Never taken something this heavy on track. Any insight into tire pressure appreciated.

I plan to aim for 35 psi hot???

 

The general aiming point is 32-24 sitting in the pits, and 40 coming in of a lapping session.
If the tire feels greasy its too hot and likely too much pressure
If the tire feels like an eraser scrubbing across the road, it is not hot enough and too little pressure

But a probe tipped tire pyrometer is what you use to find out the correct pressures for your driving style.

 

Gm said 23 front and 24 rear psi cold

 

Every situation is different, and even for a given car/driver/track/day combo, the pressures producing the best performance may not be the same as those which produce the best wear/longevity. Only way to know what's best for you is practice and experimentation.

For a modern radial tire on a car with good camber, 35 hot should be in the ballpark.

 

A lot of people check and adjust pressure throughout the day. Start around 30 - 32 cold and check and adjust downward as the pressure increases. If you ever autocross, you'll see most people checking the pressure after almost every run. As other's said, around 35-37 hot tends to be where you want to end up for most track tires.

 

Start with the GM cold recommended pressure then run the first session and see what your tire pressures are after coming off track. Don't adjust right away. If you are like me the first session of the day is my warm up session and I don't usually push the car as hard as I do in later sessions. Wait until after you finish the second hot session and see what pressures you have then and if you think you need to adjust them to make the car feel better to you.

My C7 Z06/Z07 which weighs 3560 lbs with not a quite full gas tank and I have found my best hot pressures are 32/33 psi at all tires. Not sure what the weight of a C8 is but I suspect it is no more than 100 lbs more than the C7Z. I suspect the C8 pressures will vary more from front to rear than mine do.

Bill

 

Very helpful, thank you.

For me I usually bleed down to target after first run, as you say, a bit more leisurely and ambient temps are low too- by midday track surface and ambient temps are usually much higher requiring more bleed down.

 

Thank you, very helpful. I’ll start a bit higher (26 all around?) and just bleed down after 1st session.

 

The pros say 32-34 psi is the target hot pressure.

For reference- I started at 27 psi with ambient temps in mid 70’s, sunny. Got to 32 psi immediately off track. I added some pressure and was at 34 psi. May try a bit lower pressure next time.

GM brake pads are not great. KNS offers a 2 piece rotor kit, which I’ll convert to whey GM rotors are spent. I was told to use G-Loc pads (12).

I was also told to set car to GM spec, then take rake out of the car (don’t have specifics).

I really don’t like Michelin PS4s- they are not as good as the PS2s on track (the all weather all season mission came at a cost)- they get greasy after only 1-2 hot laps. I was told the Goodyear cups are the tire of choice.

video for the curious:

 

I'm jealous... already at VIR in a C8. Interesting impressions on the PS4S... it's supposed to be better than the MPSS in every way, but I will say the MPSS was a very good tire on track; for about 3-4 hot laps, then the fronts were gone.

 

FWIW...

1. I would not remove rake from the car. You want some rake (nose down), but only a little. Taking rake away will increase front end lift.

2. G-Loc R12s are good and easy on rotors. Raced for years on Carbotech XP12/10 F/R and then G-Locs after they started the new company. It will be interesting to see if the C8 needs same compound all around due to the increased rear weight bias. I assum you're working with Ken at KNS or Wyatt at Kaizen (sp?)

3. Have you changed the fluid? Curious if it's the fluid or the pads. I've heard feedback that the OEM pads are quite good for a street pad that's still trackable.

4. What alignment do you have? I would start with GM's cold tire recommendation next. If you're on stock alignment you need to add some camber. I wouldn't go as aggressive as GM's track specs, but I'd try to get around -1.5 front and -1 rear for a good dual use alignment.

5. Were you in track? PTM? Were you shifting the car or letting it shift?

6. Have you done the track overfill for the trans yet? If not, notice anything odd?

EDIT - Watched half the video...

1. She doesn't like to turn in at rollercoaster at all.

2. General understeer when the 245s are greased.

3. I suggest trying aggressive trail braking next time out.... helps a bunch in 1 and into Rollercoaster to get the car to rotate.

What group were you running with?

 

Pros - Randy Probst/kaizen recommendation about rake, alignment, tire pressure, tire choice. I’ll trust them on that. Car was set to factory track spec, which is aggressive, I agree.

Trail braking didn’t really help, tried that in an earlier session. Cold tires were the only help. There were 1-2 laps, then fighting to not shred them, but still push a bit (Probst was doing 1 hot lap at a time). I would have preferred ambient temps in the 50s for optimum run.

Need to get on Goodyear Eagle F1 3R according to Kaizen (already ordered as set- I’m tossing the PS4s)

Brake pads had crappy initial bite, wore very fast. (The video above was session “4” with 1st session hampered bedding the brakes, 3rd session black flagged early for a mechanical problem on another car. Really on had 2+ sessions for the day). Didn’t trust pad thickness for the last session (video), only about 2mm before start of session on front pads. Kept looking for warning light, which never came on.

Traction control intervened once or twice which was aggravating despite having it turned “off.” Need to see if there is a really off setting.

I will switch to G-loc (now) and KNS rotors as soon as GM discs are done (either warp or wear out).

Red group, let the car shift (because it is that good- pains me to say. Damn near clairvoyant, just remarkable).

Yes, added trans fluid, which is a heck of a job- takes a couple hours, removing air cleaner, etc.

 

You’re saying Pobst and Kaizen are saying to take out all rake? Leave car flat? Never setup a C5 that way, but never tracked a ME car. Always tuned for the front frame slot to be 1/4” lower than the rear and then corner balance from there.




Why Goodyear’s over Pilot Sport Cup 2s?

As for all-off... in the C7 you hold the TCS button down 6 seconds until both TCS and AH lights are on. That’s everything off. Tracked a C7 a couple years and it worked... nothing was on.

 

Very nice job. Well done. Did you mention what "mode" you were in?

 

Not sure how much rake to take out (don’t have the details), but yes decrease the rake - never heard of doing that either. They say it helps getting the car to rotate- straight from Randy Probst (he also recommended lowering the car 1/2”- I can’t do that with front lift).

I was in “track.”

Thanks for tips on traction control- I tried holding it down longer, perhaps I was a bit impatient.

I thought they weren’t making PS2s anymore? Anyway- Kaizen recommended the switch. They have many, many days on them, so I’ll trust them.

 

you could go to smaller wheels.

 

I found 40 PSI is way too much hot for my driving style.

For me, 4S\Cup 2's work best in the 34 - 36 PSI.

I can feel them start to go off at 37.

<34 = low grip levels.

Out with Randy @ VIR last weekend.

 

I made 3 changes

1) dropped the rear 1.5 cm
2) Gloc brake pads
3) Good year tires

Huge, huge difference. Car turns in well. The brake feel, initial bite, modulation are night and day.

 

Was the chassis level before dropping the rear? Had mine setup and we lowered the LF 1/8”to level everything. Ended up 3.5” exact chassis to ground.

Which pads did you go with?

 

Factory track set up, then lowered rear.

Gloc 12