Tyre pressures

[CycleSi]

Just a quick one.....

To reduce understeer, should I increase or decrease my front tyre pressures.

Last time I played with front pressures I could have sworn it increased the understeer but have just read some old posts on the site and one of them said understeer will be reduced if you decrease front tyre pressure?

Now I'm confused !

I have an AK with a 400ci SBC weighing 1180kg, 47% front & 53% rear weight distribution and currently running 25psi front and 20 psi rear.

Thanks...

[Purple AK]

I'm running 20psi front and 18 rear. I'm sure 25 is way too high What Wheel/Tyre size are you running?

[CycleSi]

16" rims.
215/55 x 16 and 245/55 x16 Toyo Proxes T1-S.

As I say, when I dropped the front tyre pressure before it seemed to increase understeer?

[Purple AK]

Erm Same size here. Is your tracking Ok?

[CycleSi]

I think so.

It has been corner weighted, aligned, tracked and checked by Northampton Motorsport so it should be fine. It handles well enough, it's just that when I "push" it the front tyres squeal a bit and the front end goes "light".

[wilf]

BEB - I am not sure that a change of tyre pressure will make a huge difference to the understeer characteristics of your car. It is a finesse thing really, and if you want to radically change the cornering behaviour, then I guess you should be looking at spring rates or, more likely, fitting an anti-roll bar at the rear.

Someone correct me here if I have gotten it backwards, but I think that fitting an anti roll bar on the rear makes a car oversteer more (or understeer less) - is that right? I put my hand up right now and admit to not being a suspension specialist!

I suspect that the natural tendancy of these cars would be toward understeer, power oversteer being available at the flick of a foot!

[CycleSi]

Wilf,

You might well be correct about the tyre pressures.

I did get AK to fit their newly developed front anti roll bar last June which seemed to help

I started the post simply because most fellow Cobra owners seem to run lower tyre pressures than me and it got me thinking about mine. If lowering them won't make much of a difference then I might as well try it as if nothing else it might help reduce the tendency of the front brakes to lock - more grip, etc.

Bu then again, that's a new subject of debate altogether

[427scr]

A simple solution to understeer...

When the front feels light, just stick your right foot in.

Assuming you have a real engine, all the understeer suddenly changes to oversteer, bang on some oppostite lock and bobs your uncle.

Failing that, I run 19psi all round and I don't have an understeer problem at normal road speeds. I have noticed at very low speeds (car parks etc) that the car dosn't want to go round corners and the front wheels skip sideways. However, my old Astra Sport used to do that and I now have an Alfa GT that does the same thing. My theory is that if the production boys have a similar problem, why worry too much.

[nbracken]

Beb, I have similar tyre/wheel set up to you and your fronts look higher than most by some margin and the rears soft.

There are plenty of posts on teh site and you'll see that most people run in the range of 19-22 psi with 1 or two difference between back and front.

I run with 21 front and 22 rear

As Wilf says it is a trial and error thing really so get out there and experiment. But there are also other influences such as anti roll bars, camber and spring rates.