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What is suspension sag and how can I measure it?

Friday, October 19, 2018

What is suspension sag?

Suspension sag, or loaded sag, is the amount of suspension travel used when a rider sits on board a bike – as the bike ‘sags’ under the rider’s weight. It’s important to ensure your bike has the correct amount of suspension sag – too much and you’ll end up bottoming out your suspension too often, and too little will make the suspension feel stiff, with not enough give on potholes or speed bumps.

Motorbike Suspension Sag

How to measure it  

When it comes to measuring suspension sag, we’d consider the race tech method to be the easiest and most accurate. It involves taking three measurements and using the following equation to work out how many mm your optimum loaded sag should be: L1-(L3+L2)/2.

The ideal range is for your suspension to compress by roughly 25-30% of your wheel travel – although this depends on where you’re riding. To measure your suspension sag, grab a couple of friends and a tape measure and you’re good to go.

Step 1: Before getting onto the bike, fully extend the front suspension and take a measurement from the fork seal to the bottom triple clamp - this is measurement L1.

Step 2: Sit on your bike in your regular riding position, wearing your normal kit including your helmet. Have one friend hold the bike steady, whilst the other takes the same measurement after pushing down on the front suspension, and then letting it settle. This measurement is L2.

Step 3: Finally, take the same measurement again but this time after lifting the front and letting it settle - this measurement is L3. Ideally you want L2 & L3 to be the same.

Step 4: Now you can do the same for the rear suspension. As with step 1, extend the suspension (without anyone sat on the bike) and measure from the axle to a solid point directly above. Then do steps 2 & 3 again but for the rear suspension.

Typically, for street riding, you can expect the correct movement range to be 30-40mm for both the front and rear suspension. You can then make incremental adjustments depending on whether you have too much sag, in which case you should tighten up the front preload – or too little, which requires you to loosen the adjustors.

Our next article will focus on the different types of suspension sag, as well as how sag should be adjusted depending on the specific need. If you’d like help adjusting your suspension to ensure it’s set up correctly – get in contact with us and we can arrange a time for you to drop by.


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