15 x 8 Americans

kevin
i have a 68 cuda with ss springs and the 3/4 off set spring kit. i use a 255 x 60 15 inch steel raylle with 4 5/8 back space on a small bolt pattern. it fits the wheel well very nicely and i have about 1 1/4 inch from the sidewall to the leafspring. and your right the rear end sits up alot higher with these springs.
terry