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      02-26-2013, 01:42 PM   #1
elwesso
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OEM front/rear on all 4 corners?

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?
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      02-26-2013, 04:27 PM   #2
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limiting yourself to the 224's is tough, and expensive. imo the best option would be to run 4 rears w/ your 245's and get a shim kit to add more neg camber in the front. it should be just fine, but you'll need an alignment for sure.

i think your "master plan" is to be able to rotate in general? if not, then go with somebody like apex where you can get identical rim widths but stagger the offsets front-to-rear; 9.0 et42 front and 9.0 et31 rear. that front size would likely need a small spacer with anything larger than a 255 up front.
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      02-26-2013, 05:01 PM   #3
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I really don't like the idea of adding more camber to make a wheel and tire combo fit.. I figure the engineers at BMW got the alignment settings and suspension geometry correct the first time, so I'd rather not mess with that. I think I'd rather run spacers than mess with that.

I really want to be able to rotate tires from corner to corner, and I'd prefer to keep it as simple as possible. If it turns out to be too complicated, I'll just run 255's in the rear on the OEM wheels and call it a day.
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      02-26-2013, 05:57 PM   #4
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Square setup for what use type? Street? Track?

245 square for track isn't enough rubber IMO. 265 square, sure, but not 245.

Also, fwiw, 245 rear isn't enough rubber either. Stock is 255, and I think that's bare minimum. IMO it would be hard to put down power mid-corner with that tire combo. If you're going to square it up, square it up on the front by going wider there, not by going narrower rear. My 2 cents.

Last edited by Finnegan; 02-26-2013 at 06:10 PM.
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      02-26-2013, 08:20 PM   #5
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Quote:
Originally Posted by elwesso View Post
I really don't like the idea of adding more camber to make a wheel and tire combo fit.. I figure the engineers at BMW got the alignment settings and suspension geometry correct the first time, so I'd rather not mess with that. I think I'd rather run spacers than mess with that.

I really want to be able to rotate tires from corner to corner, and I'd prefer to keep it as simple as possible. If it turns out to be too complicated, I'll just run 255's in the rear on the OEM wheels and call it a day.
The question Fin asks is a good one. IMHO, if this is just for the street you can leave the camber alone.

If you do track the car, the stock camber settings are way too conservative and the car will understeer like a pig. Pushing the camber out to -2.0 to -2.5 with a zero toe will wake the car up handling wise....

Just my two cents.


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      02-27-2013, 08:27 AM   #6
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Thanks guys, really appreciate the thoughts!

I want to have my car track-ready... My plan is to try and do at least (1) track day this summer, and probably a handful of local auto-x.. I really want something setup that I can run on the street and the track. Most of my driving will be on the street, so I don't want something that's crazy and will kill tires.. -2.0 camber with (0) toe doesn't seem outrageous for a street-ish setup.

While I haven't gotten a chance to drive my car very hard yet (only driven 3 times since I bought it in Dec), it seems to me like in stock form the car would understeer quite a bit. Obviously by having significantly more grip in the rear than the front you're going to make understeer worse, and being close to a 50/50 weight balance putting that much more rubber on the rear than the front would seem to be understeer city..

Perhaps the best setup on the OEM wheels might be a 245-40 front and 265-35 rear or 275-35?
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