Bought a 96 Dolphin 535 last fall. Drove it from Flint, Michigan home to Terre Haute, IN ( about 550 miles). Very sloppy steering and a vibration that started at 40, peaked at 48, and stopped compl...
Mike....Feeling it in the seat of the pants is typically an indication of the rear tires bouncing around or a drive shaft issue.
Did you balance the rear tires when you put them on? Do you know if the Double Coins were ever balanced on the tag? Since the tag doesn't carry as much weight as the duals, an out of balance tire on the tag can tend to bounce around a little more.