Hoosier Tire Pressure for the track

[DPassell]

I just bought a new set of Hoosiers, 305/30-18 f and 335/30-18r on a set of CCW wheels. I'm running a DE at Roebling Road this weekend with the local BMW club, and would appreciate any advice on tire pressures specific to the Hoosiers. I know they like higher numbers than the F1's, but I figured someone on the forum would have some good numbers from experience. The CCW wheels are great, BTW.
Don P
02 QS

[Subdriver]

I think if you start at 34 front 32 rear you will be close. I try for 38-40 hot, but only have two days on the Hoosiers so haven't had much time to play with this.
Here is some info from tire rack:
http://www.tirerack.com/tires/tirete...n/racepres.htm

Have a great time there. I did that event last year and had a blast. Well run event.

JOEZ06,
You going to this one? Looks like another Jax Z06 running mate. Damn I can't wait to get my car back!!!

[DJWorm]

Hoosiers like more negative camber and more pressure. We usually run a 4 psi difference front to rear

My starting point recommendation would be 40/36. I know for a fact that some of the National Champs run these pressures.

We did skid pad testing and found that 44/40 was as fast (the same) as 36/32 and both settings were faster than the 40/36 on our car. We now use the 36/32 for asphalt and 44/40 for grippier concrete.

We also found in our last race on concrete than none of our testing held fast and we ended up running 38/32 but on concrete that was hot and somewhay slippery in places, So....yau have to adjust to track conditions.

These of course are cold starting pressures ....and we continually check after each set of runs or laps. The tires of course will build pressure and we bleed down to the starting pressure just before going back out for the next series.

We also monitor tire temps religiously and that is what we base our pressure adjustments on in addition to what the car is doing and what we want it to do. Optimally we try for no more than an even 10 degree spred across the face of the tread. inside being hotter. This also tells us if the tire is over inflated or under inflated.

[Subdriver]

DJ,
I think you are referring to Auto-x aren't you? He is asking about tire pressures for extended sessions on a road course. In my limited experience, you will see about 6-8 psi increase at Roebling from "cold" to "hot."
If you start at 34 front 32 rear I think you will find yourself near 40 front 38 rear when you come in off the track. That depends a lot on how hard you drive, what your negative camber is, and the moisture content of the air you put in the tires.

[DJWorm]

I am talking about both. Our tire set up and pressures are not to different between AutoX and the track surprisingly. We do change our suspension somewhat for the track (less negative camber and toe in in the rear but not much). If we are running long and hot lapping sessions we will maybe drop the starting pressures somewhat, maybe 1-2 degrees but the car really doesn't handle well and the tires do not grip well until the tires get to temp.

We also have just started running custom pressure relief valves on hot days to limit tire pressures and automatically bleed the excess pressure.

We also use compressed straight N2 in the tires. We do not fill with air. We are also going to experiment with CO2 this season.

We feel the compressed N2 has less to no water content and is much more stable and with less temperature rise.

There have been days when the car was fastest at the Glen which is a relatively high speed course, with a starting pressure of 44/40. It all depends. There have been a few days when we couldn't get rear traction until we were running 21 #'s in the rears. Rare but it has happened.

[Dave]

A bit off subject but what offset do you use to run 17-11 wheels on rear of Z06?

[DJWorm]

I am talking about both. Our tire set up and pressures are not to different between AutoX and the track surprisingly. We do change our suspension somewhat for the track (less negative camber and toe in in the rear but not much). If we are running long and hot lapping sessions we will maybe drop the starting pressures somewhat, maybe 1-2 degrees but the car really doesn't handle well and the tires do not grip well until the tires get to temp.

We also have just started running custom pressure relief valves on hot days to limit tire pressures and automatically bleed the excess pressure.

We also use compressed straight N2 in the tires. We do not fill with air. We are also going to experiment with CO2 this season.

We feel the compressed N2 has less to no water content and is much more stable and with less temperature rise.

There have been days when the car was fastest at the Glen which is a relatively high speed course, with a starting pressure of 44/40. It all depends. There have been a few days when we couldn't get rear traction until we were running 21 #'s in the rears. Rare but it has happened.

[jrz1]

Definitely heed the advice on more negative camber - especially at Roebling. If not, you'll experience rapid, premature wear on the outer edges, especially the left side.

[Subdriver]

DJ,
Since you are using N2 and a max pressure bleeder, I think your numbers might be a little misleading to most of us poor guys who use air, especially the really poor guys down there in Florida who have to use really hot sticky humid air.
Your numbers probably reflect a good hot pressure to shoot for.

