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blubb blubb blubb
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Discussion Starter #1
I'm looking forward to trying my first autocross next weekend. I've got a 2001 325xi with the Goodyear RSA tires of the sport package. I've heard that you should put the tire pressure higher than normal for an autocross. So what's a good range to be in? Thanks.
 

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Head-In-Sand Dumbass
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Well with my 330 + Mich Pilots I upped the pressure about 4psi front / 5psi rear over the stock recommendations. I really liked the grip that produced, not a lot of sliding either. To this day I'm still running them high, not too choppy around town. I noticed absolutely 0 sidewall wear.

With your setup you should play around with pressure... go up 4-5psi and add/subtract from that until you find a comfortable spot. You want to try and make sure that your tire's contact patch is being used during the hardest turns, and not the sidewall (since that's the entire reason behind upping the pressure). Ask around at the autox about how to chalk your tires. This will tell you a whole lot about where the contact patch is stopping.
 

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I recommend starting with 40psi all around which gives you quick response and minimal understeer. What you can do from there is to take a chalk and draw lines on your sidewalls, from the rim straight out to the edge of the tread. Make four lines on each tire 90 degrees apart. After your run look at how much chalk has worn off. This indicates how much your tires are rolling over. If the marks still remain on the edge of the tread then decrease tire pressure; if the marks on the sidewall have been worn away then increase pressure.
 

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zeddy
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JonW said:
I'm looking forward to trying my first autocross next weekend. I've got a 2001 325xi with the Goodyear RSA tires of the sport package. I've heard that you should put the tire pressure higher than normal for an autocross. So what's a good range to be in? Thanks.
At my last autox run, at Lime Rock, the skip barber intructors had me pump my stock 323i's tires up to 45 psi all around.

This kept the stock Conti's from rolling over on the bead.

Ed
 

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Re: Re: Autocross Tire Pressure Recommendations

EdCT said:

At my last autox run, at Lime Rock, the skip barber intructors had me pump my stock 323i's tires up to 45 psi all around.
How did 45 psi feel? I'm especially interested in how if felt in the sweepers (G-circles). I've only used as high as 42 psi. I know I can just go try it myself but I've been pretty tied up lately. Thanks for sharing.
 

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blubb blubb blubb
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Discussion Starter #6
Thanks guys. I'm really looking forward to trying the autocross. I've never done anything other than driving on regular roads.
 

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zeddy
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Re: Re: Re: Autocross Tire Pressure Recommendations

Jspeed said:

How did 45 psi feel? I'm especially interested in how if felt in the sweepers (G-circles). I've only used as high as 42 psi. I know I can just go try it myself but I've been pretty tied up lately. Thanks for sharing.
Jspeed,

It felt really good. My stock tires are 205/55/16's.

My only complaint was the slightly mushy feel on turn in. This impression may have been fostered by driving my car immediately after piloting the school's Dodge Vipers around the course.

Still, I can't complain regarding my car's performance; I was able to get it into the first turn at 65mph lap after lap, same as the Vipers!

Ed
 

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Meat Puppet
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on my 330i I've found best times for my (and your) crappy RS-A's 205 50/17's, at 50 PSI front 45PSI rear. I drive pretty agressivly, and have needed to up the pressures as time has gone on, so 2-5 PSI lower might be a better starting point.

Removing the spare, lightens up the rear a little more, and helps the car rotate nicely. Try to go with 1/4 of a tank of gas.

On my 330 the course is nearly all in second gear, no downshifts needed. You loose major time as you attempt to downshift, in your 325, it should be the same.

The higher pressures really help the tire from rolling over, and tend to stiffen up the steering response (as the RS-A's have a fairly soft sidewall).

Expect the drivers side to feather really bad on the outside edge. RS-A's are NOT good tires to be competitiive with, but they are good tires to learn on, and then get some Falken Azenis, S-03's, or Hoosier's for being competitive.

(You'll have a LOT of fun, if these all season radials aren't squeeling you're not going fast enough.)
 

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Addicted To Autocross
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Here's My Input...

First off, its a great idea to try Autocrossing at least once. You're going to really find out what a BMW is capable of.

JT has already provided good advice with the removal of the spare, and the gas. I autocross ALOT. In fact, I just came from a CSCC practice today and was in San Diego for a BMW AutoX. I used to run 38 front and 33 rear. On the advice of a driver who is REALLY fast, I have been starting with 42 PSI in front and 38 PSI in the rear. Higher pressure in front will induce oversteer.

Remember though that adjusting tire pressures is a way to fine tune your suspension. The car has a natural tendency to understeer, but there are ways to dial it out. In the future, if you like this, you might want to look into camber plates so you can get negative camber in front. The same size wheels (width that is) all around is a plus. Also, adjustable shocks to make the front bounce less and of course sway bars. Set the front to the softest setting and the rear to the stiffest. Finally of course, you can get R-Compound tires which make a world of difference.

Now, this works great with my 330Ci. You're 325Xi may behave and react differently with its all wheel drive, but regardless, you should keep in mind that the main thing is to go out and have fun. It takes time to get good at this, so go in with a good attitude and you'll find that there are plenty of other drivers there that are willing to share information and experience with you.

Happy Driving!
 

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blubb blubb blubb
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Discussion Starter #10
Shinobi and JT,

Excellent info! Thanks. I've never done anything like an autocross before. And I have to admit I'm getting really excited to try it out. Saturday. I'll post how it went.
 

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I haven't autoxed, but I did go through tires and brake pads in 10,000 miles, so I must drive pretty hard. :p I've found that 40-45psi up front makes a WORLD of difference in cornering, especially with the contis. I run 40PSI in back, but you might want to run a touch less. I have more weight back there to carry.

My current pressures are 45F/41R. I'm as happy with those as I'll ever be in this car. (I still miss my old E36's steering.) This seems to give excellent roadholding, while allowing the rear to come around a bit.
 
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