I have a trailer that I don't know the age of,the tires are 480x12.what would be a good replacement shock? i can feel it bouncing around, my boat is maybe 900# with the trailer and all. Not sure if a softer shock would be called for or a combo of a softer tire and shock?I know that the trailer tires have a stiffer side wall.just don't care for bouncing and vibration.any suggestions ?