We test fit multiple combinations of the EC-7 wheel on the Z4 M last Friday. This model is very similar to the E46 M3 in terms of clearance, but with a little less fender side clearance in our experience.
Our first test was our preferred track setup: 18x9.5" with 265/35/18 tires front and rear. This is normally done with an 18x9.5" ET35 wheel front and rear, plus a 12mm spacer in the rear. Because we were using prototypes and only had one of each, we mounted an 18x9.5" ET35 front wheel and an 18x9.5" ET22 rear wheel. This is a spacer free direct fitment that gives the car a great staggered look while remaining square. You do sacrifice the ability to rotate tires front to rear with this staggered offset combination.
The rear fitment is a direct bolt on, but the front fitment requires camber plates, and a suspension that can properly clear the wheel and tire. It is important that the lower spring perch remain above the tire. If the spring or perch is next to the tire, then a thick spacer may be required for clearance which makes the fitment far too aggressive. A 5mm spacer would be acceptable, but anything thicker would push the setup too far out. The stock strut's integrated lower spring perch can clear the 265 setup, so a simple lowering spring and camber plate install can make for a very ideal track setup on the Z4 M. Many coilovers use long springs, helper/tender springs, or cone shaped springs. These may have to be replaced with a single shorter spring usually 6-5" in length to guarantee that the perch remains above the tire.
We had Satin Black prototypes in 18x9.5" ET43 and 18x10.5" ET27 available so we mounted those on the Z4 M as well. To correct for offset, we used a 12mm front spacer making the front effectively ET31. A 265/35/18 front and 285/35/18 rear tire were used for the test fitment. With the amount of negative camber the car had, this front fitment was not an issue. The rear 285 did stick out of the fender and is not a recommended size. This car arrived with a set of 19x10.5" ET22 Volk wheels and 275 tires and there were no signs of serious rubbing issues on the 19" setup, so the 18x10.5" ET27 wheel could be used with a 275/35/18, but attention to inside liner rubbing would be needed as the 10.5" wheel sets the barrel relatively close to an area known to rub on the inside. Generally 18x10" ET25 with a 275 tire is the widest we recommend for the Z4 M fitment.
Another Z4 M came that did not have camber plates installed. The cars only suspension mods were Eibach lowering springs and koni yellows. For this car we used the 18x8.5" ET35 Front and 18x9.5" ET22 rear with 235/40/18 and 265/35/18 tires. The front is an easy fit. A 245/40/18 could also be used on this wheel width. In the rear a 265/40/18 or 275/35/18 would also be a good choice.
The last test was with Anthracite finish wheels. The front was again 18x8.5". The test wheel was ET45 and we used a 10mm spacer to push it out to the ideal 35mm offset. The rear was 18x10" ET25 with a 275/35/18 mounted. The 275 was a Michelin PS2 and not an extreme summer tire like most of our tires. This tire was narrower and had more clearance than an extreme summer tire would.
