small bolt pattern steel wheels

I don't know if that is how wheel manufacturers measure backspacing or not. I laid a board across the edge of the wheel (no tire installed) and put the ruler down to the backside of the mounting surface. As most everyone knows a 5.5 wheel will actually measure approximately 6.5 outside to outside as wheel width is determined at where the bead hits the wheel (approximately 1/2" inboard on each side). Hope it helps.