Currently car has stock 17's, the 17x7 +45 I believe. I am moving to 18x8.5 +35 up front and 18x9.5 +40 in the rear. Anyone know optimal tire sizes so I do not throw off the VDC? I am dropped 1.5" all around also. I was thinking 225/45 up front and 255/40 in the rear. Anyone with experience have other suggestions?

 

After doing some research and calculations you can do two different setups with wheels this size. You can do 225/45/18 front and 255/40/18 rear and get a slight stretch. This will leave you about -1% off all around. Or, if you want EXACT equal fitment then you should do 235/45/18 front and 265/40/18 rear. This will give you less than 0.5% difference all around, the most accurate. Just wanted to update in case any other X guys are interested.