track tyre pressures

[red997]

Hi Guys
Got my first track day coming up in a couple of weeks time in my newly aquired 997 C2S.
What's the general concencus on cold tyre pressures for track use, and oil level ?
Tracked a 986S & a 996 C2 before, but not the 997.
Tyres are 295 30 19 & 235 35 19 Pirelli Pzer rosso, if it makes any difference.
Thanks
David

[GuyS.]

Hi David,

Although I use Toyo's now I used to run Pirelli's and suggest 35 psi front and 39 rear cold.

Check the pressures every time you come in and keep bleeding them down to that level. Don't be surprised if you let a lot of air out as the tyres get hot ( about 10 psi over 3 bleeds is about usual for me). After a while the tyre pressures will stabilise.
Try and remember how much you have bled out so you can put it back in before you drive home otherwise the pressures will get too low as they cool.

Regarding oil levels 3/4 to full.

Have a great day.

[red997]

cheers for that - track temp this time of year shouldn't be too high, so may not need to bleed as much out as I think.
David

[batman69]

track temp won't drive tyre pressures as much as other factors, it will be how much heat you generate in the tyres due to acceleration, braking and cornering. You should be needing to bleed air out as the tyres heat up.

[andmole]

When I used to compete in sprints and hillclimbs,(VERY modified MG midget), myself, and all the other guys in my class, used to run higher tyre pressures in the FRONT tyres. The theory behind this was, (from a guy who knew a lot more than I did), that a lot of understeer is caused by the front tryes trying to roll off the wheels at high cornering speeds, due to the high lateral forces. So I used to have 2-4 PSI more in the fronts than the rears. Of course it would depend on the car and its usual set up, but basically my advice would be not to drop the pressure in the front tyres too low. If you get more understeer than you expect, try putting a bit in.

[red997]

this backs up the 'theory' that I've been told about, primarily by Brit car & Touring car teams.
However, they were not in Porsches;
Everyone seems to be on the side of lowering the pressure for track use on a 997. This is kind of why I asked the question !

Common sense says that if the pressures raise significantly during track use, then air should be let out to compensate.
But the question is how much. Porsche cold pressures are just that - cold. After a bit of spirited road use, they will naturally go up.
But to what pressure - who actually measures them - do you then reduce them for road use ?
I can understand tweaking the pressure balance front to rear to counter in / out understeer.
So, I'm still in a bit of a quandry !
David

[paulburrell]

As Guy said, it's all a bit of trial and error. If tyres are nicely warm and gripping well at 35/39 after bleeding then leave them at that. If you are encountering problems at that pressure and temperature then lower them in 1 psi increments. If handling trait is getting worse rather than better then you may need to go the other way and raise them above the 35/39 combination. You will need a good pressure gauge though, not the bog standard Porsche jobby. Best solution is to dump the Pirelli's(or buy a spare set of wheels)buy a set of Toyo R888's(not sure if they do 19" wheels tho) drop them to 34/38 hot and prepare to hold on for grim death. Enjoy!!!!!

Edited by paulburrell on Friday 1st December 09:10

[smckeown]

GuyS. said:

Hi David,

Although I use Toyo's now I used to run Pirelli's and suggest 35 psi front and 39 rear cold.

Normally the driven wheels heat up more, so generally the cold temp pressure is lower

[sdd]

Yes but he's in a 911 where the rear pressures are naturally quite a bit higher than the front because someone lobbed an engine over the back of the axle. Just make sure you check them and bleed back to your chosen starting point. There will be other 911's on track, speak to a couple of them to see what they have found to work best.

[iguana]

Ask on the pork forum, lots of trackdayers there. In general tho folks do run 911s with much too high rear pressure & wonder why its all over the place, the track regulars run lower than you may think- altho tyre presures much like car set up in general is a personal thing so what suits one maynt suit another etc etc.

[red997]

an after the event report;
OPC said RAISE tyre pressures;
On site tyre specialists said keep as std road, then adjust to desired car response;
I went with std road high pressure - came off after 6 or so laps, and found that 44 had risen to 52 psi !
droppped 2 then another 2 out of the rears; all OK;
Car was then understeering slightly, so dropped 1 from fronts - nice & neutral again
Excellent day - I was VERY impressed with Bedford Aerodrome & the organisation of Palmer motorsport - definetely go there again - and the instruction was top notch.

The car surpassed my expectations !

David

[smckeown]

red997 said:

an after the event report;
OPC said RAISE tyre pressures;
On site tyre specialists said keep as std road, then adjust to desired car response;

What a bunch of amateurs, it's obvious the tyres will get hotter on the track than on the road. I normally drop 4psi over what I run on the road. But checking the pressures hot when coming into the pit is the only way to monitor the true pressures.

Sean

[smhmotorsport]

red997 said:

an after the event report;
OPC said RAISE tyre pressures;
On site tyre specialists said keep as std road, then adjust to desired car response;
I went with std road high pressure - came off after 6 or so laps, and found that 44 had risen to 52 psi !
droppped 2 then another 2 out of the rears; all OK;
Car was then understeering slightly, so dropped 1 from fronts - nice & neutral again
Excellent day - I was VERY impressed with Bedford Aerodrome & the organisation of Palmer motorsport - definetely go there again - and the instruction was top notch.

The car surpassed my expectations !

David

Dont totally agree with changing the tyre pressures, sounds like its to compensate for set-up. The tyres will work best at their optimum pressure, once found leave them. Let the tyres cool then check the pressures again. This will give you a cold pressure to start with, and when you go out the next time after a few laps the tyres will be back to pressure. I dont have any experience on Porches, some mates have, but I wouldnt expect the track tyre temps to be too different from road. Some race drivers play with their tyre pressures when whats needed is a better set-up on the car. Fix the fault, not cure the problem.

[Ian964]

On track, a 911 rear tyre pressures will go up by 8-10psi, fronts by about 5. In a 964, I start with 36 cold all round - after a few laps these will be 45 rear and 41 front. The back starts getting very twitchy - dropping them all back to about 38 hot seems to cure this and make the car much more stable again.

Take a tyre pressure guage along, check the pressures all round immediately after a few laps, and let some air out if necessary. Make sure you have your air pump with you, as at the end of the day you should let the tyres cool then pump them back up before going home - there have been a few reported rear tyre failures where they haven't been re-inflated (mainly on GT3s with MPSCs)

[semprini27]

For a first trackday leave the pressures at standard (COLD) pressures and concentrate on learning how the car behaves. A 911 is different to most other cars and you will have enough to learn about without worrying about tyre pressures.

The majority of offs I've seen from 911s on track days come from a fundamental misunderstanding of the physics of the car and how it will behave under braking / turn in / acceleration. That and over-ambition under braking !!

Enjoy !!

[red997]

Hi All
Just like to point out that this was not my first time on track in a 911; only the first time on track in my new 997 version.

I'm well aware of the driving dynamics of a 911...!

although, the 997 is the best behaved I've ever driven.

I did stick with std pressures, and then monitored them after every session (approx 5 laps of the GTcircuit)
The track was dry all day, air temps about 9 deg C.
So, tyre temps were fairly high, as I was using all the available grip (braking from 140 at the end of the straight got heat into them really quickly !!)

The tread was very sticky after a few sessions - so much so, I could pick out chunks of rubber ! now I know why so many of the cars, especially the GT3's, had track orientated tyres...the Toyo trade van was doing roaring business.

I think more track time is always a good idea - though I did use 2 tanks of fuel during the day on track alone (which at 9mpg equates to 230 miles, or 65 laps !!)

Looking forward to the next track day now - although when these tyres are worn out, I will be seriously considering some track focused tyres.

David