Adam M

Simple,

want some ecommendations

WRX. 17 inch OZ super Ts, 215 40 17 Toyo proxes. Prodrive geometry .Pressure suggestions please,

GaryC

I also run on 17" OZs but with S02s - I run at 36 front and rear. Have played upto 4psi above and below, and 36 gives best compromise between ride, wet handling and dry handling.

GaryC

John - I'm confused - how does reducing rear tyre pressure by 2psi affect understeer? Surely only front tyre pressure will affect understeer????

DocJock

17s with SO2's. Normally 36 all round in wet. For fun in dry 36/34 for less understeer.

John

DavidRB

UK MY00 (standard suspension), 17" Speedline 7s, Pirelli P Zeroes. I run 32psi all round.

Have tried the high-front, soft-rear combinations that some people favour, but IMHO, it made the car understeer. As Mr H alludes to, maybe 16" tyres work better with different pressures front/rear.

Don't forget driving style also comes into the equation.

Lars

GarryC, try to do a Search on tyre pressure.
There was a large debat on this subject 1 or 2 months ago.
And John is right, lower pressure in rear tyres, will reduce your understeer.
You will not get more grip on the front, but less on the rear and that will improve the "turn in"
Regards Lars

MorayMackenzie

I think what Lars was trying to say was that increasing the rear tyre pressure whilst leaving the fronts alone will reduce the tyre contact patch, hence diminishing rear grip and increasing the cars tendency to oversteer.

Dropping the rear pressure will increase the contact patch, improve rear grip and reduce the tendancy to oversteer.

Increasing the front pressures will reduce grip and increase the tendancy to understeer... Reduce front pressure and it will grip better, hence reducing understeer.

So, in theory (don't try this at home!), 45psi front, 28psi rear will understeer like the Titanic and 28psi front, 40psi rear will feel distinctly loose at the back, a little like a RWD!

Moray

AndyMc

Moray and Lars

You seem to be saying different things(apologies if I have mis-understood)

Lars appears to be saying that lower pressure on the rear will reduce rear grip.

Moray seems to be saying that increasing pressure on the rear will reduce the rear grip.

I think both the above statments could be true and will try to explain my thoughts

I think that if you started off with very low pressures and then started to increase them grip would increase up until a point was reached where grip is at a maximum further increases in pressure would then result in a loss of grip.

This would mean that both increasing and decreasing the pressure could have the same results depending on wether the starting pressure was above or below this optimum and may explain why this is such a commonly debated topic.

I'm sure I could have explained this better but hopefully you can understand what I am trying to say

Andy

Diablo

Moray,

Can't agree with you on this one - its not as simple as that.

Within normal operating limits and for road tyres, higher pressures will promote more rigid carcas and sidewall and hence less understeer due to tyrewall and contact patch deformation when cornering.

In extremis, try cornering with fronts set at 10 psi and then 40 psi. Doesn't take much to work out which will give more understeer.

Agreed that over inflated tyres will have noticably less grip (say 45psi+), but within normal operating ranges, lower pressure = less grip (unless the point of maximum grip referred to above has been exceeded).

Lowering the rears would not reduce understeer at a given speed, but may improve front/rear balance of the car.

D.

[This message has been edited by Diablo (edited 13-04-2000).]

MorayMackenzie

D,

This assumes standard 16" subaru wheels and standard tyre pressure (32psi front).

That's an extremely biased example! You suggest 22psi less than standard against 8 above standard, hardly fair! You would have had to fill the tyres to 54psi to do it fairly! Road tyres are not really designed to work at 10 psi, or 54psi, so this is silly!

A more reasonable test would be wet road/roandabout type thing and runs with fronts set to extremes of 28psi min and 36psi max.

Alternatively, lets just go to MIRA and play with pressures there. Lets see if reducing the tyres contact really makes it grip better!

Moray