Tire Pressures - What do YOU run?

[that_guy]

Just ran an event on the weekend and while I've played with pressures a little at each event, I figured it might be a good idea to get some other options to trial while out there. And who better to get it from than other autocrossin' twins.

Here's my setup and go-to pressure settings at events...

17x9 RPF1 with 245/40R17 Dunlop Z2's
KW V3's (settings determined by track layout, but basically low compression/high rebound front, opposite rear)
-2.2 camber front, -2.4 camber rear
0.4 total toe in rear, 0 front toe
40psi square

So far it's been working, but I'm falling back a little in STX against new competitors and I'm trying to find that edge. I started the season with an event at Mosport DDT (Ontario, Canada) that gave me a good setup for going forward this season. Basically was fastest car of the day on the track out of all participants in Advanced driving group, so a good setup indeed.

Moving to autocross, I've placed 1st, 1st, 2nd, and recently 3rd in class, with positions of 6th, 5th, 5th, and 7th overall, respectfully on PAX at each event (out of 65-75 cars per event).

Video from event 1 this season:
[ame="http://www.youtube.com/watch?v=AydZC-DPVws"]2013 Scion FR-S - TLMC Autocross - June 23, 2013 - Run 6 - YouTube[/ame]


Car lacks brakes, which I have in a box waiting for install and a few other things that can be fixed with parts I have at home for it. But the pressures thing just seems like an easy experiment. That and I figured it might benefit others to know what to run as a base map for when they try to setup their cars in the future.

So...what do you guys run and how well does it work for you?

[zohaib]

We tuned tire pressures this whole weekend at autox's, with multiple drivers switching back and forth on the same car to test and benchmark. We started with 40psi all around, and went up or down 1psi every run (did around 30 runs on Saturday and 15 Sunday). I have the stock factory tires on the car, and with the ambient temperature being around 80, on resurfaced asphalt, we discovered that that the optimal pressures was 41f/36r. We'd have to let the air out after every run because the heat was building up quick on the tires, but if we went higher than 36psi in the back it became too loose (almost icy), and anything under made it more difficult to throttle out of corners. We expected to go less on the front but with the tighter turns on the courses we were running the sidewalls too much. On a track day I'd predict 39psi in the front may work better.

But then again, all this will go out the window once we swap tires, so there's that...

[Stevo22]

At my last event (on stock tires) I started with 40/40 then bled down to 36psi front and 38psi rear. This seemed to be working for me. The rear end would step out so I could wiggle it around cones and you could see my scrub like right at the sidewall but not into it.

Note I am an amateur at auto-X.

[that_guy]

^I'm seeing even wear at 40psi and am comfortable with it's twitchy-ness. I might try bumping the rear a point or two though to help through some of the tight bits.

Keep the input coming. Good to see my rates were not far off others.

[mla163]

The best way to establish proper tire pressures is with a probe type pyrometer. Ideally you maintain constant temp across the entire tire. If the middle of the tire is too cold - more air. If the middle is too hot, less air. If the inside is too cold, more camber. And so on.

Different tires and different setups will require different pressures.

[xwd]

I used 33/32 in my rivals and liked the car with that pressure, but they seem to like low pressures. This is 225/45/17 on 17x7 rims.

[RehabJeff86]

Originally Posted by dwx

I used 33/32 in my rivals and liked the car with that pressure, but they seem to like low pressures. This is 225/45/17 on 17x7 rims.

Wish i had seen this earlier, had to learned the hard way this past weekend at MRLS.

Started with cold 37psi front and 36psi rear -- not a good idea, lost it Turn 9

Lower to cold 34 psi all around -- much better, turned into hot 39psi all around

I agreed cold 32-33 psi will be ideal for Rival 225/45/17 and this is what i will use next time out. :happy0180:

[TRev]

Z2's I run 38 front and 35 rear (at full temp)
Rivals I run 32 front and rear (at full temp)

Some prefer to run the Z2's at lower pressure. I didn't like the way they felt as they seem more lethargic to me. You might want to run closer to 40 if you are lacking negative camber up front. Just keep an eye on the triangle wear on the outside edge of the tire.

[feldy]

With 17x9s and 245/40/17 rs3s I run 28 29 front and 26 rear.

[canu_50]

re-11 235/40R17 on a 17x8, Brought those to 34-36 hot. Over that my car was loosing stability on acceleration and rear end was a little bit more twitchy!

[jonesy]

225/45R17 ZIIs on stock wheels, running 35F/33R

[that_guy]

Interesting with the variety of pressures. It seems that a lot of you like the lower pressures.

I may have to try this. Car doesn't feel bad with 35psi or 40psi really. Wonder what 32 would be like? Might have to try at the next event!

Originally Posted by mla163

The best way to establish proper tire pressures is with a probe type pyrometer. Ideally you maintain constant temp across the entire tire. If the middle of the tire is too cold - more air. If the middle is too hot, less air. If the inside is too cold, more camber. And so on.

Different tires and different setups will require different pressures.

Exactly. But tire heat will range based on alignment, track, etc. It's a good idea to do this though and I really should start bringing mine along to events.

[Touge Factory]

I run 245/40/17 RS3's: 29 front / 28 rear cold.

[rx3]

235/40 17 (R888), 30 psi front / 29 psi rear (cold)