Track tire pressures (track tires)

[MetalSpikeRacing]

I though I make thread about tire pressures at the track, while on track tires.

This will help to understand better the behavior of our cars under diferent set ups, by knowing what have worked for others.

I'll go first :
Tires Dunlop star specs.

Front 235-40-17, pressure 40psi hot

Rear 275-35-18 , pressure 38psi hot

Comments: I could of probably dropped a psi or two at the back to push a little harder out the corners, probably next time.

-MSR

 

[Greg-TT]

For me, 36 front and 38 rear hot worked best on star spec Z II tires.

 

[imranman]

noob question alert: How do you set your tire pressure at their 'hot' settings when your tires are cold their first run? Do you set them to standard settings, go out, then adjust them hot when you get off the track?

 

[CL65 Captain]

noob question alert: How do you set your tire pressure at their 'hot' settings when your tires are cold their first run? Do you set them to standard settings, go out, then adjust them hot when you get off the track?

yes. It depends on ambient temp, track surface, and how hard you drive etc. But set them somewhere around 30-32 and when you come back in check them (this is the "hot temp") and adjust up or down from there. You should see a bump in pressure of somewhere around 4-6 lbs. Periodically check them through out the day as they will probably rise in the afternoon as the ambient temp rises and bleed them back down to whatever your target is - for me - 36F/38R.

Because air has water vapor and oxygen as the tire heats up from the friction, the pressure rises. This is why race teams use Nitrogen only in their tires as it has less of a change in pressure when the tire heats up. Same reason why we use Nitrogen in the tires of jets but because of the extreme temp changes (-50c at altitude).

 

[Honcho]

42 front and 42 rear hot worked great for my Yokohama s.drives (215/40/17; 255/40/17). Even my instructors were suprised something so high felt so connected. We kept debating whether to let some air out, but the car was just hooked up, so we left it alone. My next track day I am going to try 39/39.

 

[docjohn]

it is generally accepted that the Ra1 works best between 37-39 psi hot.

 

[imranman]

Thanks CL65. Any recommendations on tire pressures to try? (I know everyone has a different flavor). I have Dunlop Z2 in 215/40/17 and 265/35/18. Should I give your 36-38 HOT a whirl? I've been autocrossing this year and the general consensus from the people there was to up the tire pressure which is what I did cold, but the car felt a bit skittish (I was running 38/40 COLD).

 

[g3driver]

I use the z2 and I like 32 hot all around. I you look at the tire wear markers on the sidewall you will see 40 hot is way to much pressure. Look for the triangle on the sidewall and scrub the tip of it for optimal pressure (thanx coz) for pointing that out!

 

[CL65 Captain]

Thanks CL65. Any recommendations on tire pressures to try? (I know everyone has a different flavor). I have Dunlop Z2 in 215/40/17 and 265/35/18. Should I give your 36-38 HOT a whirl? I've been autocrossing this year and the general consensus from the people there was to up the tire pressure which is what I did cold, but the car felt a bit skittish (I was running 38/40 COLD).

There are too many variables which is why everyone has their favorites. Autocrossing is going to be different than road course as autocross is usually under a minute and the track is 20-30 minutes.
The ballpark is 36-38 hot either front or rear or both. But it's subjective as what feels good to you. I might like it setup differently.

The BEST way is to use a pyrometer.... temps don't lie.

 

[docjohn]

The BEST way is to use a pyrometer.... temps don't lie.

thats it ...looking at scrub marks is vague at best...even temps across the tire tell you much more about pressure and alignment.

 

[illwillem]

The most optimum situation is to adjust tire pressures individually per tire based on sidewall scrub and temps you get from certain characteristics of the track, SOW CCW or big willow have really heavily banked bowls or long brutal turns that really works the front right. I'll start out even side to side for the first session but always end up letting 1- 2lbs or adding pressure in response to the temps and sidewall scrubbing i see after warm up. I wouldn't very more than maybe 3psi psi side to side but it helps. Ideally this type of track specific scrub would be fixed more functionally by adjusting camber and toe which is a PITA but Ive found there is some helpful adjustment in tire pressure. 90% of the time or for auto cross youll be fine with even.

 

[CL65 Captain]

In a theoretical world you would want temps around 200F-220F all the way across. But toe will cause the inside to heat up going down the straight, etc. So ignoring that variable you would "optimally" want 210 210 210.
For example - 210 230 210 would indicate too much pressure. 230 210 210 would indicate not enough as the tire is rolling on the outside edge and raising the temp. But as I said, there are a lot of variables and you won't ever get the same all the way across. But you use it as a guide when you see one that is out of whack.

 

[docjohn]

Thats how I figured out i had worn front tie rod ends..outside temps were too hot despite optimal pressures for that track....And yes the rear tires will run hotter on the inner third because of toe in.

 

[stuntman]

Its commonly accepted to have the inside of the tire 20*F higher than the outside ex: 190-200-210 210-200-190

 

[nsxalot]

Thanks, Billy

Its commonly accepted to have the inside of the tire 20*F higher than the outside ex: 190-200-210 210-200-190

- - - Updated - - -

What makes the inside part of the tire get hotter? I would think the outside of the tire would be taking on more of the pressure and weight of the turns. And that is what would makes the different happen.

Lance

 

[stuntman]

If your contact patch is sufficiently cambered (where the tire is used evenly across the tire) when cornering hard at the limit, it will be cambered and increase inside tire temps during braking, light cornering, and straight-line driving. If you are getting even tire temps across the tire when you check them in the pits, you are probably burning up the outer edge of the tire and not loading the entire footprint of the tire evenly when cornering.

20* hotter on the inside is commonly accepted for a modern radial r-comp, street tire, race tire, etc... Bias ply tires or super wide race tires may require more or less. Stick to 20*.

 

[imranman]

Thanks guys this is valuable info. I'm going to test out 36/38 psi HOT next time out and go from there. Hopefully it'll bump me up the ranks!