89 because its what is sugested and my bike has a knock sensore, on the harley i run 87, because no matter what i put in it, it will burn and stick shake and rattle HAHA. The lower octane does give more power, IF the engine does not spark knock or detonate. Higher octane fuels are just slower burning and also less likly to preignite. Someone else chime in if im barking up the wrong tree.