It shouldn't be that much of a problem, as long as you have the proper offsets. What I have seen many people do for a exe-pleasing staggered setup is to go with 17" up front and 18" in the rear. I believe the combo was 215/40/17 up front and 225/35/18 in the rear. It added a very aggresive look to the car. However, What I would do for the 17" staggered setup is exactly what you are thinking, and I am guessing you plan to do them with the EVO II wheels.

As far as the tires, there really isn't anything much to worry about. The car is rear wheels driver, so the rear size stock (185/65/15) are 24.5 and the 235/40/17 are 24.4, which is less then 1% error. You should be fine. As for the front, as long as the tires aren't too much smaller to confuse the ABS/ASR that the tires are slipping or something. 215/40/17 are close enough that they will not cause a problem.

Good Luck

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Chirag (Charlie) Patel

99 Mercedes-Benx ML 430 V8 w/custom TV, Video, UHF, speaker system
93 190E 2.6 (4-sale) w/ an amp, equalizer, and CD-changer, integrated w. stock stereo for integrated cellular phone speaker system
2001 C-Class - Maybe (if 190E sells )