SAG
Measure MTB sag in percent and millimetres
Sag is how far the suspension settles under the rider. Use the correct travel or stroke.Fork sag
Use fork travel. A 160 mm fork at 20 percent sag settles 32 mm.
Rear shock sag
Use shock stroke, not rear-wheel travel or fork travel. A 55 mm shock at 30 percent sag settles 16.5 mm.
Repeat the method
Wear full riding kit, release any lockout and measure on level ground.