Whether you race competitively or just ride the dunes or trails, measuring and setting your race sag is one of the most important things you can do to improve your bikes handling. Even a 1/4″ adjustment can make a big difference in how your bike handles. Before you get your shocks rebuilt, a new tire, or replacement parts, first check the race sag. We’ll show you how to check the rear end race sag on today’s Tech Tip Tuesday.
Check and Measure Race Sag
First off, you need to measure the distance from the axle to the chassis or rear fender with the suspension fully extended. In order to measure the unloaded/extended distance, you’ll need to put it on a stand that doesn’t have any of the swingarm rest on it. Using a metric tape measure will make things easier and more precise. It’s crucial to measure from the exact same points for every measurement so it’s a good idea to mark your measuring points with a piece of tape for reference. We’ll call this measurement R1.
Next measure the suspension with the rider on the seat or standing on the pegs. He/she should be in their riding gear (add 10mm to measurement if they are not wearing riding gear). The rider can bounce up and down a couple times to allow for an accurate measurement. At this point you can subtract R2 from R1 (R1 – R2 = Race Sag) to get your race sag measurement. The ideal range is between 90-105mm. If your bike is not within this range, you will need to adjust the rear spring preload until it’s within specs. In order to do this, unscrew the lock ring (see photo) on the spring and either tighten or loosen the spring by turning the adjustment ring until you are in the desired range. measurement. While someone holds the bike with the rider on both pegs, measure the same two points to get the compressed distance on the rear suspension. We’ll call this measurement R2.
Once you’ve adjusted the race sag to the correct settings, measure the bike with the rider off of the bike and with the bike off of the stand (bike supporting it’s own weight). This will be measurement R3. Take this third measurement and subtract it from the first one (R1-R3) to get the “static sag”. This will tell you if your spring is too weak/soft or too stiff/strong for your weight. If the spring rate is correct it should only sag 15-25 mm. If the static sag is less than 15 mm, the spring is too soft for your weight. If the sag is more than 25 mm, then the spring is too stiff for your body weight.
- For better turning ability and smoother ride (with reduced high speed stability), reduce the race sag to the 90 mm range
- For a harsher ride but better straight line and high speed stability increase race sag to the 105 mm range
- To save time while adjusting preload on the spring, don’t tighten the lock nut ring until you have the sag within specs
- Use a screwdriver or chisel to loosen the locknut and to adjust the adjuster nut
- Measure and adjust race sag after a ride. if you’ll be doing mud racing, leave the mud on the bike so weight will match race conditions