track day tyre pressure

[ralphb]

Can anyone advise what is the appropriate tyre pressure for a day at the track (Britdgestone 245/40/17s)?

[johneroberts]

6-8 psi less than normal is usually about right for a road tyre[img]images/graemlins/grin.gif[/img]
Cheers
jr

[Jani]

If we are talking about cold tyre pressure, I've found that outside front tends to "collapse", and wear it's shoulder and even side heavily, unless I have .1-.3 bar _more pressure than on the road.

So I tend to use 2.9 - 3.0 bar in all tyres (mine are 235/40-18). I'd suggest starting with 2.8-2.9, and lowering a bit if tyre does look OK after a few sessions.

[ralphb]

Given that 6-8 lbs psi is 0.4 bar, that means 2 responses ranging from 2.3 bar to 3 bar (based on recommended 2.7 bar). Now I know Mr JR is member number 3 [img]images/graemlins/bowdown.gif[/img], but I really wasn't expecting to be told to let some air OUT [img]images/graemlins/crazy.gif[/img]!! Anyone else want to offer an opinion. I reckon if I get 10 posts, I'll take the average [img]images/graemlins/grin.gif[/img]

[johneroberts]

ralphb,
im a track day whore and on my car, if running standard tyres i run at 38 cold, 3-5 laps i can guarantee that the pressure will rise 6-8 psi, if slicks used even more heat is produced so a greater increase in pressure.
But Jani has always been into tyres and stuff, but i would say thats fine in normal conditions, but a track now thats a different matter TRUST ME [img]images/graemlins/thumbs.gif[/img]
All the corolations are with a RS4 with various tyres and rims.
Cheers
jr

[Jani]

Hi Ralph & John,

I've done some 20 track events in the last 10 years with my ex S2 and RS2. Some have been with slicks, lately with road tyres. These are different worlds altogether.

With slicks I was adviced by race guys to start with 2.0 bar (29 psi) cold pressure, and lower if it would go over 2.5 bar. Slick is designed to heat and start to work, with road tyres it seems to be vice versa, overheat them and you lose all grip and get terrible wear.

Same pressure strategy does not seem to work with road tyre, at least in a front heavy estate / coupe like RS2 / S2 with McPherson struts.

The outside (usually left) front just does not cope with it's load. I get wear 2/3 or half the way to tyre's side (in a 40 section tyre very close to wheel!), and shoulder really wears badly. On top of this the tyre will overheat and start to come apart. And when tyre is on the side and not the tread, grip is not great either, so it is understeering badly.

Therefore I have had to raise pressure all around ( at rear too to keep handling balance). The 3 bar (43.5 psi) suggestion was my experience, things depend on the track and tyre too. If track has a little banked corners, it will help, and if tyre has stiff sidewall.

Maybe you should start with stock "hi load" pressure, and lower if possible. Just remember recommendations are always for cold pressure, and you will have higher pressure with heat.

I start to wonder if things might be a little different in S4tt/RS4, since these might keep front wheel camber better in corners, having multilink front struts?

[JJRS4]

I run either standard or 2 psi greater - COLD tyres. I would never let air out.

John, I know you do lots of days too, so I am interested in what you say. Are you not worried about tyre roll with pressures down?

[ralphb]

Whilst the pressure debate rages, I went to the yahoo rs2list site (what a nightmare to navigate [img]images/graemlins/frown.gif[/img]) But apart from that, I've become increasingly nervous about the 225/245 debate. Although Macca summarised it on this site and it seemed almost a debate for the purist, the actual debate between Jani and Pentalis about the safety (or lack of it) of non-dunlop 245's on 7" rims is alot more dramatic! [img]images/graemlins/shocked.gif[/img]

Am I really at risk with the Bridgestone 245s? Should I get a tow to the nearest tyre shop? [img]images/graemlins/tongue.gif[/img] Especially as I'm trackbound for the very first time... The only things about 'sidewalls' I was concerned about before reading this was not hitting one [img]images/graemlins/suicide.gif[/img], but now I'm totally confused... [img]images/graemlins/confused.gif[/img]

Also noted comments about the tramlining effect. I can certainly feel this. Is this my 245 tyres, or potential worn bushes, or both [img]images/graemlins/confused.gif[/img]

[Jani]

Hi,

you are right about yahoo web interface, a nightmare. Works OK with mail though.

The 245 issue on 7" rims has been discussed a lot, Pantelis has the worst experience definately. I'd say 225 is the safe and sensible choice, unless you find oem dunlop sp8000s. Some 245 tyres might work, some not.

As to tramlining, everything is relative, wide tyres always do that a bit, but excessive tramlining might mean toe out, caused by either worn bushes or wrong wheel alignment, or both.

Usually the worst place for wheel/tyre trouble etc is the open road, where you have oncoming traffic, lorries, people, family onboard etc. On track there is always at least a little runoff, you have a helmet etc, so I would not be _that worried. But in general this 245-7" issue needs solving, or at least one needs to be aware, and visually check from time to time.

[ralphb]

Jani

Thanks for the advice - it was indeed the bushes. Definately no more tramlining. I've just got the car back from a service and it wasn't even that expensive to fix.

Can't say the same for the replacement of the front brake pads, new electric water pump (leaking), minor crankshaft oil leak ('sweating' more than leaking) and sticky ignition (changed to avoid burning out the starter motor). GBP1000 later [img]images/graemlins/pftroest.gif[/img], but at least my new car is now certified good as new! [img]images/graemlins/grin.gif[/img]

[DavidT]

For trackdays I run standard pressures or higher, typically 38 front 36 rear on my S4. I have done the same with other cars for trackdays as well and never had any problems. They do go up significantly when hot (5-8psi) so you can only set them when cold.

The reason for this is to stop them rolling on the rims and to reduce wear on the outside tyre edge. It also protects the rims a little when going over kerbs or other things which lurk near - and not so near - the tarmac [img]images/graemlins/blush.gif[/img]

On the road higher pressures are an issue because they become bouncy and they tend to wear from the centre. Neither is a concern on the track with a smooth surface and where the vast majority of force/wear is exerted in the corners.

The other significant thing I have found is tread. The less tread the better with track use when the surface is dry. It is the heat build-up in the treads that reduces grip.

David