Kentetsu

Hi guys,

Just made the move up to some Hankook race tires, and am looking for some advice on starting air pressures.

I used them this weekend for the first time, and I have to say I am very impressed. I usually don't have much trouble winning my class (CSP), but this weekend I was duking it out with the SM guys for FTD. I actually managed to win FTD on Friday, beating out a highly modified '02 Vette by .5 seconds.

For the first race, I left them at 28 psi (which is what the shop inflated them to). It seemed to work very well, but I was concerned that they might have been underinflated. The next day I started out at 35 psi, but I don't think they did quite as well.

I understand that the proper way to do this is with a thermometer, checking the tire temps after a run. However, I don't have a fancy thermometer, and usually run short on time anyway. So, for now, I'm just looking for ballpark figures to start out with.

Anyway, the car is an '85 GS running 225/45/13 tires on 13x8" rims. The cars weighs about 2280 with me in it and race ready. Any advice on starting pressures would be greatly appreciated.

Here's a quick video of my winning run (I got a little excited after trying all afternoon to catch that Vette). My run was the very last run for anyobody that day, so kinda like the cherry on top if you know what I mean.

http://www.youtube.com/watch?v=i_pVYnbxkzk






.

Brent Dalton

iTrader: (31)

bracket your pressure. You've tried 28 and 35, next try 32. From there, go up or down until you feel it's optimal. A good way to judge if it's under inflated is to look at where the contact patch and sidewall meet and see if the tire is "rolling over" or if there are signs of wear past the outer edge of the tire.

FWIW, I think 30-32 is what I normally see ppl at the AutoX run on Hoosiers. I start significantly lower than that, but I would guess their hot pressure and mine are about the same.

j9fd3s

iTrader: (3)

we road raced em, so its going to be a little different, but we were starting around 26-27psi, and shooting for 34ish hot.

however brent's procedure sounds good too.

jkstill

iTrader: (11)

+1

When I first got DOT rubber, I started at 35 psi and dropped until they felt good.

After more experimentation I generally like them at 28 front, 27 rear.

These are 285/18/30, Hoosier A6 and Kumho V710.

Temps tend to be fairly even at +-20f across the tire, though they will be better whenever I can get some more front camber in the FD, as the inside of the tire is still tending to be a higher temp than the outside.

mazdaspeedrex

Get some tire chalk and mark across the full tread width of the tire. After your run if there is any chalk still showing you can drop pressures. I run Kumho V710 215/50R13 at 35 front and 30 rear, but I think you have more front camber than me with your coilovers. I can only get -1.2 before the springs hit. I don't touch the inner 3/4in of tread on mine.

fd_neal

iTrader: (4)

I run 710's on the roadcourse so its a little different but I used to run ~30psi hot because it "felt" the best, but after playing with pressures for a half season I now run 34psi because it picks up about .5 second per lap. Also I have pyrometer data that shows an even temperature trend from 28psi up to 35ish psi so that didnt really help me in fine tuning pressures. Solo2 is harder because you cant run lap after lap collecting data to make the minor tweaks... If you have a local racer that you can consistently battle with that might be the best way to dial them in.
I know im a different tire in a different application but my point is what feels best isnt always fastest.

Kentetsu

Thanks guys. Lots of good advice. I didn't use chalk this time, but it appeared that the tires were wearing evenly at 28 psi and 34 psi. I'll keep working at it.

jswisc

iTrader: (1)

Hankook recommends 40 PSI hot. I had R6 Hoosiers and ran at 29 hot. I run the same tires as you and I run 36 cold and that gives me 40 coming off the track. Love the tires. Ready for my next set.

Brent Dalton

iTrader: (31)

Hoosier recommends the same(39 hot), but I have found that to be less than optimal for my application. So many factors play into the equation though.... alignment, driver style, rest of the car set up, etc...

Kentetsu

I ran at 28 again today at the Porsche club's autocross. Felt good, took ftd.


http://www.youtube.com/watch?v=-RfRymkOXS8

Brent Dalton

iTrader: (31)

woot woot! congrats!