Wheel size does not matter...... You can be running 17's or 18's and still be fine.
It's the TIRE SIZE that will affect your speedo reading. For my 16 x 8" Compomotive CXN's, I'm running 245/45/16's. I still have the correct speedo reading as my stock 225/60/14's on my 14" P-Type wheels.
Ask Don Lew (DonL) or James Razor (Supra GTR) on the recommended size for 17"s & 18"s that will still leave you w/ a accurate speedo reading.