[elwesso]

So I'm considering running a square wheel and tire setup, and I was considering buying another set of OEM wheels from an M coupe or roadster, and mixing/matching and either running (4) fronts or (4) rears... Seems to me that a car as neutrally balanced as the Z4 M you'd want to run a square setup to make it handle as neutral as possible. I'd also like to be able to rotate the tires if possible.

As everyone knows the specs for the front and rear OEM are:

F 18 x 8 ET42
R 18 x 9 ET30

I want to run 245-40-18 all the way around, I already have (2) brand new 245-40-18 ready to go on the car.. You could run a 245-40 on either an 8" or a 9" wheel, with the 8" being preferred IMO.

Doing some quick calcs, it appears that if you were to run the rear wheels on the front, they would extend 25mm (or about an inch) from where the stock front wheels are.

After doing a little research, it appears on the fronts, an 8.5" ET35 fits pretty good in the front, so I've been using that as my baseline.

So, comparing the stock fronts to an 8.5" ET35, those extend an extra 13mm (or about 1/2") from the stock, so the rear OEM wheels on the front would extend about another 1/2" beyond that (12mm).. My guess is that will not work with a 245 tire.

Now, comparing running the front wheels on the rear, they will retract by 25mm, so it appears running the fronts on all 4 corners might be the best bet with 25mm spacers in the rear. I'm not tickled to death about running 1" thick spacers on the rear, although it appears from my research that if you want to run a square wheel and tire setup, running spacers in the rear is unavoidable if you want things to look reasonably close to stock..

The third and final option, which I'm also not fond of, is to run the same size tires on all 4 corners and have them rotated off the car, which again I'm not thrilled about.

My "master plan" on doing this would be to effectively have (2) sets of OEM wheels. I'd buy a set of OEM wheels, put together a set of (4) either fronts or rears, and sell the remaining (4), hopefully close to what I paid for the original set. Or, if I could get lucky maybe I could find single fronts or rears depending what direction I go.

What do you guys think? Am I crazy? Should I just run a staggered setup on the OEM wheels and be done with it?