If you ride a motorcycle with a single shock and linkage—whether it has slicks, knobbies or anything in between—the first step in optimizing its chassis setup is dialing-in sag. The amount the suspension settles with the rider aboard has a profound effect on suspension action and handling. Each bike varies, and recommendations are often given in the owner’s manual, but generally that figure should represent one-third of the total travel. You can handle the required measurements with an ordinary tape measure, or use one made for the job such as RaceTech’s Sag Master ($9.99 from www.racetech.com
To check the sag at the rear of your bike, extend the suspension completely and measure vertically from the rear axle to a known, repeatable point on the bodywork. Then have a friend make the same measurement with you geared up and seated in a normal position. The difference in those two measurements is the static or “race” sag. Adjust spring preload until you reach the desired figure. To check the front do exactly the same, but instead measure the length of the chrome fork tube left showing. ASV Inventions offers a Solo Sag Scale ($125 from www.asvinventions.com) that you can use to measure rear sag on a dirtbike without a helper.
Race Tech has a more precise technique for setting sag on its website. Click on the FAQ tab for more information.