I've come to grips with different anti-roll bar settings and how they affect handling (stiffer rear bar promotes oversteer, vice versa etc...) but I'm not exactly sure about how tyre pressures affect handling. I think that the following is correct: Lets assume we have a tyre with a flat contact patch at 30psi, if we increase the pressure to 35 psi we will have changed the patch to a U shape with the centre of the tyre having the most contact with the road and the sidewalls having less contact with the road. Conversely, if we reduce the pressure to 25 psi we will have changed the patch to an upside down U shape, with the middle of the tyre having less contact with the road, and the sidewalls having the most contact. What I'm not sure about is how each pressure (25/35 psi) will affect the handling and wear rate of the tyre. If any of you have experimented with different pressures at trackdays then i'd appreciate your input on what settings will make what differences to the above example. Thanks!
dont think that is quite correct, i'd say in additon to that i think what happens is that the sidewalls flex more and cause some odd handling due to the movement
Different pressures result in different temps too, and not always consistently across the width of the tyre. Temps will also vary depending on driving style, just go play and see.
Yeh the lower pressures make the tyre sidewalls give more (collapse), the ide with running low tyres on track is that after a couple of laps they have heated up more giving higher pressure. Some people set the pressures hot, let the tyres cool down an note the cold readings, depending what track you`re on these will differ. Have a play, but personally I don`t like sub 25 cold pressures, quite scarey!
Recently there was a double fatal RTA locally - after investigations they found that the cause of the accident was over-inflated tyres......
so its an idea to set your tyre pressures lower than optimum on a track as the tyres will heat up causing greater pressure, which could then be the optimum pressure. So is there any advantage of overinflating tyres? Is the ideal pressure where the contact patch is perfectly flat under normal road conditions (minimal heat getting into tyres)???
Higher pressure gives less rolling resistance. I tried 42-44 PSI all round once and it sharpened up the handling but broke your back (on the road).
so - does higher pressures necessarily give better handling (if the tyres arent going to heat up that much) or are you better off sticking to recommended pressures for road use? Still not sure whether higher/lower pressures will improve grip at the same tempreature???
As Keith says, we play about with pressures at the track days, it doesn't cost anything and it's easily reversible Clockwise track, the NSF tyre will get the most loading, so will increase pressure as it heats up. Some say pump the tyres up 5psi over road settings for the track I tried this and found about 3/4 way through the session the car would be sliding all over the place, also seen the NSF tyre go up to 40+ psi at Bruntingthorpe So, I let mine down to 23-25psi cold and they never get above 30psi and grip stays consistent through the 20 min session. Seems to work for me ok, but when cold the tyre feels as though it could pull off the rim the first time you go down Craners at Donington I'd say stick to standard pressure on the road ( I use 2.1 bar (30ish) all round) One tip that I learnt from Ian Carvell, in the wet on track reduce rear tyre pressures by 5 psi, keeps the back end more stable. Edited by: G_V_K
It's all about striking the right balance, and since handling is so subjective then you're best off trying it out yourself. Change it, if you like it and are confident with the car like that then great, if not change it again. What feels 'nice' though might not be the fastest.
I read a bit about Veloqux (sp?). They normally prepare cars for race series but they've now got a track day side of the business where you basically get one of their engineers to garage and prep your motor and tune your motor/give advice at your track day. They send their track day drivers out for a couple of orientaton laps, pull them in check the pressures and temps across, make adjustment, send out for another couple then back in again. I can't remember the exact process but I suppose you can't turn your nose up at advice like that.
That's not the whole story, you need to think about how the weight of the car distorts the tyre along the wheel, as well as across it. If you increase the pressure, then the wheel tries to stay more circular, and the contact patch gets much smaller front to back, as well as going slightly domed. So you get a much much smaller contact patch. This will reduce the rolling resistance (less hysteresis loss in the rubber), make the ride firmer and drastically reduce the grip. When I lived in Canada, you could reduce your tyre pressure to 10psi if you needed extra grip in the snow. It made the contact patch much bigger, and hence gave you more traction in the snow. Simon.
Aye. Its so that you can adjust the contact patch size and as such the grip at front compared to back. The benefits of high tyre pressure is that the tyres are more predictable and the tyre has less tendancy to roll over onto the sidewall during cornering and slightly improved transient responses (ie more direct steering through left - right - left corners). The benefits of lower pressures are that you get more grip and a smoother ride. If you are on the track you can measure your tyre pressures and temperatures with a tyre pyrometer and this can be used to determine what part of the tyres are getting hot (inside, outside) and then either adjust your camber or adjust your tyre pressures to produce an eve temp across the face of the tyre. Tyre and camber stuff
Remember; weight distribution, spring & roll bar settings will effect the pressures you want to run in your tyres & vice versa. Inflating & deflating a tyre (by even a small amount) can move enough weight around to have a (small) effect. I didn't think the amount that shifted was notable untill I played about on the scales one day! Edited by: Pike
I suppose on track you can try all sorts of pressures, if you loose the car you`ll just hit grass normally. You need to be more conservative on the road as it`s not just grass you`ll be hitting!
01582 471471........Yokohama Motorsport Speak to them.......extremely friendly and good advice For my Mk1 they advised starting off with the standard COLD SET pressures.After the first track session immediately check the (hot) pressures and note the pressure rise to see how much the tyre is `working`. With a standard road tyre as long as you`re increasing by up to 4# then that`s OK - leave alone on the front. Motorsport tyres will increase to a higher degree. Recommendation was to leave the fronts well alone (24# COLD) but gradually increase the rears as the day goes on and see how things feel. I let the tyres cool down to COLD SETTING then increased from there each time. Ended up with 40# COLD SET which gave excellent handling. Edited by: jamesa
