I put stiffer springs in the sled last night. 503-189-992 and 503-189-994. they are 11.1 and 73*. On the softest setting they act like the stock spring on the stiffest setting. I recommend these for anyone that is over 200#. I am 210 and on the softest setting the coupler blocks sit where they are supposed to, right in the middle. I haven't had a chance to try it out on the bumps yet but I can tell that it will NOT act like a bucking bronco on the trails. Another thing. If I were to put these on the stiffest setting, I bet I could jump the sled off the roof without it bottoming..