A bit off subject but what offset do you use to run 17-11 wheels on rear of Z06?

Dave,
I should know this, but don't. I bought my CCWs from Tom Reichel at:
http://www.midatlanticmotorsport.com/
I trusted him to get the right size and he did. They fit great.

[DPassell]

Thanks much for the info guys, you gave me some good numbers to start with. I'm running -2.0 neg camber in front and -1.0neg in rear. I know the Hoosiers would like more, but I don't want it to be too unfriendly on the street with the F-1's. DJ, speaking of temp guns, any preference on the Laser models vs. the needle type that touches the tire. The laser seems easier to use and I am thinking about the 200 buck Rayteck(sp?) model.

Subdriver, Joe couldn't make it this weekend, had to go to San Fran for work. We went to the Chin DE last month together and he told me about you. We are going to do more events soon, so come on down and join us.
Don P

[DJWorm]

The CCW's have the max. allowable SCCA + offset built in: +0.25" plus you may need to run a 1/16" or 1/8" hub centric aluminum hub spacer. It's not so much tire clearance but the end of the spring perch can rub on the inner rim crown especially under compression during hard acceleration and cornering. You will notice small shards of aluminum shavings all over the track!!

No those are my cold starting pressures ....you need to bleed back to those same pressures as the tire heats up. You check tire temps just after coming off the track. You check the tire pressures and adjust accordingly in grid just before the next lapping session. The tires should still be hot and usually you will have to bleed off some psi. We do this to get back to the cold starting temps even though the tire is hot and in consideration of the tire temp readings. The tire temp readings tell us if we need to change the starting pressures for the next lapping session. It's imperative to check those temps again and make further adjustments if necessary. The real benefit comes when you check your note book (you were writing all those numbers down right?) before the next event and you can set those pressueres and forget about it, only bleeding hot in the grid to get back to the optimal pressures you established before.

I do not like the guns....i do not think they are that accurate and there are too many variables. I use the Longacre probe with memory. I can store inside middle and outside tire temps for each tire x 10! This allows me to recall and compare settings and really dial in the pressures.

HINT: Once you start the proceedure do not make any starting pressure changes greater than 2 degrees at a time.

4 neat things we have in the pits
1. Longacre Memory Pyrometer
2. Longacre tire Pressure Guage
3. Pair of rubberized work gloves to clean off the tires
4. Small portable N2 tank.

[ghoffman]

For road racing it should be 42-44 HOT, 38 is too low for Hoosiers. What ever that means cold, is up to you to decide, about 34 cold front, maybe 36 rear. The fronts will rise more due to brake heating so adjust accordingly. At tracks like LRP, we run different cold pressures on one side to compensate for the mainly all RH turns.
The biggest advantage of N2 is the lack of moisture, (PV=nRT for all gasses). If you are going to run Penske, JRZ, Moton, etc shocks you will need to check the shock pressure anyway so it is a good idea to get N2 cylinder and regulator anyway and use it in your tires. A good second choice is dry air, go to Home Depot and get a moisture separator.
I agree with the IR gun statement. The problem with IR guns is that they only measure surface temps. The probe type is a better indicator of the real tire temp.

[JOEZ06]

Don/Brad (Subdriver)

Yeah, we have hooked up before. And many more to come....!!!

What a nightmare--a red eye return this morning in bad weather... I finished my meetings by 2pm and then I was STUCK ... SJO and SFO had nothing coming back until 10:30pm... I had thoughts of getting back early enough and showing up to see if they had room.

I am shooting for a PCA event in mid April (@RR) and May at Sebring with Chin.

Don-- let us know how the weekend went...!!! How was the weather? Any rain? If so, wondering if you ran the Hoosiers or the F1s did in the wet ?

[DavidBest]

I was DPassel's instructor at Roebling. Excellent driver, especially after only 2 schools. Moved to A group (fastest next to instructor) on Sunday. Fastest car in the group. He was as fast as me (of course, he was on big fat sticky Hoosiers and I was on F1s). The Hoosiers stuck like glue. Tire wear wasn't too bad, but it was cool (Sunday in the 50/60s). Oil still got hot.

[Subdriver]

Don, David,
Glad to hear it went well. Argghhh. I can't wait to get back on the track...
So, inquiring minds want to know. What pressure did you end up running cold/hot and how did it feel?