Quick Tire Pressure Question

[rock2447]

I was recently at a Drifting Competition and was talking to a guy about various car gotchas. We were discussing AutoCross and then got on the subject of wheels and tires. He has my head spinning and I need to know what psi people are running for my size tire. Here is what I have

2G GSX 17 inch wheels.
225X45R17 Kumho Ecsta Supra 712 tires.

What would be a good tire pressure?

 

[jtmcinder]

Given that you're running a lot of tire on those 6.5"-wide rims, I'd start at about 42 psi front and 38 psi rear. If the fronts are still rolling over, keep adding more to them until it just nips the triangle. If the fronts aren't rolling over, drop by 1 psi per run until you're just touching the triangles.

Once you've got the fronts worked out, you can play with the rear for balance. If it's understeering like a pig (which is to be expected), then up the rears some more. If the stars are in some freaky alignment and you're actually loose, bring the rears down 1 psi per run until it's back under control.

As to what other people are running, I can tell you, but it isn't really useful, since most people who aren't in Stock run wheels that are wide enough for their tires, have tires with much stiffer sidewalls, and have good suspensions. I run my 245/40/17 MXs on 17x8 wheels (Street Touring) at about 38/34. I run my 245/45/16 V700s on 16x8.5 wheels (SM) at about 36/33.

Be ready to have your tush handed to you. If you're in Stock or Street Prepared or SM, you'll have lots of cars on R-compounds to play with and they will kill you. If you're in Street Touring (or some regional street-tire class), it won't quite be as bad, but 712s are nothing like Azenis or MXs or KDs. So, do what you're supposed to do: focus on having fun with your car and learning to stay off the go pedal until you are unwinding the wheel from the corner. A good line is worth a lot more than speed.

- Jtoby

 

[jtmcinder]

One last thing: you seem to be somewhere between Pittsburg and State College. If that's correct, seriously consider coming to MidState Airport (Central PA Region), instead of going to Steel Cities. You'll get a lot more seat time in Central PA. Ten 45+ second runs per event, instead of something like 3.

http://scca-cpr.org/

Plus, you'll have another DSMer to talk to ... me. Don't worry: I'm only half the jerk in person that I am on the internet and I also happen to be the Novice Chair.

- Jtoby

 

[rock2447]

Thanks for the help and maybe I will be out to Central PA sometime this year. I have a lot more work to do before then. I'm doing a full suspension overhaul before I go anywhere this spring.

Again thanks for your help.