I'm having some fun at the weekend and wondered what the best pressures might be for an MY03 WRX on track. IIRC it's best to up them, but by how much?

Cheers.

I'd be wary of over inflating tyres as they do heat up and cause the air inside to expand, so be careful.
Likewise unless you know what temperatures you are going to come across "on the day", it is very hard to predict as to what pressures you should be running. I would strongly suggest asking someone else "on the day" who is actually there and has run this circuit before, so has some previous knowledge as to what works and what does not.
You cannot simply adjust tyre pressures to a given pressure and then "expect" them to perform. try asking someone on the day and get much better information.

Have a look in the driving dynamics forum. There is a good piece written by John Felstead in setting up tyre pressures.

From memory between 35 and 38psi seems to ring a bell. But as they warm up you will need to release air.

ps. See you at the Brickworks. ;)

Damian.

I was thinking of dropping my pressure by a couple of psi for Saturday, I was also thinking, that the hotter the tyre gets the more the air expands. Not that i'm planning on driving out of my capabilities or wasting my tyres

BTTT for some more ideas

Phil

Advice Robbie Head was giving out at a dealer's trackday a couple of years ago was to run 50psi all round

If it is dry start by adding 6psito your normal pressure. Add pressure to the end that breaks away. You will soon find when you are over inflated. You may also be surprised that front pressure can exceed 40psi.

That sounds more sensible Harvey, cheers.

GM, tried that on the advice of a certain 'figurehead' from prodrive. Killed a set of tyres in 6 laps, although it was a hot day.

Run +6 as harvey recommends. Get half a dozen laps under your belt then check pressures (stop first;)).

Back pressure off so that you're back where you started, ie +6ish above wht you would use on road.

I like to run the fronts harder than the rears, but it all depends on your driving style.

simon;)

ps. if its wet ignore everything above.

I was told yesterday that +4 or +5 is a good starting point. Will bring along the trusty halfrauds digital tyre inflator thingy.

I've got one of those thingy's too ;)

I've got one of those thingy's too ;)

So do I, the pressure gauge on it is not too good, you need to set it to aim over by about 4 psi. Check you pressures with a good gauge as well.

Get half a dozen laps under your belt then check pressures (stop first;)).


Surely you'd get a more accurate reading by not stopping first?

i normally put about 36psi in when cold, go out for a few laps and check them again when up to temperature, if they are around 42psi your're in business ;)

i normally put about 36psi in when cold, go out for a few laps and check them again when up to temperature, if they are around 42psi your're in business ;)

EXACTLY ! By starting with lower pressure , the tyres even tend to heat up quicker , and during trackdays...time is money :)

I found with my classic on 16" wheels, road pressure 34F 32R I tracked them at 42F 40R and the edges didn't melt TOO much

Mind you I've never tracked with tread over 4mm

Faire D'Income,
how do you check them without stopping?

simon;)

Faire D'Income,
how do you check them without stopping?

simon;)

It be a gag Simon. I was going to theorise on pressure differential correlations with a drop in tyre temperature as a result of stopping and other stuff I know nothing about.

:)

that'll be two of us then...;)

Hi

I am just wondering what you are going to achive by increasing the pressures?

reduced wear to the shoulders of the tyres, plus it stops them rolling off the rims at speed if the pressure is too low.

I see what you are getting at, suppose it depends what you want to achieve, but if you increase the pressure so the tyre is rock solid then the only thing that is going to move around is the tread block.

I don't think this is a good thing (depends how deep the tread is). Sure a few psi increase is ok but I don’t think >40psi is going to be helpful, after 20 mins on track you are going to be looking at 50psi...

I have not got too much experience of this sort of pressure as I am used to setting up from 14psi to about 20psi (much lighter car) but I know the 6psi makes a very big difference to the handling. Suppose its down to everyone’s own taste.

Suppose if you want grip you need to look towards ACB10 or AO32R - is the oil system in the scoob capable of taking high G?

40 psi ludicrously high. Whatever you start with pit after 5 laps or so in the dry, check and reduce. 20 minutes far too long- tyres can overheat and de-laminate very easily depending on track temp, abrasiveness of surface etc etc.

Never had any oil issues although theoretically they could prove a problem.

Running slicks. Rarely run road tyres as far too expensive to destroy.

Most track days are sessioned down into 20min sessions though...

It is really interesting the tyre pressure issue. I am using BF goodrich, 16" 40 series, and i cant stop the sidewalss from tucking in. I am up to 34 psi cold on the fronts and really dont want to go higher than that as it simply is not right. With the pressures mentioned below you are definately reducing maximum potential grip.

So the answer must be in the geometry of the car etc, maybe adding a bit of camber..so does any one know of any good places to take the car too to get it set up for handling?

The ideal geometry settings for the impreza are quite well documented, although there are obviously a lot of differing opinions and no definitive answer as to what is 'best'.

Talking from a trackday perspective, you want a healthy dose of negative camber all round. You will usually be able to get more on the front than the rear- my clio racer has so much neg camber that it looks like the wheels are going to cave in!

Caster is the adjustment that will have the most pronounced effect on your handling, as it will determine the amount of natural understeer / oversteer.

I think I read a really good explanation of camber and caster on here somewhere- i won't attempt to get any more complicated as I'll only confuse myself;)

Most good tuners can recommend and set your geometry and believe me it will make a massive difference if you haven't had it set before. It can, however, adversely affect tyre wear and can also affect wear on other components- for instance we change the wheel bearings on the clio every 12-18 hours of running as they're prone to failure due to the combination of massive stress of massive negative camber and warm slicks- although it would never be this extreme on a road car.

hope this helps,
simon:D