

cheers

[thegoose]

I try to race around the recommended hot pressure of 34-36 psi (PM me for exact figure, but I doubt you'll need it, given the rest of the post....) all round (starting about 8psi lower than my target on the left side of the car, 7 lower on the right). However, I heard different from a mechanic on another team, so tried dropping to well under 30 hot at Brands Hatch, using a significant drop for the sake of experiment/example. Lap times were virtually unchanged, but the tyres didn't overheat the same and go off after a long hard session. My conclusion is that it doesn't make much difference (someone else had told me this already) but that for circuits with longer fast sections I will run higher pressures as there is more chance of the tyres cooling down a bit bewteen bends and the reduced drag is an advantage.

[Agent Orange]

These tyres were built to be best at 36 hot all round, original Michelin literature ..............toyo 888 are half the price and almost as good ,sorry!

[thegoose]

Agent Orange said:

These tyres were built to be best at 36 hot all round, original Michelin literature ..............toyo 888 are half the price and almost as good ,sorry!

No need to apologise, I agree. PSCs are the control tyre for the Porsche Club Championship so I have to use them. The OP seems to already have them, hence I gave the advice he asked for. I drove a friend's 3.2 (track set-up including different gear ratios) round Paul Ricard on R888s and thought they were fantastic, knowing they cost a lot less. Not sure which would offer the most outright grip (i.e. best lap time) in a back to back test, but pound for pound better value.

[tertius]

thegoose said:

Agent Orange said:

These tyres were built to be best at 36 hot all round, original Michelin literature ..............toyo 888 are half the price and almost as good ,sorry!

No need to apologise, I agree. PSCs are the control tyre for the Porsche Club Championship so I have to use them. The OP seems to already have them, hence I gave the advice he asked for. I drove a friend's 3.2 (track set-up including different gear ratios) round Paul Ricard on R888s and thought they were fantastic, knowing they cost a lot less. Not sure which would offer the most outright grip (i.e. best lap time) in a back to back test, but pound for pound better value.

That's OK, I got two very cheaply, so only paid for two really. Otherwise I would probably have gone for Toyos, I'll go for those next I expect.

Thanks for the advice on pressures.

[Agent Orange]

i have used both and unless ur Jackie Stewart watever, i dont believe on a dry track there s a second a lap in it for most places, without rubbing it in u start with more tread on the Toyos , unles u have hand cut MSPC , not road leagl of course, the toyos far superior in wet and finally dont seem to go hard with heat cycles quite so fast ............i am far too old to race and for track days its a no brainer ...........i rEst my case M'LUD !

[zub]

On 18 inch wheels on the RS and Cup car in the dry I run 32-33psi, slightly lower than Vic's 36psi. If it is wet, put them up a bit (36-38), with more at the front. From cold start at around 26-28 and keep dropping the pressures every time you come to the pits as the tyres warm up.

Have fun!

Z

Edited by zub on Thursday 23 August 22:29

[johnny senna]

Agent Orange said:

i have used both and unless ur Jackie Stewart watever, i dont believe on a dry track there s a second a lap in it for most places, without rubbing it in u start with more tread on the Toyos , unles u have hand cut MSPC , not road leagl of course, the toyos far superior in wet and finally dont seem to go hard with heat cycles quite so fast ............i am far too old to race and for track days its a no brainer ...........i rEst my case M'LUD !

Hi Vic. Any idea what sizes the Toyos come in? I'll have a look on google actually......one minute.

[johnny senna]

Reet, I'm back. They have all the right sizes. Where's the best place to order them from? Anyone know? Sorry for the thread highjack!!!!!!!!

...........just found a set of 4 Toyos for my car for £690. Sound about right?

Edited by johnny senna on Thursday 23 August 22:48

[sleep envy]

Agent Orange said:

These tyres were built to be best at 36 hot all round, original Michelin literature ..............toyo 888 are half the price and almost as good ,sorry!

you sure that's not just for 18"?

