View Full Version : Race alignment-tire pressures?

03-25-2006, 06:53 AM
I race with a group of amateurs and vintage racers and everyone seems to have his own idea about tires and alignment. The tire companies only provide very general info on this. I've read varous books and articles on this stuff too.
Over the years, I've tried to set up my cars in a fashion that seems sensible in terms of tires and alignment.
Like most British sports cars, mine is front-engine, rear wheel drive.
I am using Yoko A032R (soft) or Kumho Ecxsta V700s (shaved DOT/race tires) that are 175-60-13 (a pretty modest size partly due to the fact that I am running stock steel wheels).

Here's my question:

I run around 36 to 38 psi HOT in my tires, I run about 3 degrees of negative camber in the front end and I am using about 0 to 1/32 inch of toe-in on the front end.
How does this compare to some of you other fellows?
I realize that different types of cars will have different setups, so I know this stuff isn't directly comparable. Still, I think it's useful to compare.
Caster is stock and bump steer is about as good as I can get it.

Simon TR4a
03-25-2006, 10:55 AM
I have tried a couple of things in Solo 1; the first theory being that when you get off the track the pressures should be about equal in all tyres, which led to putting more air in the back than the front and more air in the right side than the left because most (roadrace) tracks are run clockwise so the left front heats up the most as it does most work. Most people say you should gain 4 psi between cold and hot but I would get 6 in the left front, and as little as 2 in the right rear!

Later I tried measuring tyre temps (all 12) with a probe type tester you stick into the tread, not a surface pyrometer, but as we do a cool-down lap after the 3 timed laps I was never confident of representative readings and they usually were too low, around 130-160, surface temps on the track should be in the 200 range.

So the final theory was start at 34psi front and back, increase the front if it wouldn't grip, and concentrate on learning to drive better.
I was using the hard compound 032R as I drove to the track,(they make great rain tyres!), 205/50/15, 2 degrees negative camber front, 1 degree negative rear with my weight in the car, no toe-in front or back. Caster is not adjustable on my car.

I imagine the sizes of the wheels and tyres would be proportional to the weights of the cars roughly speaking, but as most of the guys run front drive or large V8s I just tried to figure it out for myself; not saying this is the best way to go.Simon.

03-25-2006, 12:18 PM
Hoosier 20 x 8 x 13 slicks on a 1577 lb. Sprite. Running 1.75 to 2 degrees negative camber, and cold pressures of 20.5 on all four. I like to see about 25psi hot. I run 1/16" total toe in, and this setup seems to work for me.
When I was running the Spit, the setup was basically the same.
As far as temps go, I just shoot for trying to equalize them across the tire, and get everything as close to identical as I practically can. I tend to run a fairly "hot" cool down lap to keep the temps in the tires up.

03-31-2006, 11:40 PM
Get a book on suspension/allignment setup. I don't have mine in front of me so won't qoute the details but what you seek is even tire temps across the tire and on both side tires. If the inside is hotter (more wear) either the toe is off or the camber is too much. Vice versa.

For most AXers, adjusting during an event is hard, unlikely, impossible, etc. On most short AX courses, tire temps may not get up to a good sticky level anyway.

Track days and racing events and multi lap events are more likely to get tires properly hot.