Piggyback Shock

The springs that come with the snowmobile shocks are straight rate, and they are at the stiffer end of what the progressive rate springs are that they spec on the motorcycle shocks. On the relatively light 550 they ride pretty stiff, but are not harsh. On a bigger bike they would be fine. The damping rate of the shocks is quite firm, but again not harsh. they ride great with a passenger. I would think that the supplied springs would be fine if you sort out the valving, especially if you have a larger bike than the 550 that I have them on.

Another pic with the original springs: