Sag

Sag is the amount the suspension compresses from fully extended under load. Static sag (free sag) is measured with only the bike's weight, and race sag (rider sag) with the rider in riding position and full gear. Sag keeps the wheels able to extend into dips as well as compress over bumps.

It is adjusted with spring preload. Typical rider sag is roughly a quarter to a third of total travel; for example, many motocross bikes use about 100–110 mm at the rear. Always use the manufacturer's or your suspension tuner's recommended figure.

Measure with a helper and a tape: fully extended, bike on its wheels, and rider on board. If you cannot reach the right rider sag and static sag together, the spring rate is wrong for your weight.