A friend with a stock non-m Z4 3.0 came by the shop the other day, so I took advantage and did some test fitting of 17" track setups. I did not take the photos so a number of ideal shots are missing.
17x9" ET42 Square with no spacers. 255/40/17 Nitto NT-01 r-compound tire
This setup fit perfectly up front. Strut tube clearance was fine, as was fender clearance. Any more aggressive and it would have fender issues though, so this is the limit in offset/width for a stock application. Sadly I don't have detailed photos of this front fitment, but I can verify that it was clean, and would only be aided further with camber plates.
Here is a shot of the rear
Rear clearance was easy. I would classify this as a conservative rear fit. There is room for this setup to be pushed further out. A 12mm spacer would make the rear fitment flush with the fender. Flush is not ideal for a track setup as you need the tire to fit under the fender, but if a narrower tire like a 245/40/17 were used, it would be ok to push the wheel out more for aesthetic purposes.
This test showed that it would be easy to run 17x9" ET42 square with 255/40/17's on a stock car. There is no reason to go more conservative for fear of strut tube clearance as I could easily fit a finger between the wheel/tire and strut tube.
17x9" ET30 rear with 255/40/17 Nitto NT-05 extreme summer tire
This setup is the equivalent of running a 17x9" ET42 wheel with a spacer. The new concave 17x9" ET30 wheel is spacer free, concave, and lighter than the previous higher offset 9" wheel.
The wheel is flush with the fender, but the 255 extreme summer tires run narrower than the previously tested r-compounds. The bead protector and part of the sidewall stuck out of the fender, but the actual corner of the tread was still within the fender on this setup. This is aggressive already, and could require a fender roll to eliminate all rubbing. I'd say there is a 75% chance that this setup would have no rubbing without a roll as long as the tire is no wider than what was tested. With either added negative camber or a roll, you could get away with more.
17x9.5" ET35 rear with 255/40/17 Nitto NT-05 extreme summer tire
The offset difference between this wheel and the 17x9" ET30 wheel makes the face of this wider 9.5" wheel only 1mm more aggressive. The rest of the wheel's width is pushed inward. The benefit of this is that the tire is centered further inward vs. on the 9" wheel. This combined with the slight stretch to the tire make this a usable rear fitment. This is the most aggressive of the 3 test fitments, but it still works. A fender roll in the rear would definitely eliminate any possible rubbing if a meatier tire like an r-compound were used.
17x9.5" ET35 with 255/40/17 Nitto NT-05 on Front
This test was only done to measure strut tube clearance. No spacer was needed to clear the strut tube. We do not have a test fit on the ground as this setup would definitely stick out of the fenders on the stock car an unusable amount. Camber plates could allow this front setup to fit with 2.5-3 degrees negative camber.
The 9.5" ET35 wheel will not fit up front on a car without camber plates. It would stick out of the fender at least 10mm.
After performing this test I would consider one of the following setups:
- 17x9" ET42 square with 255's - easy fit
- 17x9" ET42 front with 245's or 255's and 17x9" ET30 or 17x9.5" ET35 rear with 255's for a staggered street setup.
- 17x9.5" ET35 square with 255's - needs camber plates, but would be ultimate 17" track setup.
17x8.5" ET40 - 17.2lbs
17x9.0" ET42 - 17.4lbs
17x9.0" ET30 - 16.55lbs
17x9.5" ET35 - 16.95lbs