Autocross tuning (tire pressure, shock dampening, etc...)

[Ciotti]

What do you guys run in the way of tire pressure, shock dampening, camber, etc... for autocross?


I've been running 40 psi front and rear to keep the tires from rolling over and 2 degrees negative camber up front which makes a HUGE difference. My shocks are not adjustable and on their way out so I am picking up Tokiko D-Specs in the next few months so I'll be able to really dial the car in.



Here you can see my rear tires rolling over with 35 psi in them...

and the fronts rolling over with 35 psi...

 

[golden_eye]

Tires I run around 42 in the front and 38 in the back for a little extra traction since our cars have a tendency to oversteer. I'm running whatever the stock alignment is so with those pressures I end up with very little rolling on the front and some minor rolling on the back. The outside tread on all 4 of my tires is wearing pretty quick though, especially on the fronts.

Are you running c/c plates? Are the stock ones adjustible?

 

[Ciotti]

Stock c/c plates but the guy that does my suspension work did something to dial in 2 degrees negative camber with them. Even with that much camber I'm still wearing the outside of the tires faster but when I'm daily driving the car it wears the inside of the tires so the tire wear is acceptable.

 

[Conechaser]

Stock c/c plates but the guy that does my suspension work did something to dial in 2 degrees negative camber with them. Even with that much camber I'm still wearing the outside of the tires faster but when I'm daily driving the car it wears the inside of the tires so the tire wear is acceptable.

I would check your toe settings if you are getting a lot of tire wear.

You didn't say what tires you are running as different tires like different pressures. (street tires vs competition R tires)

I'm running 38 front and 36 rear pressures with Dunlop Direzza Z1 Star Specs on my 97 GT that I run in STX. I adjust my camber before and after each event using MM plates. My AutoX settings are -3.5 camber with a touch of toe out (1/8th total IIRC) and 5 deg positive caster. When I slide it back to the Street setting my camber is at -1.9 and a touch or toe in (1/8 again IIRC) The caster does not change.

Don't take this wrong... but it may not be the car that's the problem. The pics of the tail out slide almost indicate that it could be a problem with the steering and throttle inputs.

 

[Shadowfax]

What do you guys run in the way of tire pressure, shock dampening, camber, etc... for autocross?

Depends on a lot of different variables. I'm using Nitto 555's 275/17 on all four corners. I run the same rubber and alignment specs on the street as well as Autocross events. 41.5 psi front and 38.0 psi rear for Autocross and much softer pressure for the street. I came across these numbers by using a digital temperature gage, measuring the inside middle and and outside edges of the tire, right after a run. I did this many times until I got consistent and equal temps across the tire, by adjusting air pressure.

I get the same results simply by using chalk on the edge of the tires to see how much sidewall roll I get. There is a rubber ridge on the shoulder of the tire that I try not to roll onto. It's easy like that. Bring an air supply to the next event and play with it. What the other guy is doing won't apply to your setup. Have fun tweeking your ride.

My alignment specs are in my signature, and I never adjust between track and street because i just don't have the expertise to eyeball it. I'm happy with my tire wear.

 

[Ciotti]

I would check your toe settings if you are getting a lot of tire wear.

You didn't say what tires you are running as different tires like different pressures. (street tires vs competition R tires)

I'm running 38 front and 36 rear pressures with Dunlop Direzza Z1 Star Specs on my 97 GT that I run in STX. I adjust my camber before and after each event using MM plates. My AutoX settings are -3.5 camber with a touch of toe out (1/8th total IIRC) and 5 deg positive caster. When I slide it back to the Street setting my camber is at -1.9 and a touch or toe in (1/8 again IIRC) The caster does not change.

Don't take this wrong... but it may not be the car that's the problem. The pics of the tail out slide almost indicate that it could be a problem with the steering and throttle inputs.

I'm unfortunately running Toyo Proxes 4's for now and I'm not complaining about tire wear... As I said the tire wear is acceptable, I'm just looking for some input as to what other guys are running so that I can see how aggressive I can get with toe and camber before I cross the line and start making things worse. I don't have CC plates as they are not allowed in street prepared (I'm surprized they're allowed in STX) so I can't really dial in any caster but I think I can set a bit more camber into the factory plates. My toe is set at 0 since I daily drive the car but I'm thinking of bringing a wrench or two and dialing in a hair of toe out at the next event.

The Proxes 4's don't have a very stiff sidewall as they are considered an all season tire so I'm having to run the tire pressures up much higher than you to prevent them from rolling over. I've been using the chalk on the sidewall/tread method and it looks like 42 psi all around keeps them from rolling over. I wish I could get a set of those Dunlops but they don't make the dam things wide enough for me I'm probably going to just stick with these Toyo's for the rest of the season and then go to Falken 615's next year.