I got my friend Andy to help me make some measurements. Here is the current configuration of the shock spring preload for my Zongshen RX3.
R1, the first measurement, was made with the rear wheel lifted, and the suspension totally extended.
R1 = 23"
R2, the second measurement, was made while I stood on the foot pegs, with full riding gear.
R2 = 21-1/4"
Race Sag = R1 minus R2 = 23" minus 21-1/4" = 1-3/4" = 1.75 inches
Total suspension travel = 5.6 inches
Race Sag should be roughly 33 percent of total suspension travel. (1.75 inches Race Sag) divided by (5.6 inches total travel) = 31 percent
R3, the third measurement, is the bike supporting its own weight.
R3 = 22-3/8"
Free Sag = R1 - R3 = 23" minus 22-3/8" = 5/8" = 16 mm
I obtained these numbers with the spring preload tightened to 6 turns beyond minimum preload. The shock travel is still a little too soft for me, so I need a heavier shock spring. This situation is also corroborated by the size of the Free Sag.
The current settings give me an acceptable ride, but I will certainly be looking for a stiffer shock spring. I am also interested in an aftermarket shock absorber with more travel, or a shock absorber designed for another bike with more travel.
