911

Been practicing at Prescott hill climb today, racing tomorrow.
I normally race my V3 with 16 x 50 x 205 Kumho v70's soft compound tyres at 33 psi allround.
After a discussion in the paddock/class the EVO 5 runs 40psi! The Nissan GTi 20psi (exact same tyres) and me at 33 psi
Tried a run at 30 psi and all was good, tried 27 psi and things were looser.

Anyone tried anything like this and have any comments?

Going to race on 27 psi tomorrow

Graham.

superstring

This will be very interesting, Graham. Keep us posted.

I don't race my car, but I've experimented quite a bit with tire pressures on the road and I find changing the pressures just a little makes a big difference in the way the car rides/handles.

Cheers.

dazc

I have mine a couple of psi over for road use as it seems to make it more direct, although you can feel the bumps more. Any less and it feels too sloppy for me, any harder and it's not nice in the wet.

On trackdays you generally run tyres at 5psi over recommended pressure, (approx manufacturers max load/sustained high speed) which would be something like 38 and 36 to reduce sidewall flex. Also lap after lap would increase the pressure due to heat build up, which you wont have as much of. I would try somewhere between 38-40 as the evo. 20's seems a bit low imo.

Daz

PS. Who's the fastest, you, Datsun or Evo?

911

After the 3rd runs today:

EVO @ 47.3 secs 450 bhp
Sti @ 48.36 secs at 400 bhp
Nissan @ 49.6 at 320 bhp ish (he never tells you anything)

All a bit close...

Graham.

Floyd

iTrader: (9)

I run mine at 45 on track. I thought you were going to try 37?

F

dazc

Assuming the course is twisty where power isn't everything, that would be:

EVO @ 47.3 secs 450 bhp 40 psi = fastest
Sti @ 48.36 secs at 400 bhp 30? psi = mediumist?
Nissan @ 49.6 at 320 bhp ish 20 psi = slowest

Is that over simplifying things?

Also if the Datsun driver never tells you anything, do you think he's really running at 20psi?

Daz

911

Right on running order so far!
Saw his pressure gauge which started the whole thing off.
I've done a '48' last meeting on 33 psi!

Bloody motorsport!

Graham.

911

What a fast day.
Came second in class at 48.09, oh so close to a '47' Ran 27 psi all day
Lost to the EVO who ran 46.7....There is just so much on that car! (and he is a good driver)

Thinking of going lower still, maybe 25's..

6 weeks till the next Championship round.

Time for a rest and a good think.

Graham.

Pavlo

I have found that the pressure is dictated by tarmac type. A course, open, natually ungrippy surface benefits from the lower pressures to help heat the tyre (due to flex and compliance). As soon as you get onto a very smooth surface, the high pressures work best. Usually the surface will be one of the two, and being in the middle WRT pressures is the worst place to be.

Paul

911

Floyd:

will try the '37' trick next meeting, which is in 2 months time(!)
On practice day I only get 3 runs, sometimes 2, so not much chance to try too many things.
27 gave great results today, the EVO runs 42 in the front...
Will try the 37 route on the road first.

Pavlo:

Agree, a hill climb surface is a good country lane, but smooth and no pot holes.
Crude as that.

Graham.

John 37

There is nothing to say you have to run the same pressures front and rear.

Varying tyre pressures is an easy way yo adjust the handing characteristics of a car. I used to rally FWD running 30/18 F/R. It made the rear a bit looser so meant I could apply power earlier in a bend without inducing understeer.
Prescott has some seriously tight hairpins so early power out of slow corners is essential for a good time. Try running the rears lower.

John