boofus1

The standard recommended cold air pressure is 30psi. However the manual says for high speed driving (100mph+) to do cold pressure inflation to either 38psi or the recc'd max psi stated on the sidewall whichever is less. For my sidewalls that is 51psi.

So is it advisable to put the cold pressure psi up to 38psi for an HPDE?

Greg00Coupe

Maybe go over to the autocross/track section of the forum.

PeteC7

I'm doing my first HPDE next month and I specifically remember 26 psi being the recommendation from both the manual and the Ron Fellows mechanics. You definitely want to run lower pressure than the street since you will be putting more heat into the tires.

boofus1

Thanks. That makes sense. What puzzles me is that on page 272 of my owners manual it says this:

The tires require inflation pressure adjustment when drivingthe vehicle at speeds of 160 km/h (100 mph) orhigher, where it is legal. Set the cold inflation pressure to the maximum
inflation pressure shown on the tire sidewall, or 265 kPa (38 psi), whichever is lower.

PeteC7

Page 165 lists the 26 psi that I referenced. For HPDE events you will only be operating above 100 mph for a couple seconds so I don't think your reference applies however I can see how it can be confusing. There is a big difference between a short burst of speed and sustained cruising at 150. If I was doing sustained top speed runs on an air trip I would raise the tire pressures substantially like they recommend.

Indy-hp

The question was asked in my Spring Mountain class. They check pressures and temps after each session and aim for 34-38 warm. The owners manual recommendation for 38 cold is for sustained driving above 100.

boofus1

Pete, THANK YOU! Agree I certainly won't be doing over 100mph for more than a few seconds at a time. 26psi sounds a lot better. Really appreciate the insight/quick response.

rb185afm

I started at 30 cold and ended up at 37 hot. I had to drop to 27 to 28 cold to attain 35 hot. This was at Buttonwillow Raceway with 65 to 70 degree temps.

christopher walton

I am running nitrogen in my tires. So should i run at the upper limit since there won't be any heat or cold pressure fluxuations??

PeteC7

Air is mostly nitrogen (~78%) so not going to be a massive difference. Since it's easier to remove air than add, I'd start higher and bleed down from there. On your cool down lap flip over to the tire pressure display and if they are over 35 hot then just bleed out a couple extra psi.

JMII

This is what I tend to do. 26 PSI is the recommending starting point cold. As mentioned the tires will heat up and the pressure will increase.

VENOM ACR

I run them around 26/27 psi cold. After the track day though, I will bump them up to about 39 or 40 to try and even out the wear. Lower pressure causes the outer part of the tire to "roll over" so by bumping up the air after track days, it relieves the stress on the outer edges and allows the rest of the tire to wear.

That coming from an employee/friend who works at Michellin and tracks his C6.

jimmbbo

OP - I have found that 26-27 PSI runs the tires up to 36-38 after a run on the track, depending on air/track temperature and how aggressively I drive.

As a gas, nitrogen obeys the ideal gas law, which means it expands and contracts with heat according to the law, providing no realistic expansion difference between it and air, since air is 78% N2, 17% O2 and the rest water vapor and trace gasses. Nitrogen's main benefit is to reduce moisture and tire degradation from oxidation. For performance cars that replace tires relatively frequently, the additional cost and hassles of using N2 seem to offer little real world benefit. Just sayin'.