Tyre pressures

[stephen low]

Remember reading a thread on pressures but can't seem to find it again and am keen to have some nominal settings for the car for this weekend's track fun.

Running 15" 245s front and 295's rear.

What pressures do you folk set?

And can I assume these are measured as cold temp pressures?

Cheers

Steve

[Wazza]

I'd suggest 40psi...( Hot)
That should be close.
Cheers,
Warren

[dallas_]

Interesting.
I've found 24 -26 psi hot works best for my car. That's a much larger range than I would have expected.

[Donunder]

Originally Posted by dallas_

Interesting.
I've found 24 -26 psi hot works best for my car. That's a much larger range than I would have expected.

I think the conversation here is about track pressures for road tyres.
26 psi is fine for road work, but all sorts of drama would ensue if you took to a race circuit with only 26 on board.

[dallas_]

Interesting. Those are the pressures I run on the track. I use a tire pyrometer to measure tread temperatures on the outside, center and inside after hot laps. If the pressures are over that range, the center temps read highest indicating the tires are over inflated.

Not saying this is right for any other car, just saying what works for my car.

[boxhead]

A huge variation regarding the tyre size and construction.
Steel belted radials are better with higher pressure.
Canvas billboards are better at the lower pressure.

[dallas_]

Maybe you guys down under just have higher quality air.

[stephen low]

Thanks guys for the commentary and hey Dallas

You're right we are full of it down under......air that is - lol

Anyway did a check and the car post alignment had seen the tyres set essentially at 33 all round cold.

I start with that and see what transpires at is driving ok on the road at this.

But I think the loose nut behind the wheel is more likely going to need tightening first anyway to get any substantially performance going.

My goals are to try and not hit ANYTHING!!! and perhaps a sub-two minute lap to start with simple goals for a first start.

Am out to have some fun but given my history there is quite some trepidation with speed and large concrete barriers to stay clear of.

Wife has already said she'll cut off some low hanging fruit if I do indeed dent the car.

So if it can buff out I'll be safe - ha.

See all those coming early tomorrow morning.

Steve

[albanycobra]

i just did a street circuit round the house's meet in my GT40, so racing on the road...best of both worlds with 15inch Avons ,started with tyres at 28psi .This was still to high, going to drop down to 25psi next event.

[SPF1061]

Originally Posted by Wazza

I'd suggest 40psi...( Hot)
That should be close.
Cheers,
Warren

Wow. 40 seems way high for light cars. I think experimenting with between 25-30 cold should net a pressure that feels good and handles well.

[Bernica]

40 lbs is way too high IMHO.
23-28, maybe 30 max depending on your conditions. It's a very light car and rule of thumb as I recall, rule of thumb is 1psi for every 100lbs of weight.

[Wazza]

The instructors at Queensland Raceway do a big "safety talk" for anyone running street tyres on the race track.
Inflate the tyres to approx 40lbs. Hot....in the case of. Car sliding sideways,it will stop the tyre from rolling off the rim,wheel digging in to the track,and possible roll over.
But it's up to you....
I'm not the one driving the car,and I can see what they're getting at,but I also feel,you'd lose some grip without the tyre flexing a bit more.
Too many experts around to get the right answer I suppose.
Cheers,
Warren

[dallas_]

Warren,
I feel like this is the kind of thread that can help people gain useful information. Hopefully it will do that.

There are too many variables to answer "what should my tire pressure be?" When I was trying to figure it out for my car I got a lot of conflicting information and opinions. There are so many different car and tire combinations that the range of answers wasn't really useful. As others have pointed out, our cars are light and that is an important factor.

Here is one of the articles I came across that I found helpful: TurnFast! Race Driving Techniques for Heel Toe Downshift, Driving Line, Cornering, Braking, and More • Tire Pressure 1

That was the article that prompted me to purchase a tire pyrometer. Knowing the temperatures seems to be the most accurate way to get the pressures correct. And getting tire pressure correct is important on the track so hopefully more people with knowledge will weigh in here.

John

[96Cob]

My personal rule is... street tyres on the highway... measure pressures cold....after an hour or two on the highway they have raised 1-2 pound. More than 2 pound they need more pressure.. ie, they are getting too hot. At the race track tyres will work harder so start 5 pounds lower cold. Street tyres only. Please note... my name does not start Guru Shwami... lol

[scottj]

Originally Posted by SPF1061

Wow. 40 seems way high for light cars. I think experimenting with between 25-30 cold should net a pressure that feels good and handles well.

Originally Posted by Bernica

40 lbs is way too high IMHO.
23-28, maybe 30 max depending on your conditions. It's a very light car and rule of thumb as I recall, rule of thumb is 1psi for every 100lbs of weight.

I have a performance driving book by Bondurant that was written during the period when he used Superformance Cobras. He stated in the book that he ran 40 psi in street tires on those cars for the track or any aggressive driving. It stabilized the sidewalls. Now, I'm no expert, but Bondurant on the other hand...

[stephen low]

Guys thanks for all the input. Do understand the variables issue but just initially needed some guidance. Ended up playing a bit.

Started with the tyres as set by the wheel alignment mob as 33 cold about 37 hot. Lots of tyre talking in the corners but reasonably behaved. Dropped to 30 and then 28 hot over successive sessions and believe this helped get a bit better turn in bite. Times improved each session so I think I was heading in the right direction.

Had a fun day too without any significant issues mechanical or otherwise and spun twice so I was pushing myself.

Cheers

[fastd]

i think it also depends on the tire brand and side wall flex. the avons sidewalls are very stiff. i recall that the guys from ERA told me to reduce psi in avons when tracking so that the tire would "roll over" (I actually don't know what that means but he said it)

[Treeve]

The tyre manufacturer should be able to give you good advice if they're an R-spec tyre. If not, then look for an R-spec!

[DaleG]

24 PSI all around, cold.

http://www.ffcars.com/forums/17-fact...-pressure.html