Tire Pressures

[Scott Farquharson]

The question i get asked the most at track days is "what tire pressures do you run?"  Pretty simple, pretty basic but it one of the things that can have a huge impact on lap times.

Maybe we could get everyone to put down what pressures they are using successfully for a particular car/tire combo.

[Evan Bottcher]

*bump*

I'm interested to hear what people have to say here as I've heard differing opinions.

I've just started running some old Dunlop D01J 195/60 14".  Haven't had a lot of time to play with pressures.  I was starting them a bit higher say 26-27lb cold to come up to about 32 hot, but at the 6 hour I had some advice from Andrew to aim for 28 pound hot all round.  I started them at 24 pound and they came up to about 29 pound, felt heaps better - holding on better through the esses particularly.  Thanks Andrew - that's my new starting point.

How do you tell whether to go higher or lower?  On road tyres I mostly used to bring down the pressures in the rear tyres because I could feel the rear sliding around, the R specs seem to just hold on regardless.  On road tyres I rarely was sure which way to go with the front pressures, unless I was way too high and the front was pushing in the tight corners more than normal. 

Any advice for a newbie?

[Sheldon McIntosh]

When I started out, (feels like years ago, but was only last year), I asked 10 people their opinion, and got about 30 different answers.

In general I found that very high pressures were needed on road tires.  I think I started on about 40!.  Was getting a bit of understeer so went down a couple of psi in the front.  Was going a bit faster, now getting a bit of oversteer, went down 1 psi at the back............

Race tires, a slightly different proposition.  Still have no idea what I'm doing on those.  They seem to change character all the time, and I'm still not sure what part of it is down to pressure, temperature of the air, just how knackered the tires are, etc.

But for the record, i'm running Kumho Ecsta's in a 205/45/r16.  Remember my car is quite heavy with standard springs.  I was told 34 is a good hot temperature, so I started with 30 front/28 rear.  Too much understeer, so went to 28 all round, much better.  Got terminal understeer after about 30 laps at 6 hr, tires were toast, but was able to drive around it after 30 laps.

Would be a very good thing to get a handle on though, very cheap and easy way to get speed if you can isolate just what effect tire pressures are having.  If anyone ever finds out, let us all know.

i remember when my dad was doing sprint days in his Porsche, he used to have a temperature gauge to measure outside/middle/inside of tire with different pressures after a run.  I never did find out the results.  I suggested to Bruno we should take one of those to a track day.  He looked at me with disgust.  "why, can't you tell what your tires are doing?"   

[shane wescott]

Haven't done any racing myself, but I did do a Jim Murcott driving course some years back where we were told to put 34 - 36 psi in road cars at all times.

I have done this ever since and while in some cases the ride seems harder, the grip has never been an issue, neither has wearing of the centre of the tyre.

Jim's theory came from his racing days and even a story of running 60 psi in an old falcon to make sure it hung on in a race.

Just my experience :-)

Catch ya

Shane

[Doug Gould]

Tyre placard pressure are a comprimise between fuel economy / ride comfort and performance. No one at OE level has much interest in life. It is decided jointly between the car company & tyre company and can get quite political. The tyre companies generally recommend that the full load or high speed pressure is used in all conditions for optimum grip.

On the track you are really looking to get the whole width of the tyre working. This is shown by the tyre tread being at the same temperature. A tyre probe is best because the core tyre temperature can be different from the temperature of the tread surface. The best theory is that tyre temperature is primarily built by the air compressing & expanding inside the tyre rather than from the tread / track interface. Most race engineers will say that the swerving under the safety car / in warm up laps does very little for tyre temperature. Braking, however, does a lot for brake temperature.

In my GTV6 on road tyres, I basically aim for 40 psi on all tyres hot. On a hot day, this may be at about normal cold pressure. The target pressure will depend on tyre profile and type (eg type R). My approach would be to start at not much more than the high speed placrd pressure and vary from there (maybe 2 psi less at the rear). Use hand feel to check for even temperature accross the tyre and observation of how much of the tyre edge is used to get the pressure right at the front and go up or down at the rear to trim the handling. The next day I usually find that all 4 tyres have different cold temperatures.

Getting the tyre pressures exactly right for the best lap times are the least problem for many of us. Concentrating on smooth lines is still the thing likely to show most benefit.

The stories about high pressures are usually from the old days and probably associated with cross ply tyres or high profile tyres that needed help to not "tuck under".

[Scott Farquharson]

Bump

any more track day tire pressure combos?

[Scott Farquharson]

*bump*

I'm interested to hear what people have to say here as I've heard differing opinions.

I've just started running some old Dunlop D01J 195/60 14".  Haven't had a lot of time to play with pressures.  I was starting them a bit higher say 26-27lb cold to come up to about 32 hot, but at the 6 hour I had some advice from Andrew to aim for 28 pound hot all round.  I started them at 24 pound and they came up to about 29 pound, felt heaps better - holding on better through the esses particularly.  Thanks Andrew - that's my new starting point.

How do you tell whether to go higher or lower?  On road tyres I mostly used to bring down the pressures in the rear tyres because I could feel the rear sliding around, the R specs seem to just hold on regardless.  On road tyres I rarely was sure which way to go with the front pressures, unless I was way too high and the front was pushing in the tight corners more than normal. 

Any advice for a newbie?

They should increase approx 6 pounds from cold to hot - probably start at 23 and see how you go - a good job for a sprint meeting.

A common mistake is to have too much cold pressure.

[Fast Eddie]

From memory, I think my starting pressure for D01j's on the sprint was 26 cold.
Brad does that sound right to you cos i would have told you to start on the same pressure.

[Brad M]

Yeah the plan has been for the Dunlop D01j's to start at 26 in the front and 28 in the back, these get up to about 32 which is optimal according to the maestro Bruno.

I have new Yokohama Advan's now that I'm starting the same way.

[Evan Bottcher]

these get up to about 32 which is optimal according to the maestro Bruno.

I know it's blasphemous but I'm going with Maestro Carra - 28 pounds hot all round felt fantastic at Winton at the 6 hour...

[Brad M]

Evan, Sounds like you want an arm wrestle to sort this out.

Mind you I couldn't get near you last time at Winton. What did you have in them cold to get to 28 hot? did you start at 22 cold?