Sponsored by The Tire Rack

[roamer]

Gang-

After a great deal of research, measuring and trial fitting, I think I have narrowed down some key measurements that you can use when thinking about larger wheel/tire combos. These will allow you to run a given combo without fender rolling or playing with camber - so it is geared for primarily street driven cars. Also, obviously, this does not take into account your suspension height or the thickness of any aftermarket coilovers (but it does assume a sports suspension ride height). So, the lower you go, the narrower you will need to be (and similarly - the taller the tire, the narrow it needs to be).

With all the usual lawyerly caveats (i.e. don't blame me if it does not work for you or if you are an idiot), for the benefit of others, I thought I would share.

The critical maximum measurements are the following:

(1) Overall tire diameter = 25.5" max

- Also remember you need to keep the front and rear within a max of 1.0-1.25% of each other to avoid causing havoc with the traction control.

(2) Front Back-Spacing = 6.5"

- This is critical, otherwise you will hit the strut housing.

(3) Front Front-Spacing = 3.5"

- Yes boys and girls, you CAN run a 255 up front with the right offset, diameter and ride height.

(4) Rear Back-Spacing = 7.5"

(5) Rear Front-Spacing = 4.1"

Now, to figure out whether that ridiculous offset or tire size will work you need a few calculators. First, the excellent calculator tirerack has provided. I also found this calculator very valuable for playing with offsets and tire widths (http://www.autolounge.net/calculators/tirespacing.html) to turn the offset and tire/rim width into front/back spacing.

One last thing to keep in mind, most tires do not necessarily measure to spec, so make sure the tires do not exceed the calculated measurements to such a degree as to cause problems.

All of this info and calculators is equally valuable for other 3-series cars if you know where the pinch points are.

I hope this helps and good luck.