AutoX and Tire Pressure

[paco_swava]

So i was messing with tire pressure last weekend at the autox here. I was always under the impression that you lower the pressure to get more traction and even talked to a couple guys that ran that way. Long story short... i'm starting to think otherwise. When i got to the track, my tires were at about 31-32psi all around. After my first 4 runs, i decided to fill up to about 35. My last 4 runs gained me around 1-2 seconds. Granted, there was alot of rubber laid down from the r-comp tires that ran before me, but still. That's a big jump.

I guess i'm just curious as to what pressure other guys are running, and what is working for everyone else. Any input would be awesome.

Here's what i'm running:
CAI (ebay)
Powder UDP
PaceSetter CatBack
21mm rear sway
Lowered about 2 inches
Falken Azenis 205/50/15
Pots Mod

[STS-ZX2SR]

40F/30R +/-2. 215/40-17 Z1's on 7.5" wheels on 550/375 springs.

[Manbearpig]

Raise the pressure = more grip

Lower the pressure = less grip

There is a point where it can easily be raised to much and hurt performance. It's different for ever suspension setup and tire so usually start with 4 or 5 psi up and raise or lower depending how it feels each run.

Just for reference, I take mine up about 4 psi in the front and 5 in the rear.

[STS-ZX2SR]

Raise the pressure = more grip

Lower the pressure = less grip



That's not entirely accurate. You raise pressures to keep the tires from rooling over onto the sidewalls. Tires are like a spring. If you raise the pressure you'll be stiffening the spring rate on that end...less pressure is like a lighter spring. You generally want to set the pressure to maximize the use of the whole tread in front--including having somewhat consistant temps across the face if you care to measure those. Generally (on FWD) the rears are set to tune the handling with respect to rotation.

[ZXTool]

I run 40psi all around and that seems to be the best for my and my mods.

[godspeed]

I set the front at 42 and rear at 40 before I leave home for an event. After a few runs at the last event, my fronts had heated up to 48 and the rears to 45.
I prefer to start out too high, as it's easy let air out. I don't have a portable compressor, so I'd be kickin myself if I went to an event with pressures set too low.

[Entropyman]

So i was messing with tire pressure last weekend at the autox here. I was always under the impression that you lower the pressure to get more traction and even talked to a couple guys that ran that way. Long story short... i'm starting to think otherwise. When i got to the track, my tires were at about 31-32psi all around. After my first 4 runs, i decided to fill up to about 35. My last 4 runs gained me around 1-2 seconds. Granted, there was alot of rubber laid down from the r-comp tires that ran before me, but still. That's a big jump.

I guess i'm just curious as to what pressure other guys are running, and what is working for everyone else. Any input would be awesome.

Here's what i'm running:
CAI (ebay)
Powder UDP
PaceSetter CatBack
21mm rear sway
Lowered about 2 inches
Falken Azenis 205/50/15
Pots Mod

I run the same tires and I run 36psi front and 32psi rear. The car seems decently balanced at those pressures. I run the S/R springs and struts and a Progress rear bar on the soft setting.

[ZXTool]

I run 40psi all around and that seems to be the best for my and my mods.

Forgot to mention i'm running on 205/45/16s also.

[zxtwou2]

i have 215/40R17 Nitto Neo-Gens up front....215/40R17 Yokahama Avid H4's on back. i know..i need much softer tires..i'm workin on it.

when i run well..i'm at 40 up front, 35 in the rear.

[paco_swava]

Sweet, thanks for all the suggestions. Sounds like i'm def starting too low. Of course, i'm still waiting for my coilovers, so that will change alot as well.

[iceracer]

Rear tire pressures can go both ways. Many stock class cars run much higher in the rear.
As STSzx2 said, and I have said, tires have a certain spring rate. It is a matter of what works best, higher or lower and how the driver feels about the handling.
A lot will depend on your suspension set up.

[iceracer]

The reason a softer tire pressure loses traction is that as the tire rolls over some of the tread is lifted off the road. Less tread contact= less traction.
Higher rear pressures vs lower pressures in the rear achieve pretty much the same thing.
It is just how you want the car to handle. Higher makes the car nervous, reaction is quicker than lower. Some cars/drivers like a lot of difference others don't. You have to experiment.

[iceracer]

A little aside on the low pressure myth.
When my ice racing club started the unstudded class, many drivers dropped their pressures thinking more traction. Then it was found that higher worked better even on ice. Not as high as auto cross. I ended up running 35 Psi all around. The front tires will actually build pressure as much as 3 psi in a 20 min. race.
PS: I was not one of the lower pressure guys.