1stoptires: The center hole diameter is about 3"-3.5" and the tire & rim combo is $38.99/tire+$21.99/rim+$5.00/mounting=total: $65.38
I figured the rim would cost extra. That makes the combo a little more spendy. Still a lot cheaper than buying the wheels from someone like roleez. Of course the roleez wheels would be a lot closer to being functional with the hub and bearings already done.
