I want to go with the extra heavy duty rear springs for my XP 163. The way I understand it skidoo makes springs that are one level stiffer than stock, and also springs that are two levels stiffer-usually made for 2-up riders. What are the part numbers for the stiffest springs? Before I get instructed on the search option, I already did that but found people posted different part numbers for what they called the extra stiff springs. Thanks
