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      01-07-2013, 08:46 PM   #11
cgroppi
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Drives: 2007 Z4 M Coupe
Join Date: Mar 2010
Location: Tempe, AZ

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I run my Z4m in AS. I am certainly not a national champion level driver, but the car can be reasonably prepared.

I run Koni DAs from TC Kline, and looked into getting AST 4200s. I eventually did not, but they will happily build you a set for stock springs as long as you're willing to wait for a few months to get them. You need to send them a pair of donor struts so they can cut off the spring perches.

I have run two tire setups: 285-30R18 Hoosier A6 all around, and 245/275 Goodyear Eagle RS. The Hoosiers mount just fine on the stock wheels, and there are no clearance issues at all. In the rear, a 5mm spacer is required to clear the fender liner.

With the Hoosiers, I ran a UUC front bar. With the staggered Goodyears, I use a Ground Control "race" rear bar to bring more weight transfer to the rear to help get rid of understeer. I think I like the second setup the best, but they're not too hugely different. I think turn in was better with the big fronts, but I can get the overall balance much more loose with the rear bar and the staggered tires. I had to have the compression maxed in back and full soft in the front with the hoosiers, and I still got understeer. With the rear bar, I have the rears full soft and the fronts about in the middle of the range. I have no issues with the big rear bar limiting traction. The M LSD is really good.

Now that Goodyear has bailed from autocross, I am pondering what to do next: Go back to the square 285 A6 setup, try a staggered A6 setup (maybe 255/285) or try Kumho 710s (245/285). The Kumhos are obviously worse in the grip department, but they do last a long time. It's a battle of cheap vs. fast .
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