M3 CS-Track Day Tyre Pressures...?

[RatBoy M3CS]

Hi Guys..

Im looking for some info on track day tyre pressures to take a bit of the trial end error out of my next track day...

I ended up with hot pressures of 44rear/40front on the last meet which gave me a reasonable balance on the car, but i'm looking to dial out some of the turn in understeer i'm getting, i chalked the side walls and dropped the pressures until i ended up with a contact patch that was almost at the edge of the tread blocks, on PS2's..

Anyone got some more info from experience..? ambient was Zero C on the last event.

Secondly: How much negative camber can i get out of the stock OEM front turret top blocks..? i'm on stock -1 degree front settings at present with -1.5 rear.

[taffyracer]

chalking the side walls is a good idea, i found about 40 on PS2 was about right, any less and the sidewalls flexed too much, road tyres need more pressure, so many people go the other way and cock it up

[m12_nathan]

I found that about 32 hot was good for me, any more and the temp gun showed only the middle of the tyre was being used and there was bugger all grip.

[taffyracer]

i tried 32 ages ago and the sidewalls were completely shagged, couldn't even read the michelin text, that's how far they rolled, would strongly suggest not going that low

[m12_nathan]

Agreed that the sidewalls were shagged but any higher and grip was compromised as only the centre of the tyre is used. Tyres are consumable so I chose grip over tyre life

[taffyracer]

yeah but if the sidewalls were shagged then the tyre is rolling too much, 32 is the max you'd expect a slick to run at when hot and the sidewalls on those are way stiffer to cope

[m12_nathan]

But any higher and the grip falls away massively and the temp gun shows the tyre is over inflated. I guess what it really shows is road tyres are crap on track.

[RatBoy M3CS]

Thanks for your input here guys... i will try a few pounds lower next time round, until i have max tread block on the tarmac, but i cant see it being any lower than 38-39 hot... as suggested the tyre wall flex will be too much for my liking for a crisp turn in...

But a lot of it is trial and error i guess... 32psi must feel 'orrible for steering response surely..?
I found that at 40psi hot, the front edges were getting too hot and the rubber was more like chewing gum which you could pull off with your fingers...

I'm looking into a set of track rims now and it looks like 18" are the ones to go for as Dunlop do a good range of boots for them in that diameter.. who makes 19" slicks and are they stupidly expensive..?

[m12_nathan]

for me that is easily offset by not understeering off the circuit due to over inflated fronts Guess it is a personal thing. Get a tyre temp gun and you can see what your tyres are doing, over inflated, under inflated, too much camber, not enough camber, really useful.

[RLK500]

The problem with using road tyres on track is the compromise. You inflate higher to prevent the tyre being forced off the rim and to create some stability, which then reduce the grip levels. I found this when racing and having to use a road tyre as it was the control tyre for the series. Ultimately we would have the tyres buffed down to a tread depth of about 2mm. This reduced the drop in grip issues as the tyres no longer overheated due to the tread flexing, while still being able to run relatively high pressures. However, in the wet you would be off the road in a flash. So either find a set of relatively shagged road tyres and pop them on spare rims, or run R compounds (Yoko A032/048, Toyo's, Dunlop's etc). Long term you will probably find it cheaper to run R compounds as they last a lot longer than road tyres on track.