IIRC the PSI for 17" is different for front & back

[flemke]

thegoose said:

I try to race around the recommended hot pressure of 34-36 psi (PM me for exact figure, but I doubt you'll need it, given the rest of the post....) all round (starting about 8psi lower than my target on the left side of the car, 7 lower on the right). However, I heard different from a mechanic on another team, so tried dropping to well under 30 hot at Brands Hatch, using a significant drop for the sake of experiment/example. Lap times were virtually unchanged, but the tyres didn't overheat the same and go off after a long hard session. My conclusion is that it doesn't make much difference (someone else had told me this already) but that for circuits with longer fast sections I will run higher pressures as there is more chance of the tyres cooling down a bit bewteen bends and the reduced drag is an advantage.

Fwiw, I wouldn't drive with abnormally-low pressures and rely on working the tyre to bring them up to the correct level.
Any time you spend driving with too-low pressures - especially if you're loading up the tyre - will distort the contact patch and can damage the carcase.

Best to do one or two laps starting with cold pressures the same as either your target hot pressures or your normal road pressures. After the tyres are warm, let them down to the hot target. Repeat the process a second time, and a third if necessary.
It's a pain in the neck, and damn inconvenient at a track day when there may be long breaks that allow the pressures to drop, but at least start the day by taking precautions.

[Agent Orange]

on the MSPC i have run lower pressures on a fairly powerful rear engined car..........trying to experiment with even temp across the tread the 36 psi actually worked well with really even temp and wera the result..........but then ur into cambers, so like for like is neccessary. I have nt used the MSPC for some time now run track days with 100 bhp less ,on toyos with cambers i have, i am using 30 front 32 rear hot no untoward 'edging' though i gather the GT3 guys need higher pressures.......my car however is lighter ..............its all fun!!But the Toyos are cheaper
Doc ur man is Steve Girdwood Simply Tyres , cheap and friendly will drop em at Andy s watever u ask ..........ps Andy knows him well.

[johnny senna]

Thanks Vic.

[thegoose]

flemke said:

thegoose said:

I try to race around the recommended hot pressure of 34-36 psi (PM me for exact figure, but I doubt you'll need it, given the rest of the post....) all round (starting about 8psi lower than my target on the left side of the car, 7 lower on the right). However, I heard different from a mechanic on another team, so tried dropping to well under 30 hot at Brands Hatch, using a significant drop for the sake of experiment/example. Lap times were virtually unchanged, but the tyres didn't overheat the same and go off after a long hard session. My conclusion is that it doesn't make much difference (someone else had told me this already) but that for circuits with longer fast sections I will run higher pressures as there is more chance of the tyres cooling down a bit bewteen bends and the reduced drag is an advantage.

Fwiw, I wouldn't drive with abnormally-low pressures and rely on working the tyre to bring them up to the correct level.
Any time you spend driving with too-low pressures - especially if you're loading up the tyre - will distort the contact patch and can damage the carcase.

Best to do one or two laps starting with cold pressures the same as either your target hot pressures or your normal road pressures. After the tyres are warm, let them down to the hot target. Repeat the process a second time, and a third if necessary.
It's a pain in the neck, and damn inconvenient at a track day when there may be long breaks that allow the pressures to drop, but at least start the day by taking precautions.

I only started racing 2 years ago so admit I don't have the most experience at this, but the settings used were arrived at by setting hot pressures, then seeing what they were when cold (usually the next day). We then used these as starting cold pressures and the hot pressure when checked was usually correct, or close to it. Given that the cold pressures I have been working to are only marginally below what a technician from another Porsche team said they use as hot pressures, I don't think I am driving with the "too-low" pressure you suggest. The car is not used on the road (except on trade plates to run in engines/gearboxes etc) and there isn't the opportunity to stop and adjust pressures when racing, so we have to start with the cold pressures we believe will give the correct hot pressure once up to temperature. I do tend to try to get them up to temperature (for the adhesion properties as well as pressure) as quickly as possible. Most drivers seem to just weave around the circuit on the greenflag lap, whereas in addition I will get a little understeer, then add another half-turn or so of lock, thereby inducing greater friction and hence temperature. I will induce power slides too for the same reason. It seems to work OK as I'm usually one of the best starters on the grid (although some are front engined admittedly).