hyperpro rr shk sprg flde deluxe 2 sp hd17 ssb016bProgressive rear Spring is designed to smoothly Transfer Engine Power to the Road Whilst Controlling Your Bike, Ensuring More Stability and Will Significant Reduce Tire Wear, Shorter Braking Distance, Better Balance in the Bike, More Comfortable Riding, Even with Passenger, Easy Corner, Easy Corner, Easy Corner Confidence, it makes you feel more comfortable and or aunt, overalls Sense of Confidence in the bike