RallyCross Tire Pressure Recommendations

AndersGreen · **Posted:** Mon Feb 02, 2004 11:28 am

We had quite a few folks this weekend de-bead. So, while the rule of thumb in autocross is often "start at as low a pressure as you can go without scrubbing your sidewalls", in rallycross you could say "as low as possible before you de-bead your tires".

I was running 45 psi and didn't have any trouble with my flimsy stock tires. If I had rally tires I would have run at about 32. But those sidewalls are 3/4" thick. I know that some people running 35 psi de-beaded.

So, if you de-beaded, or didn't, post you tire pressures.

Cheers,
Anders

MikeWhitney · **Joined:** Wed Aug 20, 2003 9:15 pm **Posts:** 4724

We did fine most of the day at 35. Then when we saw other people losings tires, we bumpd up to 40. Then we lost one. Coincidence? Probably.

I think it was from smacking into the biggest of the ruts on the far side of the course with some steering dialed in. BAM! Sounded like the front end of that poor car was going to fold in half.

Stephen Westerfield · **Posted:** Mon Feb 02, 2004 11:37 am

Reporting for the Pontiac Rally Am Rental...

We didn't check the pressure before we started...probably a mistake.

After we de-beaded the first tire, we inflated our front tires to about 46psi...5 runs later (the same driver as the first time) de-beaded the tire again. When I fixed that one...we noticed that the other front tire was down to about 18psi...so looks like we were close to losing two of them, that would have been a mess.

They were Goodyear Eagle GA's (Got Airs?)

SimonWright · **Posted:** Mon Feb 02, 2004 11:44 am

MikeWhitney wrote:

We did fine most of the day at 35. Then when we saw other people losings tires, we bumpd up to 40. Then we lost one. Coincidence? Probably.

I think it was from smacking into the biggest of the ruts on the far side of the course with some steering dialed in. BAM! Sounded like the front end of that poor car was going to fold in half.

I hit that same hole during a fun run and popped the bead on front-right. Also dislocated the bumper at that point. Fortunately Kevin Hoff managed to reconnect it for me. I think I have some scraped paint though.

I was running with 39 at all for corners - next time I think I'll run higher. At least at Four Oaks which seems to rut quite deeply in places.

Lots of fun though.

Did you hear that Miranda's STi got crunched at the car wash?

Simon

Kevin Hoff · **Posted:** Mon Feb 02, 2004 12:06 pm

I was running 40 PSI all around on Bridgestone RE-750's. No bead problems here. It appears that softer streety/M+S tires really need a lot of pressure to keep from getting the bead broken.

--Kevin H.

Thanks everyone for a great event! It was every bit as much fun as the first one, even though I had some mysterious oil smoke problems.

AndersGreen · **Posted:** Mon Feb 02, 2004 12:09 pm

Kevin Hoff wrote:

Thanks everyone for a great event! It was every bit as much fun as the first one, even though I had some mysterious oil smoke problems.

Yeah.... "mysterious". Didn't you say you were at least 1/2 a quart overfull when you checked at the end of the day??? :twisted:

Anders

Kevin Allen · **Joined:** Thu Aug 28, 2003 6:42 pm **Posts:** 3479

ContiExtremeContacts, 40psi front, 36psi rear (same as on the street)

No problems, but we were staying out of the bigger ruts as much as possible.

The key here is to keep the steering wheel as straight as you can throughout the course, steering mostly with the throttle and brake (or keep it floored & e-brake if you're fwd, I guess), and stay out of the ruts. Ruts slow you down anyway when they get that deep.

Of course, if you have really crappy rental car tires, I'm not sure if they can be saved...

:roll:

Vincent Keene · **Posted:** Mon Feb 02, 2004 12:23 pm

Stephen Westerfield wrote:

Reporting for the Pontiac Rally Am Rental...

we inflated our front tires to about 46psi...5 runs later (the same driver as the first time) de-beaded the tire again.

Yeah I would have thought that 45psi+ would have been plenty, but as it turned out that wasn't the case. We were driving pretty hard (as were most of us) but those deep ruts are what did us in.

I'm not sure how high one would need to go pressure-wise to prevent "de-beading" in the future. Anders, do you know of any other method to prevent it? Like using silicone around the rim, or even duct tape? Any crazy idea that would keep the dirt from wedging in between the bead and rim?

BTW, this was so much fun I'm looking into getting a beater myself this week. I plan to keep all the body panels attached though. :roll:

Vincent Keene · **Posted:** Mon Feb 02, 2004 12:53 pm

Kevin Allen wrote:

we were staying out of the bigger ruts

stay out of the ruts. Ruts slow you down anyway when they get that deep.

Of course all you 4WD guys got to go 1st...before the ruts got really deep. So I guess you could say you caused 'em! :brow:

I think we need to let the 2WD guys go first next time and see how it goes. :wink:

Kevin Hoff · **Posted:** Mon Feb 02, 2004 1:12 pm

Well it was actually about 1/4 quart...

Mysterious in that I couldn't tell where the leakage was coming from. I'm just hoping that it was the PCV valve, not the turbo shaft seal.

Oh, let's do let the 2wd cars run first next time. The ruts don't hurt us 4wd people nearly as much and I'm sure the 2wd people would like to do something other than an exercise in rut avoidance...

--Kevin H.

AndersGreen wrote:

Kevin Hoff wrote:

Thanks everyone for a great event! It was every bit as much fun as the first one, even though I had some mysterious oil smoke problems.

Yeah.... "mysterious". Didn't you say you were at least 1/2 a quart overfull when you checked at the end of the day??? :twisted:

Anders

Kevin Allen · **Joined:** Thu Aug 28, 2003 6:42 pm **Posts:** 3479

I think we should just make Tom Hoppe & Peter Baio go last next time.

:lol:

The biggest mistake was not re-routing around the loop at the back of the field. I'll know better next time. I remembered it not being too bad when I was driving it, so I didn't even go look at it during the course change to see what kind of condition it was in. :oops:

And the 2nd left turn in the pm was a little tight, too. Have to avoid that in the future.

Carl Fisher · **Posted:** Mon Feb 02, 2004 2:34 pm

We were running our regular Dunlop Sport A2s at 35psi all around and had no problems. And I was not avoiding the ruts- rather I was diving into them and trying to "slot car" around the corners with extra speed.

As for running the 2WD cars first, the decision to do it the other way was not arbitrary. For venues where the course conditions will degrade significantly during the running of the heat, my thoughts are thus:

2WD cars, especially SU2 cars, would be most affected by the course conditions
The course conditions would change most rapidly at first, then less rapidly over time
Therefore the conditions would change the least between the start and finish of the SU2 field if they did not run first.

Make sense?

As an SU2 driver myself, believe me, I would love to have the nicer course to run on. But I still think that doing it the way we have so far is fairer for everyone.

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