I think you'd want to keep the same size all around since your wheels are all the same width.

If you had gone with a staggered setup, you'd want the rears wider.

 

Since you didn't purchase a staggered setup I would just run all 4 wheels with the same size tires.

 

235/40R18 is a good setup. I went with 225/40R18 for my 18x8.5 wheels

 

One last question gentlemen,
I drive an 04 325Ci, an like i mentioned on my first post I already ordered the VMR csl style wheels 18 X 8.5 all the way around but would this setup look awkward. Would the rear and front sticking out evenly look unusual. Would 9" in the back look more natural? Not sure guys...would do you think? MODBargains chime in on your professional opinion.

Regards,
Joe

 

Hey I used to have 18x8.5" CSLs on my car. It will look great. People get a staggered setup because it looks a bit more aggressive, but you also loose the ability to rotate the tires. The rear fenders just have a bit more room so people try to fill up the space with a wider wheel/tire combo. If you wan you could run spacers for the rear of the car and push the wheel/tire out a bit of you would like. We carry the H&R Trak spacers as well if you're interested.

Here are some pictures of my personal car with 18x8.5 CSLs on it. I'll let you be the judge. I was actually running a 5mm spacer in the FRONT to help clear my KW coilovers. So I had a 35mm offset and a 40mm offset.

 

235/40/18's look great on all 4 corners. They sit nice and square.

-Charles@VMRWheels
www.vmrwheels.com

 

run 235 35 18 it have a lot of meat and look nice 235 40 18 is going to be to much especially if the car is drop

 

235/40/18 is the correct size to run to keep the OE diameter of the wheel.