Shock Spring Preload
The last post was pretty close, but the measurement he gave is way off - you want about 4 inches of sag when you are on the bike in all your riding gear. Put the bike on a stand with the rear wheel off the ground and measure from the rear axle to the rear fender. Then take the bike off the stand and sit on it with someone holding it. Have someone now measure from the axle to the same spot on the rear fender. If it is more than 4 inches, tighten the preload adjust ring, if it is less, loosen it. 4 inches is usually a good starting point. If you have less, the rear end will sit high which may make the bike turn better, but be less stable at high speed. If you have more than 4 inches, the rear will squat, making turing a little slower, but it will headshake less at speed. Hope this helps!!