Direzza Tire Pressure for Autox

[timhatimay]

Hey everyone,

I just got some Direzza's installed for this season, and I'm really excited to use them on the auto-x. I'm just curious what kind of tire pressures everyone is using for auto-x. My last tires were Hancooks, and I always had to run around 40 psi to keep them from rolling over too much. It seems the Dunlops are much more firm and I think that will be less of a problem. I know some chalk and/or experience is the best method, but I'd just like a starting point!

Thanks!

Tim

[aisthetes]

I had success with 41 F / 39 R hot temps. You definitely want the pressures higher than you would for a road course due to the single lapping format of an autocross where you don't get time to build up temps. The quicker, tighter turns also call for higher than normal racing pressures to keep the tires from rolling over in turns. Without camber plates, the Star Specs still wore the outside edges regardless of pressure, though.

[Xaeryan]

My preferred pressures for Z1s are similar - 40 front, 41/42 rear. I use rear bias to aid in rotation - I find with extra pressure in the rear and a little braking on corner entry to unload the rears, the rear slides a bit, pointing me into the corner.
So I always trail brake into tight corners.

[timhatimay]

Thanks for the input guys. I should have mentioned, it won't be my first auto-x just first on the new tires. Also, I have the BMW PS, M3 front arms, M3 sway bar, and Dinan Camber Plates (currently running -2.0*). I still expect to roll some, but shouldn't be quite as bad as stock!

Last year with the Hankooks, I went back and forth between the two philosophies you seem to have. Some times I ran a few psi additional in the rear to get some increased rotation, and sometimes I kept it a bit lower in the rear it seemed to make the car very balanced with good rear traction. I think I was a bit faster with the former, but I felt like I was fighting the whole course to keep my car straight(ish). Looks like I'll be running similar tire pressure after all, or at least starting there. I'll probably start somewhere around 39 f/r and go up or down from there. Thanks again!

Tim

[Amalfitano]

Last year I found the best combo to be 40f/38r for the cold start with 80 to 90 degree days, and if i wasn't overdriving i wouldn't even need to bleed off pressure, it would nicely climb to 41/39 and stay there. I liked the sensation of more pressure in the rear, but my times weren't improving, so i stayed with what i was getting to work (which isn't to say that the times couldn't get reached with the higher pressure rears, i just wasn't able to get there quickly).

Right now, i'm finding with the wider rubber and a more proper suspension setup that the pressures need to drop. To be fair it was only 60 degrees out and a bumpy gravelly surface, but i started at 36 square, wasn't rolling the front and the rear was still a bit skatey, so i kept it hot 37f and dropped the rear to hot 35.5. I was able to control the rear a little better, but i'm not sure i'm getting to the right pressure yet with a 255f/275r

[Lubo]

It depends on the tire size as well. For example last year I ran on stock 18s with 225f 255r. I needed 36-38 cold pressure to prevent scrubbing of sidewall. This time around I am running 255/40 17 and starting with 32psi cold without any rollover. It is definitely something you need to play around with.

[timhatimay]

An update: I started off at 39psi front and rear today (warmish tire temp), and played around. For this particular course, I found that 39 front and 40 rear was working very well for me. The Direzza's have a really great feel and lots of traction. Quite a bit more predictable and sticky than the Hankooks, so I think I need to adjust my driving a bit to compensate. Thanks for the advice everyone, now that I have my starting point I'll continue to tinker until I'm satisfied.

Thanks!

Tim

BTW - Tires are 225/45-17 and 245/40-17

[gotcone.com]

Originally Posted by Amalfitano

Last year I found the best combo to be 40f/38r for the cold start with 80 to 90 degree days, and if i wasn't overdriving i wouldn't even need to bleed off pressure, it would nicely climb to 41/39 and stay there. I liked the sensation of more pressure in the rear, but my times weren't improving, so i stayed with what i was getting to work (which isn't to say that the times couldn't get reached with the higher pressure rears, i just wasn't able to get there quickly).

Right now, i'm finding with the wider rubber and a more proper suspension setup that the pressures need to drop. To be fair it was only 60 degrees out and a bumpy gravelly surface, but i started at 36 square, wasn't rolling the front and the rear was still a bit skatey, so i kept it hot 37f and dropped the rear to hot 35.5. I was able to control the rear a little better, but i'm not sure i'm getting to the right pressure yet with a 255f/275r

With the 255/275 set up I usually run 38f / 36r on a concrete smooth grippy surface. It varies from surface to surface and your driving style, so you kind of have to just feel it out somewhat.

[larryn]

Originally Posted by gotcone.com

With the 255/275 set up I usually run 38f / 36r on a concrete smooth grippy surface. It varies from surface to surface and your driving style, so you kind of have to just feel it out somewhat.

This is nearly exactly what i did, with that same tire size. I found 37F/35R was my sweet spot.