I have installed Progressive springs in my 2017 Sixty. The rear shocks have progressively wound springs. I think the improved rear shocks came out on the 2017 Scouts. I initially installed Kuryakin rear sets but couldn't ride very far before my knees were hurting being at such extreme bend. I then switched to mini board which allowed me to move my feet around a little bit. The biggest improvement was being able to stand up a bit when I saw large bumps in the road or crossing railroad tracks. Now that I have the 1920 solo saddle I have enough leg room to put the rear sets on again. After 3 yrs. I still couldn't get used to feet forward position. Now I can stand up on the pegs on rough roads and deep gravel. My only complaint is sliding around on the smooth leather of the seat and it could use a little more foam. I will take the seat to a local shop next winter and get it upholstered in a less slippery material and have better foam installed. The bike fits me now the way I like. To me, new fork springs are the biggest improvement.