Dirt Bike Sag Calculator

How To Take The Three Measurements

1. Fully extended. Put the bike on a stand so the rear wheel hangs. Measure from the center of the rear axle straight up to a fixed mark on the rear fender. KTM calls this dimension A.
2. Static. Take the bike off the stand, hold it upright with no rider and measure to the same mark again.
3. Race. Sit on the bike in full riding gear with your feet on the pegs, bounce a few times to settle it, and have a helper measure again. KTM calls this dimension C. Race sag is A minus C.
4. Optional second reading. Race Tech's method takes one loaded reading after pushing the rear down and another after lifting it, then averages them to cancel out friction. Enter the second reading in box 3b and the calculator averages them.

Use the same stand, the same mark and the same gear every time. Factory Connection notes that measuring from a point off the swingarm arc can throw the number off by as much as 15 mm.

Sag Targets From Owner's Manuals

These are the rear sag figures printed in current owner's manuals. The calculator's presets use the same numbers.

Honda's 2004 CRF450R handbook adds context the others do not: 90 mm of race sag helps the bike turn on tight tracks, while 110 mm adds stability on fast tracks. Yamaha and current Honda owner's manuals that we could access do not print a sag figure, so check with your dealer or a suspension shop for those bikes.

Reading The Result

Race sag first. If race sag is more than the target, the rear sits too low: add shock spring preload. If it is less, the rear sits too high: reduce preload. Measure again after every change.

Then static sag. Static sag tells you whether the spring suits your weight. Honda's handbook explains it: with race sag set, too much static sag means the spring is too stiff for you, and very little static sag means the spring is too soft because it needed so much preload. If static sag is far from the manual's figure, talk to a suspension shop about a different spring rather than cranking preload.

The calculator flags results within 3 mm (0.12 in) of the target as close. That tolerance is our convenience setting, not a manufacturer spec.

What To Do Next

For the full process, including spring rate by rider weight, air fork pressure and clicker basics, read how to set dirt bike suspension. If you are setting up a bike from scratch, our dirt bike setup guide covers controls, tire pressure and gearing too.

MotoMind includes a suspension sag check in its default task list every 25 hours, which you can change, and keeps fork and shock service intervals on an hour schedule for each bike.