The 4&5" belts were originally used on Top Fuel Drag Bikes because the belts were lighter and stronger for the massive horsepower of Nitro Fuel. Some claim the belts are smoother in the Primary than a chain. I personally like the look of a closed Ptimary. My Motor puts out 120hp at the rear wheel so I use chains. Plus the belts are really expensive to replace. Also I have friends who have had fingers cut off by belts. Yes the belts look cool but there not for me. Hope this helps. I can find a chain any where, belts are hard to find on the road if you break one and they do break.