ORIGINAL: charlos

preload will change the sag settings, but it doesn't change the rate of the spring (unless it's progressive, and it might be, but even then it just changes the progressive characteristics of the spring.). a 16kg/mm spring will compress 1mm for every 16kg of load, regardless of the preload setting. but the preload setting determines the baseline for which the spring will actually start working--as in, if the spring is preloaded 5mm, the spring will not compress until there is 5*16kg or 80 kg on the bike. after there is, it will still compress at its rate. in the end, proper sag is VERY important, but if the spring is the wrong rate (too soft or hard), then sag settings won't correct that condition.