V4kerker

I have a '07 c6 coupe auto with FS wide oval run flats. I've got a HPDE at summit point main this Friday. This will be my 2nd time HPDE and first time on cold tires and cold track. Back in Oct 65 degree day. I ran my tires at 30psig front and rear with a 6 to 7 psig increase after a 20 minute session pushing myself/car to about 50%.

I'd like to know which way to adjust tire pressures after my first or 2nd session depending on how the car is reacting to road and tire grip.

Thanks for any help.

VetteDrmr

If you were happy with your pressures on your previous event I'd leave them alone. Grip will be down due both to the track and tire temps, and I don't know how much tire pressure will really make a difference.

On street tires I'm more concerned about keeping the tires healthy, rather than finding optimum grip.

HTH, and have a good one,
Mike

longdaddy

start with slightly higher pressures as they may not come up as fast on a colder day. if you can keep street tires with street alignment in 37-38 psi range hot, and still be comfortable with the grip, you'll be OK. do keep in mind that you will be much faster on your second day compared to your first day (if that was your first ever day on the track), so your tires may behave differently.

As Mike said, your first priority is not punishing your tires more than you have to, so watch the tread surface for the evidence of overheating/stress. It usually starts with "leading" edges of tread blocks looking frayed and getting what looks like small dents/holes, especially around the outer edge. If that happens, your immediate options are to call it a day, add more pressure to take the load off the outer edge (and suffer reduced traction), run shorter sessions to avoid building up too much heat, or keep driving until your tread rubber starts to actually separate from the rest of the tire, then go home on a flatbed. Most people to whom I talk about it on the track after seeing first signs, tend to opt for the last option.
If I am on the tires that cannot take the heat I am putting into them, I usually just run shorter sessions. I do not like loading my car onto the tow truck, going home early, or having to slow down for my tires.

in all fairness, you will probably be OK if this is your 2nd event. as long as you pay attention to hot pressures staying in the range that's comfortable to you, and tread surface looking reasonably healthy, you should be fine.

travisnd

I always tell my students they want a street tire around 40psi hot. As mentioned, on a cold day they won't come up as much. For a powerful RWD car I'd start around 33 front and 32 rear +/- a pound as needed.

If you're C6 has TPMS then you can monitor real time when they're at their hottest. After you cool down and come in you can check them. If they're over 40 psi I'd bleed them down to 40 and then let it ride.

sothpaw2

I'd guess 31-32 also. Tomorrow's supposed to be 47 F high. Maybe you'll get a 5-6 deg rise during session. It will be different morning vs afternoon...plan accordingly.

What do you guys think about grip in 47F but sunny weather? I was guessing that the coldest I'd want for optimal grip would be 50's, preferrably mid-50's. Saw that in Oct; 52 cloudy not nearly as fast as 65 and partly cloudy.

V4kerker

Thanks for you imput guys. I'm think I'm going to just leave the tire pressure at 30psig for the 4 20 minute sessions if my driving skills keep improving each session. I'll take cold and hot pressure readings each session to have some base line numbers to go by for future runs.

I really need to work on my driving skills brake,steering and gas inputs instead of making changes to the car.We your imput I at least have some kind of direction to go if things get to loose. This will be my 2nd every HPDE I'm actually looking forward to a cold track so it will bring out my driving flaws. Hopefully with no off track fun.

longdaddy

if the track is dry, it does not make as much difference as most people think, as long as you can bring the tires to their optimal temps - that would take longer than usual, but as long as you are careful on the warmup laps, it's fine.

I have done days with first session or two at near or even below freezing temps and it was not a problem as I could get the tires to the temps where they would work well enough to start pushing the car within a couple of laps

now, if you are doing something like autocross, where the temps you start with is pretty much what you get, the difference can be huge.

V4kerker

Just got back from my second every track day. The temp for the day pretty much stayed around 40-45F for the day. I started out with 32psig all 4 tires. At the end of First session tire pressures were 36 and the 4th session I saw 39. I never really pushed the car hard enough to have any real tire issues until maybe my 4th session.
The 4th session I picked up the speed and started braking harder and with about 2 laps left my brake fluid boiled I've never had that kind of experience at 100+ mph going into turn 1 at summit point main. I guess it's time to flush the fluid again.

travisnd

You sure the fluid boiled? What happened? My guess is you probably got the pads hot enough that they started to fade vs. actually boiling the fluid.

1ED1

Did the brakes go to the floor or was it just hard to stop?

V4kerker

The paddle went to the floor. I was able to pump the paddle and get some firmness back in the paddle.

Is brake fade when the paddle is still firm but the car doesn't stop as good?

naschmitz

+1
Stock pads will fade way before the fluid boils.

VetteDrmr

Yes. Sounds like you either boiled the fluid or perhaps tapered the pads. If the latter then you'll notice a long pedal (but firm) that will stop the car normally. The pedal will gradually come up to its normal spot as street use trues the pads back up.

Sounds like you had a good time, excellent!

Have a good one,
Mike