I just went to their website and it looks like that rim is in fact zero offset. An 8.5 inch rim is 9.5 inches wide due to the 1/2 inch lip at the front and rear. Centerline of 9.5 = 4.75 backspace and 4.75 frontspace.
If you know the width and offset of your stock rims you can calculate exactly how much different these will fit.
Edit, I"m guessing the stock rim is 7.5 inches wide and -12? So that is 8.5 inches/2 or 4.25 inch centerline. The -12 offset gives your stock rims 4.75 backspace and 3.75 front space. Those MB wheels will fill the inside just like your stockers, but will poke out 1 full inch.
Last edited by Micahdogg; 05-08-2014 at 11:33 AM.