Bent frame, bent swingarm, bent shocks, weak shocks, old bushings, worn out bearings, worn out chain, worn out sprokets or bent, bent wheel, worn out tire or defected, out of balance wheel and tire, misalignment, bad brake rotars bent or worn, bad pads, calipers needs rebuilt or change, bad brake lines, dirty resovoirs, change clean and check all items I listed should have no problem or what you will spend you might want to purchase a new bike. Oh check the front end for excessive bottoming out. Or it could be caused by you, if you weigh more then 150lbs, you wanna purchase a bigger bike, your putting stress on all the parts.