The default spring is for riders weighing 140-190 lbs. If you weigh less than 140 or more than 190, I strongly recommend that you replace the default spring with the proper heavier or lighter one. It will ensure optimal performance of your NCX seatpost. This is my 2nd NCX suspension seat post (2nd bike), I wouldn't ride without one, and both have the needed proper spring to ensure optimal performance. It is easy to cheap out and make do with the default, but you suffer less than optimal performance and, for heavier riders, you risk harsh, repeated "bottoming out" of insufficiently sprung suspension. For lighter riders, I'd imagine that you don't get nearly the desired benefit (unless you get the lighter spring) of suspension. I also recommend getting the dust cover, especially if you're riding in dusty areas and/or carrying the bike on a rear rack in dusty, wet, grimy road conditions.