Newman Boy

I went to driving school last month at Putnam Park. Recommendations from the forum for tire pressures seem to be 26 psi cold. I was not too enthralled with how the Great White Shark held in the corners. Then I did a strange thing. I check the owners manual. 36 psi cold was recommended.

Friday, I went to a driving school at Mid Ohio. Track was wet in the morning with light rain so first three sessions were primarily follow the leader. 90 minutes of track being closed. However, I did get three sessions with the track dry. The difference in how the beast stuck was remarkable. Therefore, I recommend 36 psi cold as does the owners manual.

I will give you a write up later. Suffice it to say, I had an instructor that was phenomenal. He raved about the beast. In every corner he kept saying "it will hold, it will hold." And it did. He could not believe the brakes or the acceleration. When we got to a corner he would say "attack.!".

That was great fun.

Jim

TennisFreak

I don't agree with this at all.
As the tires warm the pressure will go up and you will be letting air out.

Starting at 36 would put you into the 40s in no time.

Waaaaaay to much pressure for the track.

eboggs_jkvl

Yup, 36 cold will bring out the blisters on the center tread of your tires.



Elmer

hisvett

Working temps for the track; mid 30's. Once you get into the 40's, traction starts gong away along with overheating the tires.....not to mention throwing a code.

Sneakytoot

I just got back from Ron Fellows / Spring Mountain and they run there tires 26 psi cold and after a warm up lap they are the proper pressure for racing..........

four0nefive

Why would you want tire pressure in the mid 30's when the tires will heat up and increase in PSI????? The more tire pressure, the less grip, that's why it makes sense to start at 26 because they would most likely expand to 30-32 psi or even more in one session.

Len44

Interesting discussion. Anyone care to address the role of tire flex and the role it plays in increasing tire temps? If a tire starts out cold at 26 degrees, will it's temp rise the same amount as a tire that starts our cold at, say, 29 degrees? Why or why not? Show your work.

Also, the placard in the door jamb specifies tire inflation at 30 degrees (for every day / normal driving). Is this what most folks here recommend for daily (non-track) use?

Thanks!

jcp911s

This depends entirely on how you drive, the construction of the tire, track temps, weight of the car, etc, etc.... it's a black art, and everybody has their own preferences.

A novice who is driving 7/10th at a DE will not put as much heat in the tires as a racer driving 10/10ths... "cold" pressures don't mean anything... its the "hot" pressure that matters.

Typically, I run a full session in the morning, and then immediately bleed the tires down to target operating pressure in the hot pits... as the day goes on and heat builds in the track, you should continue to adjust hot pressure after each session.

Plus, tire construction matters a lot... street tires typically have more tread material, and heavier construction. Compared with racing tires, they tend to heat up more slowly, but also cool down more slowly, so when driven hard, heat keeps building and building, and they overheat.

For a baseline, I'd keep the hot pressure for the tire below 40PSI, and then go from there.

Newman Boy

See 10-57 of owner's manual. I was wrong. Should have been 38. I was not driving at a sustained 100 mph. Maybe 125 on back straight and 99-101 on front straight. My driving is certainly not I would probably do at Ron Fellows as I suspect the instructors know exactly what their cars are capable of and will push students closer and closer to that limit.

With my CTS V coupe it was 37psi.

Thanks for the input. I am still dazed and confused.

fdxpilot

The section of the manual you seem to be referring to is page 10-57 , which concerns high speed highway driving, like in Germany or the Middle East. For these situations, GM says start at 38 psi. However, you are at the track, and page 9-6 specifically addresses track tire pressure, saying to set cold pressure at 26 psi.

jcp911s

It isn't straight-line speed that builds heat, it is cornering force. As lateral G-Force builds up, it creates friction... and friction = heat. Street tires have tread that flexes, creating more heat. The tire carcass stores that heat... the more material in the tread, and the carcass, the more heat it stores.

Heat+Air=Air Pressure.

Manufacture's recommendations are written by lawyers protecting Mega-corporations from being sued... (the owners manual is the last place to look for track information.)

My recommendation is simple... keep a good pressure gauge in your glovebox. Do a session, pull in after a hot lap, immediately check your pressures, and "bleed" them down until the hot pressure is under 40PSI, and then do the same after every session.

meyerweb

Page 9-6 of the 2015 owners manual (Track Events and Competitive Driving):

Not sure where the OP saw 36 psi for the track.

JCP has it right, though. For track use, check pressure and tire temperature hot.

Jay_Davis

The track preparation guide also says 26 psi.

I've been setting them to 28 cold. From highway driving, by the time I get to the track they are at about 30. After a couple of laps they are at 33 and don't seem to ever get above 36. So far that's been working fine.

owc6

I can see where the confusion may arise. From the '14 OM p. 10-52:

"Tires require inflation pressure adjustment when driving the vehicle at speeds of 282 km/h (175 mph) or higher, 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. See the example following. Return the tires to the recommended cold tire inflation pressure when high-speed driving has ended. See Vehicle Load Limits on page 9-13."

On the 2015 OM, it's p. 10-57.

MrGTC

This thread will confuse a lot of people and misinform even more. OP, do you think you can at least change your title and add a "?"? I had to click on this thread and read through everyone's comments just to find out that what I had in mind (26psi cold on track) is still correct.

Newman Boy

I stand corrected. I admit I was wrong. I have cut my Brezhnev -type eyebrow in two and cut the left side off.

I always tell my daughters when they asked me about their cars to read the manual. I should have read the entire manual. Nothing like eating crow but they do not follow this forum so I should be okay.

I apologize for my part in causing all this confusion.

Thanks for your response.

Jim

FKING1

Have been Autocrossing & one Track Day at 38.
No issues & the Z51 handles great.

Steve Garrett

Updated thread's title.

MrGTC