Tire pressure Kumho on road circuit?

[Heysie]

I've done a trackday with the Kumho's (rear only) and the tire pressure was about 36 PSI(cold). When I look at the tire now, it looks like the middle of the tire has worn off more than the edges. Is my tire pressure to high, if so how much must it be?

 

[Tom F&L GoR]

From Lime Rock, a 1.5 mile road course, my '94, with Kuhmo Ecsta:

Cold 33 front, 28 rear
Hot 45 front, 37 rear

The pressure rise surprised me a little, but the wear was OK. All in psi.

 

[LTHL-GRY]

From Lime Rock, a 1.5 mile road course, my '94, with Kuhmo Ecsta:

Cold 33 front, 28 rear
Hot 45 front, 37 rear

The pressure rise surprised me a little, but the wear was OK. All in psi.

I had this same exact experience at Sebring this past weekend (3.7 mile course)... Lowered fronts to 40 and rears to 35(hot) to avoid excess wear. Continued to kick Slithrn's butt. I think I could beat him on just the rims.

 

[joe117]

When I used to race stock cars we would use a little temperature measuring gun to look at the temperature across the tread of the tires after a few hot laps.

With that device, you could see if the center or the edge was hot. The actual temp wasn't what we were looking for, just the part of the tire that was hot.

This was how we determined the best air pressure for the tires.

These things don't cost much. Try one.

 

[SneakyPete]

From Lime Rock, a 1.5 mile road course, my '94, with Kuhmo Ecsta:

Cold 33 front, 28 rear
Hot 45 front, 37 rear

The pressure rise surprised me a little, but the wear was OK. All in psi.

I had this same exact experience at Sebring this past weekend (3.7 mile course)... Lowered fronts to 40 and rears to 35(hot) to avoid excess wear. Continued to kick Slithrn's butt. I think I could beat him on just the rims.

32 front and 28 rear. Depending on how hard you drive, you will build extra heat and tire presure. I had to come in and drop 5 pounds out of each, to keep the car manageable.

As for LTHL-***, it funny how you drive on both sets of rims that I got you. You ran racing tires, I ran street pilots, I was 4-6 seconds slower a lap. But at morroso, I believe what ever ******** you have now will be gone, like when you accidently walked into that *** bar with the PETSN8K, the snake petter.

 

[Tom F&L GoR]

JT, I was also concerned about too high front pressures, but lowering them chewed up the edges. So I left them that high and it seemed to be what they wanted.

 

[joe117]

So,
What does the temperature cross section of the tires look like at various pressures?

How do you guys know what's going on without looking at the temperature?

 

[ViperRay]

I agree with Joe.
I have a tire pyrometer that I TRY to use.
I say TRY because you have to take the temps very quickly after you come off the track (in the pits) as the tires cool very quickly.
It helps to have a buddy help you.

A pyrometer with a probe that you stick into the tire is more accurate than the infrared type for this purpose (I've been told by people in the know).

The inside of the tire may be 10 deg. warmer or so if you have a lot of neg. camber.

 

[joe117]

The mechanics of getting someone in your pit to quickly take the reading is probably easier for left turn only stock cars.

Also, the left turn only, makes the readings easier to look at and determine what's happening.

 

[LTHL-GRY]

JT, I was also concerned about too high front pressures, but lowering them chewed up the edges. So I left them that high and it seemed to be what they wanted.

I think lowering the pressures was perhaps a knee **** on my part... I hadn't noticed any problems with the higher pressure and didn't notice any improvement or lack thereof after lowering. I never noticed any extra edge wear but my set is pretty much gone.

Maybe it had more to do with worrying about having to drive 3.5 hours home on them after the event

On another note, I had my front rotors turned and a new set of B3's installed and the brake shop reverse mounted the wheels (counter to rotation arrow). I didn't notice until half way there Sat night. This actually helped as the inside half of the tires were almost slicks-with-grooves while the outside still had a little tread left. This effectivley relocated the remaining tread to where the wear was (say that 3 times real fast)... I wouldn't necessarily do it on purpose but in this case it was OK and seemed to put the extra traction where I needed it.

It was my best track day yet in terms of performance and whipping up on Z06's and little garter snakes like Jay.

 

[Heysie]

Thank you, I will lower the tire pressure.

 

[joe117]

JT,
Do you get more traction on a road course when you have tread on your tires?

 

[LTHL-GRY]

Joe,
No, I wouldn't think so, although my limited experience is based on Pilots last season and Kumhos this year. As I have to drive a substantial distance to and from the tracks (3.5 - 5 hrs one way) I felt better having what little tread was left where the wear had accelerated. The Kumhos seemed to perform better the "slicker" they got. Again, I am new at this (10-12 track days) so its seat of the pants, or maybe I have improved a little...

The ACR shocks and springs I just put on may have helped too

 

[joe117]

"relocated the remaining tread to where the wear was"
"seemed to put the extra traction where I needed it."

I didn't know what you were talking about.

All that aside, I have the Kuhmo Ecstas. They are sticky tires. Every Viper should have them.
But not in the rain.

 

[LTHL-GRY]

"relocated the remaining tread to where the wear was"
"seemed to put the extra traction where I needed it."

I didn't know what you were talking about.

Clear as mud to me.

All that aside, I have the Kuhmo Ecstas. They are sticky tires. Every Viper should have them.
But not in the rain.

I agree. We got caught once in the rain on the way to the track and had to straddle the lanes to keep from hydroplaning in the ruts. You learn real quick to leave lots of room between/around the cars...