The backspace is the distance from, uhh, lesse here. If you lay the rim on the ground, with no tire on it, face down, and measure the distance from the highest part of the wheel, which is the inside edge when it is mounted, to where the wheel bolts to the hub, then you have the backspace. Wow, that should screw you up fer a while. As fer tire size, whydontcha just run whatever the IMSTOCKS had? Should be cheaper than other tires in that range. REmember, there are front and rear wheels in the 16" F-car wheels.