Suspension Sag Calculator

Suspension sag is how much a motorcycle's suspension compresses under load, and measuring it correctly is the standard first step in setting up spring preload. This calculator uses three length measurements taken at the same reference point (typically the axle to a fixed point on the bodywork): Fully Extended Length with the wheel off the ground and suspension fully extended, Unladen Length with the bike on its own weight and no rider, and Rider Length with the rider seated in a normal riding position. Static Sag (sometimes called free sag) is Fully Extended Length minus Unladen Length -- how much the suspension compresses under the bike's own weight alone, which mainly reflects spring preload setting.

Rider Sag is Fully Extended Length minus Rider Length -- how much it compresses with a rider aboard, which is the figure most commonly used to judge whether the spring rate itself is appropriate. The widely used target for Rider Sag is roughly 25-33% of Total Suspension Travel (tighter, around 25-30%, for race setups; slightly more, around 30-33%, for street use), and this calculator's Recommendation output flags whether your measured Rider Sag falls too far outside that band, which typically points toward a spring that's too soft or too stiff for the rider's weight rather than a preload-only adjustment.