I have always enjoyed the look of the M6 wheels, but when I saw a set on an 850 on the forums, I just knew I had to own a set for my car. After browsing classifieds for a few months a mint set of original wheels emerged (it was also a pretty amazing deal that I couldn't pass up so I was quick on my feet to pick them up). They have been sitting in my basement ever since I got them, so I figured I'd make a post about some math as to what is needed to make a set fit your E31 (or maybe just a lesson in offsets).

First thing is first, these wheels will not clear your front suspension components on a E31 without spacers (the rears are not bad, but will clear without any spacers). Wheel fitment either makes the car, or ruins it - this is one of those things that needs to be done correctly and will look like this when it is all done (this is just a photoshop rendering, but you get the idea):

The good thing about these wheels is that they have a center bore diameter of 72.6mm, which is the same size as the E31 (thus not needing any hub-centric rings to rectify vibrations during driving). The factory wheels on an E31 have much lower offsets (especially the fronts) then that, which means for a proper fitment wheel spacers will be needed.

E63/E64 M6 wheels specs:

Front: 19x8.5 ET35mm
Rear: 19x9.5 ET20mm

E31 Stock staggered specs:

Front: 17x8 ET10mm
Rear: 17x9 ET19mm

The difference between the front factory wheels and the M6 wheels is pretty drastic, but it's definitely fixable with a set of spacers. I didn't bother taking any pictures of the front wheel fitment without spacers since they just hit the shock insert tube. To get the front wheels to clear the front suspension you need to get them closer to ET10mm. To do this you need to compensate:

Front: 35mm (offset) - 20mm (a spacer) = 15mm (end result for new offset)

This would put us very close to original specifications (even a little further since the M6 wheel is .5 wider), however if you are a fender hugger and love your rims ultra flush... you may want to go with a 25mm spacer for the front. Getting spacers for the rear wheels is arguable if you wish to do it or not, since they are almost the correct offset (and wider so they will fill the wheel well even better then the factory wheels). 5mm spacers don't have the hub-centric rings which might cause a problem. Using a set of 8mm ones may be a better idea. Here is what I plan on going with though:

Rear: 20mm (offset) - 5mm (a spacer) = 15mm (end result for new offset)

As for the wheel spacers... the best place I found for a set of H&R ones was Modbargains, which is where I plan on getting my set. That or ECS Tuning, they have some nice spacers too.

Here is a picture of how these wheels fit on the rear without any spacers (I know my car is dirty - its winter!):

What tires will clear your suspension and wheel wells? My car is lowered so I have to be a bit more conservative with my tire selection (especially the front).

Tire sizes:

I went with the underlined sizes.

Front: 235/35/19, 245/35/19, 255/30/19
Rear: 265/30/19, 275/30/19, 285/30/19

That's about it though for fitting these wheels. Hope it was helpful.