Another old chestnut - tyre pressures

[Eldavo]

So we've already had the good old chestnuts of "what oil" and "are 944s proper Porsches" - I'm not going to ask about the trip reset but rather, tyre pressures.

The filler cap sticker suggests 36psi front and rear but I usually run 32F and 34R cold and the same hot when on track.

I've just had Federal 595 RS-R trackday tyres fitted all round and was thinking about sticking with my standard pressures on the road but going up to 34F and 36R hot pressures on the track to stiffen the sidewalls a bit.

I know the answer is subjective and I should experiment on the day with different pressures but being honest I don't think I'd notice the difference from a few psi either way - I just don't want massively uneven wear across the tyre either on track or on the road.

Any advice from any of our resident track hooligans (probably pertinent to others "pre-Bedford" too)?

 

[944 man]

Id probably start with equal pressures all round.

 

[Eldavo]

0 psi all round is equal

 

[Riverside]

On the road I use 37psi all round, on a wet trackday I leave them at that. On a warm dry day I'd start at 32 all round, on a cooler day 34.

At Bedford I've generally found the fronts get warm first, then the rears a lap or so later, and a couple of laps later the fronts start to lose a little grip but by then the brakes & oil are all pretty hot too (lots of long straights & heavy braking into slow corners).

I have a few in-car vids from Bedford on youtube:
https://www.youtube.com/watch?v=nevzlmp87J4

 

[Lancerlot]

Pop into Aldi, buy yourself an infra red temp gauge for £17 and use it at the track to monitor tyre temps.

Take readings at the outer, inner edges and middle section of each tyre. You're looking for even temps across all sections of the tyre. Too hot in the middle = over inflation, too cool = under inflation.

Regards,

Clive.

 

[zcacogp]

For road use, I use the rule of thumb of looking at the maximum pressure as listed on the side of the tyre and knocking 10% off. Tyre manufacturers know more about tyres than car manufacturers and max-minus-10% seems to give a very good starting point for almost all sizes of tyre.


Oli.

 

[edh]

Dave

I think you'd be surprised how much difference a few psi makes to the handling on track & how it alters the balance. It's easy to experiment as well.

You're in the right area I'd say - maybe start 34/34 hot and see how it goes. See if there's any evidence of the tyre rolling onto the sidewall. Couple of psi lower in the wet.

 

[steve 944t]

I run 36 all round on the road and find that pretty good. On track I leave them at 36 cold, which generally has them at about 40 to 41 when up to temp. That said, I am on Toyo T1-Rs which have a soft sidewall and they do need to be run at high pressure on track to avoid the tyre trying to roll off the rim. Similar to Riverside, I tend to find that the brakes and oil are starting to overheat before the tyres anyway.

 

[Eldavo]

ORIGINAL: edh

Dave

I think you'd be surprised how much difference a few psi makes to the handling on track & how it alters the balance. It's easy to experiment as well.

You're in the right area I'd say - maybe start 34/34 hot and see how it goes. See if there's any evidence of the tyre rolling onto the sidewall. Couple of psi lower in the wet.

Thanks Ed, lower in the wet so they move around a bit more to heat up?

I'll try upping the front a little on road and see how it feels - I think a bit of general research on how the Federals work on track might be needed too!

I'm hoping that MarkK will chip in too.

 

[944 man]

Sorry Dave, I thought that youd know what I meant. Equal 34psi all round for a start, after that its down to you.

 

[944Turbo]

33 all round for me, lowered on track to 33 hot

 

[Cater_Racer]

I've usually started cold around 26 and aimed at 30 all round hot, with Toyo R888's and found it was wearing the centres out before the edge.

Maybe if I started with them a bit harder they would not get so hot??