I have 15x8 draglites with 275/15/60s with a 4.5"backspace and it is fairly tight, but does not rub. I have aluminum drums which moves the rim out 1/8" vs the steel drum
4" is the perfect BS. Draglites are 4.5" or 3.5". 3.5" will require trimming the wheel lip, 4.5" will require a spacer. I was running 4.5 with a 1/4" spacer and aluminum drums and it fit great.
I have 15x8 draglites with 275/15/60s with a 4"backspace and it is fairly tight, but does not rub. I have aluminum drums which moves the rim out 1/8" vs the steel drum