Tyre Pressures

[dejay]

I finally got round to getting the s1.5 back on the road for the summer, and I've just brought four new tyres, but i'm not sure what pressures I should be running with. I used to have the 205/60/15's which had 22psi front and 24psi rear, but I'm now running my s on 205/55/15's (cos' you can't seem to buy decent tyres in 60 profiles anymore!).
Does anybody have any ideas? Is there some formula to tyre pressures were you can work out what you should be running, or is it just down to experimenting?!

[GreenV8S]

quote:I finally got round to getting the s1.5 back on the road for the summer, and I've just brought four new tyres, but i'm not sure what pressures I should be running with. I used to have the 205/60/15's which had 22psi front and 24psi rear, but I'm now running my s on 205/55/15's (cos' you can't seem to buy decent tyres in 60 profiles anymore!).
Does anybody have any ideas? Is there some formula to tyre pressures were you can work out what you should be running, or is it just down to experimenting?!

I'm sure most of the track day regulars and race/sprinters will have their own ways of finding the 'best' pressure for the conditions, but from the sound of it you're more looking for normal road use.

Going from 60 profile down to 55 isn't a big change and I'd stick with the same pressures - 22/24 sounds about right to me.

I don't think there are any exact formulas for this sort of thing, it's mostly down to trial and error/experience as you say - but there are some common guidelines which will be applicable to most TVRs.

If you have the same tyres sizes front and rear, then you probably want to run the rear a couple of PSI harder than the front to improve the high speed stability. If you're running a wider tyre on the back, this is less necessary and you might drop the rear pressure, maybe even running the same pressure all round. But never run the rear softer than the front.

Apart from making sure the left and right pressures are exactly equal, and the rear is a little bit harder than the front, the actual pressure isn't all that critical. Changing the pressure does affect the amount of grip slightly and effect the car's handling slightly, but the effect varies depending what type of tyres you have, what condition they're in, how your suspension is set up, what the road conditions are, how you're driving, etc. There's no one 'optimum' answer even for the same car and tyres. I've run the same tyres from 20 psi up to 30 psi, and although I could feel the difference in handling, the car was still perfectly driveable and I had to look at the lap times to see the difference in grip.

Hope this helps,
Peter Humphries (and a green V8S)

[dejay]

Thanks Peter, I'll take your advice and see how they go with the standard pressures and I'll keep an eye on what the tyre wear is like.