What MM back spacing???

what MM back spacing do i need for 18x9.5??? i searched for it but couldn't find it...thanks

Usually backspacing is measured in inches, maybe that's why you're not finding it. A 9.5" wheel on a 4th gen needs about 7" of backspace, that would be 178mm.

Dave

well the wheels i want (C6R's) 18x9.5 + 56mm so i was assuming that was the back-spacing...guess i'll just call em when i'm ready to buy

In the wheel you mentioned, 56mm is the "offset"... the distance the mounting face is moved out ward from the centerline of the wheel. That is the correct offset for a 9.5" wide wheel on a 4th Gen. Anything from about 45mm to 56mm will work. The 56mm offset will give you a backspace of about 7.4 - 7.5".

In the wheel you mentioned, 56mm is the "offset"... the distance the mounting face is moved ******d from the centerline of the wheel. That is the correct offset for a 9.5" wide wheel on a 4th Gen. Anything from about 45mm to 56mm will work. The 56mm offset will give you a backspace of about 7.4 - 7.5".
ohhhhhhh...that makes more sense...thanks!!!