I run the 9000 series on my HD. They are 5 way adjustable with the turn of a knob. For driving to work, etc, I leave them on setting 3 but for pulling the boat or my quads, I put them on 4. The adjustability is great if you tow different loads, etc. You can definitely tell the difference between the various settings, 1 is very soft and bouncy- almost like you need new shocks and 5 is stiff as a board! BTW, I started with the 5000 series and they were too stiff IMO.