19/10/2004 18:11:11 JP12 Does anyone know what the optimum tyre pressure is once at track temp? Simply going by the wear patterns on my tyres I have found that when at track temp 35psi seems to be about the best pressure for my Clio. To get 35psi when hot I need to set the fronts at 31psi when cold with the rears slightly higher. I have only done this over a couple of track days and have really just be guessing by the wear characteristics on the tyre. I know this will vary due to tyre profile and sidewall stiffness, but I was wondering if anyone had anymore technical info instead of my rough guestimates. I haven't managed to do this for my MGB as I have yet to get enough track time to experiment before it stops:mad: Plus, if I increase the tyre temps when cold as lots of people advise I end up with close to 40psi when hot!! The tyres don't wear so bad but it handles like poo! I was also advised to decrease my tyre pressures in wet conditions. I experimented with this at Castle Combe and found I lost grip by decreasing the pressure. I spoke to David Da Costa who is apparently a very experienced instructor and he advised me to increase the pressure. WOW! It totally changed the car, I will stick to increasing the pressure from now on when wet. So does anyone have anymore info? Joe

19/10/2004 23:09:28 Paul Nothard I aim for 31psi all round when the tyres are hot. That works well for me on 195/55R15 tyres. Have experimented quite a bit and higher pressure makes the car slippy. Lower pressure 'grips' a little more but is more wooley - with bad tyre wear too! In the wet... well, I just wing it really. :) Haven't the experience. P.

20/10/2004 07:32:19 Neil Everyone told me to increase pressure when I went on the first trackday and it was like driving on ice. Now I use 28psi cold which appears to be about 31-32psi hot appears to provide the right amount of grip.

20/10/2004 08:51:38 Paul Nothard [QUOTE=Neil]Everyone told me to increase pressure when I went on the first trackday and it was like driving on ice. Now I use 28psi cold which appears to be about 31-32psi hot appears to provide the right amount of grip.[/QUOTE] The "increase the pressure" theory is most probably from the days of "high profile" tyres where the extra pressure stiffened the tyre wall. The best thing about advice is that you can ignore it. :) P.

20/10/2004 10:45:54 Rob Bell Just to muddy the waters a little more - I suspect that the tyre pressure that you use will depend hugely on the kind of circuit you are driving, and the ambient temperatures. To my mind (and I think we're all in consensus here), it is the pressure that the tyres reach when hot that is critical. At places like Donny, I actually drop the tyre pressure (about 28psi, like Neil). But at others, I may stay at 30. If it is cold/wet, then the pressures in the tyres never reach the same level as they would on a warm, dry day - so for this reason, increasing the 'cold' pressures starts to make sense (and I've done this before with some success). The other variable is the tyre itself. Some tyres simply have rather flexible sidewalls, whilst others (eg the Bridgestone S-02/03) the side walls are very stiff. The more flexible the tyre, mthe more sensitive it is to tyre pressure. A classic has been the Toyo T-1S. Needs a lot of pressure in the side wall to prevent them from keeling over. I used to find something similar with the Goodyear F1 GS-D2. The GS-D3, the replacement F1 tyre, has a much stiffer tyre wall, and I am finding that I am using 2psi less pressure now than I was then... I am sure that a quick google search will throw up lots of technical sites that go into this 'black art' in much more detail - but I think that it ends up being a 'suck it and see'... :rolleyes:

20/10/2004 14:01:27 Paul Nothard [QUOTE=Rob Bell] I am sure that a quick google search will throw up lots of technical sites that go into this 'black art' in much more detail - but I think that it ends up being a 'suck it and see'... :rolleyes:[/QUOTE] Shouldn't that be blow it and see - if you'll pardon the phrase. ;-)

20/10/2004 14:52:09 Rob Bell [b]Shouldn't that be blow it and see - if you'll pardon the phrase. ;-)[/b] Oo-er missus!!! Maybe depends on whether you are increasing or reducing tyre pressures? ;) :D

20/10/2004 19:33:59 JP12 Looks like I am on the right track then. I will keep experimenting and see what is best for me. Joe

20/10/2004 21:26:13 NickPS As Rob said, it will surely depend on the car and size of wheel and tyre too? I use between 30psi and 35psi on my MGB depending on the circuit and temperature. Another thought for discussion - Donington 2004 was my first track day on lowered and stiffer suspension. I noticed a significant reduction in tyre wear and they were much cooler after each run, even though the car is much quicker... I guess this is due to a massive reduction in understeer (it was terrible on the standard set up and had to be flicked into corners with big oversteer, karting style, to get round!) and the fact that all four wheels spent more time on the ground as I usually lifted the inside rear on fast or tight corners. Any other thoughts? Regards, Nick

21/10/2004 08:43:24 Rob Bell Now that is very interesting Nick - clearly your suspension is working so much better now! :D Exceeding the slip angles so frequently with under and oversteer is bound to generate more heat - and I would imagine that driving style will have a significant impact too...?

24/10/2004 15:22:10 v8dave Guys, When you quote tyre pressures please remember to say what tyre you use as well as what the car is. I ran 20 psi in the fronts and 22 psi in the rear at Donnington - useless unless you also know that the tyres are yokohama A048R 195/60R14 and I was using them on a B GT V8 with lowered suspension and uprated brakes. I suspect the traditional advice to raise your pressures on track is less relevant today than it was 20 years ago, tyre construction has changed and suspension on modern cars should be much better. The best advice I can offer is read your owners handbook to see if there is any advice - if there is start with that and experiment. Remember - what works for me might not suit your car or your driving. Dave

10/11/2004 19:08:41 don k When having new BF Goodrich G-Force Profiller tyres fitted for £2.50 per tyre they fill them with Nitrogen in place of air. Temp changes does not effect the pressure so much Plus no damp air to corode your alloys. These tyres i ran at 28F and 30R with no problems at Pembury, excellent in the wet and cheap too don

20/01/2005 13:42:54 Woodhouse Racing Hi, Its got as much to do with temperature as it has with pressure, check out this article on : [url="http://pub29.bravenet.com/forum/2440548016/show/414631"]http://pub29.bravenet.com/forum/2440548016/show/414631[/url] its a good read, and applies to all cars on any track Laters

20/01/2005 14:24:00 Dave [QUOTE=Woodhouse Racing]Hi, Its got as much to do with temperature as it has with pressure, check out this article on : [url="http://pub29.bravenet.com/forum/2440548016/show/414631"]http://pub29.bravenet.com/forum/2440548016/show/414631[/url] its a good read, and applies to all cars on any track Laters[/QUOTE] That's an interesting approach - presumably there is no reason why it wouldn't work on road tyres as well as slicks?

20/01/2005 15:55:41 Woodhouse Racing They all work on the same princaple, + you not only set up the tyre pressure's but the tracking and the camber too......

20/01/2005 17:31:19 Rob Bell So who's going to buy a pyrometer? Looks as though the reduced price of 30 quid holds to the end of this month... :)

20/01/2005 17:48:56 Dave [QUOTE=Rob Bell]So who's going to buy a pyrometer? Looks as though the reduced price of 30 quid holds to the end of this month... :)[/QUOTE] Just ordered one Rob :) Another test to do at Brands ;) assuming they get them in stock in time - currently says 28 days. :(

20/01/2005 17:56:13 Rob Bell LOL - nice one Dave! I want to play with it as well, assuming that it arrives in time? :D Hmm - could also come in useful for that water pump project we've had on the simmer all this time? ;)

20/01/2005 18:25:41 Dave [QUOTE=Rob Bell]LOL - nice one Dave! I want to play with it as well, assuming that it arrives in time? :D Hmm - could also come in useful for that water pump project we've had on the simmer all this time? ;)[/QUOTE] Yep - that's what I thought :D

21/01/2005 14:45:32 AndyB [b]Pyrometer[/b] [QUOTE=Rob Bell]So who's going to buy a pyrometer? Looks as though the reduced price of 30 quid holds to the end of this month... :)[/QUOTE] I've got a laser temp gun, which I'll be bringing to Brands. It's best to take the readings as soon as poss after your session, which means having a mate (or someone from a different session!) ready with notepad and gun as you pull in. Maybe we can organise a temp taking checkpoint and really get some data! Andy

21/01/2005 16:15:22 Rob Bell That sounds like a very good idea Andy! :)