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      03-01-2013, 07:46 AM   #5
fe1rx
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Drives: 135i, 328i, Cayman S
Join Date: Jan 2008
Location: Canada

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Quote:
Originally Posted by Jazzy View Post
I currently have 225/255 tires on stock wheels. I am about to order a new set of ZII's for autocross, but want to know if a 235 will fit up front with no issues or should I stick to the 225. Has anyone tried the ZII in this size?

Car is completely stock except for sway bar (running in D-stock).
Since you want these tires for autocross it is fair to assume that your main concern is actually performance (in the literal sense, not in the way the word is often used in this forum).

1) I assume your OE wheels are 7.5" x 18" front and 8.5" x 18" rear.
2) 225/40R18 ZII tires are recommended for wheels from 7.5" to 9"
3) 235/40R18 ZII tires are recommended for wheels from 8" to 9.5"
4) the car has a 50:50 weight distribution so "should" have a square tire setup if neutral handling and maximum total cornering grip is your goal (which it should be for autocross)
5) for what it is worth, I have been using 225 Star Specs all around so I can say from experience that they help the balance. Also, they have enough tractive grip that the rear isn't overpowered too easily assuming you don't treat the throttle like a switch (which of course you don't in autocross, if you expect to do well). My suggestion is that you consider a square setup, even if you manage to fit 235s up front.
6) Whatever you do, you will be hobbled unless you replace the rear subframe bushings with the M3 parts. This is the single best handling mod you can do on your car after good tires. The original rear subframe bushings force the car prematurely into understeer by means of "compliance steer" or "passive rear steer". With the OE bushings (and a square tire setup), the handling feels quite neutral to about 80% and then the car feels almost as if the front tires are rolling over. With the M3 bushings the handling maintains the same feeling all the way to the limit and the sense that the front tires are rolling over disappears.
Appreciate 0