stv951

Hello,

will be taking part on a Porsche trackday tomorrow and monday, and have still not decided on what tyre pressures I should use.
Here are the specs

Toyo R888 (R compound) on 17 Cup wheels with stock sizes (225, 255)

2 deg front and rear camber
Almost 0 toe all around
3 deg caster

Stock M030 Koni suspension lowered height
968 M030 anti sway bars

I believe that the factory 36 fr, 44 re tyre pressures for 16" wheels is very high.

Any ideas and suggestions ?

DanR

i presume you are running in greece in about 70 degrees ambient. WHen it is similar in the US I run toyo ra1s and start at first session 30 all round. Normally find that I am up around 38 at the end of a 20 minute session. Not run 888's yet

Spidey944

38-40ish is what u want in most instances.

951_RS

Don't want to make other people sound like they dunno what they're talking about, but you probably shouldn't just go off someone else's pressure recommendations. Too many variables from weight of your car, suspension set up, weight distribution, humidity, temperature, everything factors into it.

So the only way to tell what tire pressure you need to run, is by using white shoe polish. Crazy, huh?

Start by putting the tire pressure at about the maximum manufacturer recommended pressure maybe a little less if you don't feel comfortable with it. Then draw a line with the white shoe polish onto the tire starting from a little above the tread down the tire past the tread a little bit.


After a few runs when the tires are heated up you check the shoe polish.
If the line of shoe polish still runs up past your tire tread then you need to lower the pressure.


If the shoe polish is worn off down past the end of your tread (onto the sidewall) then you need to add pressure.


This lets you know what each individual wheel is doing and how far onto the sidewall your tire is rolling onto
Here is what you want to see when your tire pressure is right.

DanR

I hear what you say about many variables but using shoe polish as stated above does not give the full picture. It may indicate amount of tire roll but it certainly does not give pressure or heat measurement. If you REALLY want to do it correctly use a pressure gauge and a pyrometer. Check the tire pressures and also the tire heat with the pyrometer across the width of the tire. You can then ensure the tire is operating at correct pressures and temps.

951_RS

Yeah I kinda forgot to include the pyrometer part to insure heat is distributed evenly and that they're up to operating temps, but I thought it was a given to use a tire pressure meter

333pg333

I find that R888s work best at about 32-35 hot. After that they get too hard and feel like they're definitely loosing grip. Anyway, build up to speed and play around a little. The other thing to think of is that if you lower them too much make sure you have access to a compressor otherwise your stuffed for the day. If the day/track temp is moderately hot, I would go out with 28-30psi in them and come in after a few laps to check your pressure and temp if you have pyro.

Ski

+1 on the pyrometer and do it just off the pit entrance, have a friend there to take the measurements.

TonyG

I run NT01's.

I run 38psi cold, which warm up to around 42-43 psi hot.

This, combined with the correct camber (approx 2.75 degrees) , gives very even tire temps across the tread width.


TonyG

DanR

Tony, out of interest what is the ambient temp when you are running? 4 degrees swing cool to hot seems quite low on your NT01 vs what I see on my RA1's

LUCKY DAVE

In addition to R6's, I sometimes run 888's, 275/40/17's on 9" rims all around with 725/864 pound springs on JIC Cross coilovers. After much fiddling, 3.7 degrees front, 2.7 degrees rear, straight toe rear and 2mm toe out front has turned out to be right for my car. It's darty, but the grip is wonderful.
I shoot for 38~39 psi hot when on 888's. This pressure seems to give the most grip, but sudden(ish) release. They're a lot more predictable at 34~35 hot, (crawly feeling) but there is considerably less grip. Any more than 40 psi hot and grip dissappears.

333pg333

That's some hefty springrates you got there LuckyDave. Is your car a daily driver?

LUCKY DAVE

No. It's a dedicated track car with a license plate. In other words...."street (il)legal"
-the pic in my avater is an old one-