Tire pressure for 17's all the way around

[Jose Gonzalez]

I will be running some Hoosiers on a set of Grand Sport wheels. 275/40-17 front and 315/35-17 on back. Any ideas on tire pressure for autocrossing.

[DJWorm]

A lot depends on surface (asphalt or concrete) and the amount of camber you have dialed in and the ambient and track temperature.

I am assuming you will have a competition alignment done.

Hoosiers like a lot of camber, like -1.8 to -2.3 in the front and around -1.3 to -1.5 in the rear.

Our supplier has the recommendations of the top guys in class, Strelnicks and Ames for instance. The factory recommends starting at 44F/40R. One top guy likes 40F/36R the othe r likes 42F/32R

We have done skid pad work with our setup and found that the higher 44F/40R pressures turn equal results with lower pressures of 36F/32R. The mid PSI settings (40F/36R) remarkably were slower than either the higher settings or lower settings.

We prefer only a 4 psi seperation between front and back. The lower 36F/32R settings seem to give use more bite so we use them on asphalt. When running on a grippier concrette surface we will go to the higher pressures of 44F/40R.

This holds true for 275/40x17F and either the 305/30x18 rears or the 315/35x17 rears. NOTE: THE HOT SET UP RIGHT NOW IN ASP (WHERE WE MOVED TO) IS THE 305/30x18's in the front and the 315/35x17 on the rears. Again the psi settings hold true. Tire size doesn't matter as much as tire position on the car, ie. front or rear.We run a lower setting in the rear to aid traction. The 305/30x18's in the front have a smaller sidewall so there is less deflection when turning.

One other thing to note is that all these diferent tires: the stock 295/35x18, Hoosier 305/30x18 and the Hoosier 315/35x17 all have the same effective diameter at 25.5" so they are interchangeble with out affecting the speed sensing Xducer's or the speedo> Amazing. You don't have to recalibrate the computor or change the speedo gear.

[ASP_Z]

Like DJWorm said, 45-40 fronts, 35-30 rear, have gone lower but you hit a point where the grip falls off big time. The pyro does not always seem to show what the fast setup is, but is a good starting point. The 275 front might want to be on the high side, and the rears work until about 27psi - where you start looping

See you in Kansas!

[ELF Z06]

We are doing road racing. The pressures we start with(cold) is 27 front and 26 rear. Yes lots of camber. How do you guys get any real heat on such short runs?

[jknight]

Wow DJ,

From your description, auto-x setup is far from road course. To ELF Z06 question; I doubt much heat is built up, hence the high pressures to start with. Or were those hot pressures DJ?

[Dreamin]

the stock 295/35x18, Hoosier 305/30x18 and the Hoosier 315/35x17 all have the same effective diameter at 25.5"

DJ: you've posted this before: So you're saying that the Goodyear and Tirerack spec's for the stock tires is wrong - it states 26.1" diameter. It also say the fronts are 25.6"... so my fronts & rears are the same diameter ??!

JK: I think hot temps look close for road racing: I like 42F/40R hot for my hoosiers...44F works, but any higher and the tires get slippery, so 40-42F is safer. I dont watch cold pressures much as whatever I start with, I always have to let air out though-out the day as the track and air temps heat up.