Geoff M

Any hints on tyre pressures? I've been running mid 40 psi on the fronts and 5 to 6 psi less in the rears. I've got Koni adjustable dampers and 30mm lower, progressive rate springs, and an anti-lift kit, and -1 degree camber on the front, but I still can't stop the understeer. It's not terminal, just frustrating having to wait until I'm almost out of the corner before I can get much power on.

Darren Soothill

The tyre pressures sound rather high. I presume you have some details of the spring rates that are fitted to the car and what position you have the various damper settings set to.

What are is the rest of the steering geometry set to ?

Have you spoken to Koni to see what they suggest?

It sounds like the spring rates are a bit out of balance. Increasing the rear spring rate and reducing the front spring rate may help.


Darren




[This message has been edited by Darren Soothill (edited 29-06-99).]

MarkL

You're probably reducing your grip levels by a fair amount by running such high tyre pressures. I run slightly over-inflated at around 35psi fronts and 32-33psi rears to sharpen up the handling a bit without loosing too much grip.

WESTFIELD

You probably need high pressures to prevent excessive tyre wear with heavy track use.

You could try increasing the rear roll stiffness (thicker roll bar, uprated links and bushes etc.) to enduce the rear end to slide a bit more.

Lee

whoah far too much pressure. When my dealer delivered mine with 40psi all round I thought the handling was naff..till I lowered it to 33/30.

SimonLogan

I totally agree Lee,
(there must be 50 ways.. )
mine came with 40 psi and I had terrible understeer in the wet. I have mine at 33/33 and it is a big improvement. Do you find 30 at the back causes the back to slide more easily? (hope so!).

Simon

Andy Tang

iTrader: (3)

I was running my car with 40 psi, and the understeer was appalling. I have recently changed to 33/30 setup, and have noticed that I'm getting a very progressive oversteer when pushing the car hard.

Hope this helps
Andy

ColinU

When folks are refering to tyre pressures (say 33/30) are they measuring this hot (after driving for a while) or cold (e.g. first thing in the morning)?

If I measure my tyre pressure from cold then drive sedately 1 mile down the road the pressure increases by 1.5 to 2 psi. I've always been led to believe the 33/30psi should be measure cold.

Comments?

david

On my MY98 I used to run 33/27 (like the book tells you) and found this to provide excellent handling in all conditions. I've recently changed to an STi V, is the rear pressure still OK with the extra performance?

Geoff M

Thanks for al the response guys. I have since left my pressures at 35/28 (2 up on standard at the front and 2 down on standard at the rear) for fast work and find the handling is much better. The anti lift kit helped a lot in the tighter stuff.

I found some tyre company and racing club web sites which pretty much concur with these suggestions. Only vary from standard by 2 or 3 psi (measured cold). If that does not move thehandling bias as required, then suspension needs to be modified.

I'm from Australia BTW and would be pleased to answer any questions about conditions, cars, roads etc. I've spent some time in UK, so might be able to offer comparisons.

My local WRX Club site is at www.wrx.com.au if you are interested. Nothing like this site - compliments to the webmaster and members for contributing.

AndyG

Geoff, I'm interested in why you have the fronts so much higher than the rears. Is this an effort to get rid of understeer? Does it work?

Andy

Geoff M

Yes, I am trying to move the bias more towards oversteer, which is what I am more comfortable with, being an old rear wheel drive rally exponent.

The standard difference front to back is to compensate for weight distribution. I jus ttry to move it a little bit more.

I was out on the weekend having a play, and found that 35/28 works a treat.

Fred

Hello guys,

Does the pressure around 35/30 psi can be apply to a 215/40/17 tyres ? with bilstein stiff suspension ?

I'm always running with higher tyres pressure (38 /35 psi) because the tyres are always reaching the end of life on the exterior and interior side...

It is the same thing for you ?

Richard F

David,

I'm running an STi V as well and have found that 27 on the rears is a bit low for my taste. I run at 34 all round because I prefer the slightly firmer almost nervous (only almost!) feel it gives. With the rears at 27, it seems harder to control it smoothly on the throttle.

SimonLogan

Guys,

according to the thread which was started by mike nunan (I believe), lower pressure gives more grip. This implies that you want to raise the rear pressure to increase oversteer. Has anyone experimented with this?
Also, has anyone fitted rear ant roll bar bush supplied by the australian rally company (can't remember their name, but they seem to be the authors of the impreza FAQ). Did this increase oversteer?

Simon