To get the most out of your dirt bike’s handling and suspension you need to set the rear suspension sag. On this episode of MC Garage we show you how.

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Do you weigh the same as the factory motorcycle test riders who were responsible for deciding the final spring rates for your dirt bike? I know I don’t, and because of that my motorcycle will handle differently and perhaps not as intended or designed. Today on MC Garage I’m going to show you how to set your dirt bike sag.

Manufacturers set up suspension for an average weight rider, in most cases that can be anywhere from 160 to 180 pounds—even lighter for smaller-displacement machines. In order to get the most out of your suspension and handling of your dirt bike, you need to set the bike up for your weight. The first step is setting the sag.

What Is Suspension Sag?
Sag is how much the bike settles on the rear suspension from full extension. There are two measurements of sag. Race sag, this with the rider on the bike, and static sag, where the bike sits under its own weight. Contributing Editor Ari Henning did an excellent video on setting streetbike sag, in How To Check Suspension Sag. It’s similar to how we will set dirt bike sag.

Too much rider sag will have the bike sitting too far into the suspension stroke and make the bike feel lazy with less steering response. Effectively the steering rake has increased as the rear has squatted while rotating around the front axle. If the sag is too little, the exact opposite happens. Steering can be too quick or nervous as the motorcycle is up on its nose and the steering angle is steeper.

How Do I Measure Sag?
How do you set the sag? It’s pretty simple and requires just a bit of math, just a few tools, and some assistance from friends. You’ll need a tape measure or a sag scale, which saves you from doing the math. I’ll use a tape measure here so you can understand the math involved. If you have a Japanese dirt bike, a hammer and punch will also be needed for the spring adjustment. For European bikes you need the correct size Allen to loosen the adjuster clamp and that hammer and punch to move the spring adjuster.

Start with the bike on a stand and measure from a spot on the rear axle to the rear fender. Use these same spots throughout this process to ensure consistent measurement. I like to make a mark with a sharpie. Measure it in millimeters and then write it down.

Now with the bike on flat ground, sit on it and have someone hold the bike for you so you can have your feet on the pegs and hands on the bars. Position yourself in a neutral spot on the seat, not too far forward or back. An extreme in either direction will affect the measurement and ultimately the handling. Also, you need to wear all of your gear, including your helmet, chest protector, backpack, or whatever—every pound of weight makes a difference. Give the bike a couple of bounces to find the settling point with you on the bike. Then have someone measure the distance between the two points.

Subtract the measurement of you on the bike from that first measurement of bike sitting on the stand. This is your race sag. You want it to be around 100mm, but check your manual for exact measurements. You can also slightly alter that sag to fine-tune how you want the bike to handle. More sag for better stability off road, less for quicker handling on the track. Just 5mm can make a noticeable difference.

How Do I Adjust The Suspension Sag?
If you have too much sag (over 100mm), you will need to add more spring tension or preload. Too little (less than 100mm) will require less preload. Loosen the spring preload locker; this is either a jam nut on the Japanese models or a clamp on the European bikes. Then tighten or loosen the preload adjuster accordingly. Tighter for more preload and a reduction in sag, and the opposite for less. Every full rotation usually changes the sag by about 2 to 3mm, but this will vary depending on spring rate and thread pitch on the shock body. Adjust and measure rider sag again.

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Thanks to Maxima Racing Oils
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Thanks to Answer Racing
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Videography/edit/photography: Bert Beltran

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