Ok, BMW OEM wheels are 20x10 ET 40 front and 20x11 ET 37 rear, Vossens are 20x9 ET 20 and 20x10.5 ET 27.


You can make this work using 20mm spacers for the front and 10mm spacers for the rear, also you have to change hub diameter from X5's 74.1mm to Vossen 73.1mm, so for about $190 you can order such spacers from one of those places:

http://www.motorsport-tech.com/4DCGI/wheel_spacers

You have that backwards. Lower number ETs mean the wheel is further out from the hub-face. Spacers would only exacerbate the problem.

Some people who run spacers on the OEM 20x11 ET 37 wheels, however, run 20+mm spacers. This would mean that the 20x10.5 ET 27 would actually fit without an issue, but you'd want extended flares for it not to look strange.

The fronts would be pushing it even with the extended flares. I'd think it's very possible to have them fit, though.

You're correct in that the higher number refers to the mounting pad being further from the hub-face, but what this means is that the meat of the wheel and tire is sunken more into the car, or closer to centerline. Thus, a very high (positive) offset would require spacers to kick the wheel out more. A very low offset - low positive or even negative - would tend to have the meat of the tire and wheel sticking out of fender.

This picture is a little better at explaining it. You just have to realize what the implication is of the changed mounting point.

http://www.stl-vettes.com/65Vette/Wheel-Tire/wheel-offset-5c.jpg

My bad, you are right.

It can be confusing. I went through a few sets of wheels on my previous car, so it's ingrained in me now. :)

what offset would I need to run a 22x10.5 in the front and rear on my e70 X5??

They offer them in +30 and +38 offsets. I know the rear will be fine regardless but the front I can't make up my mind which would be better?

P.S. I have the fender flares.

Use Rims N Tires - Custom rims, wheel tire packages for your ride - RIMSnTIRES.com to make comparisons.

Great tool!

If you want to run a square setup:
+38 in the front.
+30 in the back

OEM 20" are +40 in the front, and +37 in the back (but 20x11).

+30 in the front may stick out, since the front flares are tiny.
Rear flares are wider, and a lot of members safely put spacers in the back, so a +30 should fit very nicely.