Dirt Bike Sag Calculator: Instantly Measure & Set Your Suspension Sag

Proper suspension sag is the most critical adjustment for your dirt bike’s handling. Incorrect sag can lead to dangerous handling characteristics, poor traction, and an uncomfortable ride. Whether you’re a motocross racer or a trail rider, setting your sag correctly is the first and most important step in suspension tuning.

This dirt bike sag calculator and guide makes professional suspension setup easy for riders of all levels, helping you unlock your bike’s true potential.

What is Sag in Dirt Bike Suspension?

Sag is the amount your suspension compresses under the bike’s weight and the rider’s weight. It’s the difference between your suspension fully extended and at rest. There are two key types of sag:

• Static Sag (or Free Sag): The amount the suspension compresses under the bike’s own weight. This tells you if your spring rate is correct for your weight.
• Race Sag (or Rider Sag): The amount the suspension compresses with the rider in full gear in a riding position. This is the primary measurement for setting up your bike’s handling.

Why Correct Sag Matters:

• Balanced Handling: Proper sag ensures your bike corners, turns, and tracks predictably.
• Optimal Traction: Correct sag keeps the tire in contact with the ground for maximum grip.
• Safety: Prevents dangerous handling issues like headshake or wallowing.
• Comfort: Absorbs impacts effectively, reducing rider fatigue.

For most dirt bikes, the target Race Sag is 100-105mm (about 4 inches), which is roughly 30-35% of the rear wheel’s total travel. Static Sag should typically be between 25-40mm.

How to Measure Dirt Bike Sag

Tools Needed: Tape measure, a stand (like a crate or bike stand), and an assistant.

Step-by-Step Measurement:

1. Measure Fully Extended Length: Place the bike on a stand so the rear wheel is off the ground. Measure from the axle vertically up to a fixed point on the fender or subframe. Record this as “Fully Extended.”
2. Measure Race Sag: Have the rider (in full gear) sit on the bike in a normal riding position, feet on the pegs. Have your assistant hold the bike upright. Gently push down on the rear and let it extend back up slowly. Measure from the same points. Record this as “Rider On.”
3. Measure Static Sag: Take the bike off the stand and let it sit under its own weight. Without the rider, push down and let it settle. Measure from the same points. Record this as “Bike Only.”

Example Numbers:

• Fully Extended: 600mm
• Rider On: 500mm
• Bike Only: 575mm
• Race Sag = 600 – 500 = 100mm (Perfect!)
• Static Sag = 600 – 575 = 25mm (Good!)

Ideal Sag Settings for Different Dirt Bikes

Common Sag-Related Problems & Adjustments

Problem: Too Much Race Sag (>110mm)

• Symptoms: Bike feels wallowy and vague; front end pushes in corners; prone to headshake.
• Fix: Increase spring pre-load by tightening the shock collar.

Problem: Too Little Race Sag (<95mm)

• Symptoms: Harsh ride; rear wheel kicks up on bumps; poor traction; bike feels tall.
• Fix: Decrease spring pre-load by loosening the shock collar.

Troubleshooting Your Spring Rate

• If Static Sag is too small (<15mm) after setting Race Sag: Your spring is too stiff. You’ve had to add too little pre-load, and the bike can’t settle under its own weight.
• If Static Sag is too large (>40mm) after setting Race Sag: Your spring is too soft. You’ve had to add excessive pre-load to achieve race sag, over-preloading the spring.

Conclusion

Ready to transform your bike’s handling? Use our dirt bike sag calculator above, grab your tools, and dial in your suspension in under 10 minutes. A perfectly set up bike is a game-changer.

Share your results or ask for setup advice in the comments below or in your favorite dirt bike forum!

Dirt Bike Suspension Sag FAQ

What is the difference between static sag and race sag?

Static sag (or free sag) is the amount the suspension compresses under the motorcycle’s own weight without a rider. This measurement helps determine if your spring rate is correct. Race sag (or rider sag) is the amount the suspension compresses with the rider in full gear in a normal riding position. This is the primary measurement used to set up your bike’s handling characteristics.

What is the best race sag for motocross?

For most motocross bikes, 100-105mm (approximately 4 inches) of race sag is the ideal starting point. This provides the perfect balance between cornering stability and bump absorption for track riding. Faster or heavier riders may prefer the tighter end of this range (100mm), while lighter riders might go slightly higher toward 105mm.

Can sag settings affect cornering or jumping?

Absolutely. Too much sag makes the bike squat excessively, causing the front end to feel light and push or understeer in corners. Too little sag makes the rear end stiff, causing it to kick on jump faces and lose traction when accelerating out of corners. Proper sag ensures balanced weight distribution for optimal cornering and stable jumping.

How often should I check my sag?

You should check your sag every 2-3 rides, or anytime you experience significant changes such as different riding gear, varying terrain conditions, or after a hard crash. Springs can also settle over time, so regular checks ensure your settings remain optimal for performance and safety.

What tools make sag measurement easier?

While a standard tape measure works adequately, a dedicated sag scale or sag ruler provides more accurate and consistent measurements. These specialized tools typically feature a hook for the axle and a pointer for the fender, allowing for easier one-person operation and more reliable results.

What if I can’t get both static and race sag measurements correct?

If you cannot achieve both proper static and race sag measurements simultaneously, it indicates your spring rate is incorrect. If static sag is too small when race sag is correct, your spring is too stiff. If static sag is too large when race sag is correct, your spring is too soft. In either case, you’ll need to replace your spring with the proper rate for your weight.

Does sag setting affect front suspension too?

While we primarily measure and adjust sag on the rear shock, the concept applies to front forks as well. Proper rear sag ensures balanced front-to-rear weight distribution, which directly affects how your front suspension works. Many professional riders also set fork sag, though it’s less commonly measured by recreational riders.

Should sag settings be different for different riding styles?

Yes, optimal sag settings vary by riding discipline. Motocross riders typically run 100-105mm for aggressive handling. Enduro and trail riders often prefer 105-115mm for better traction and obstacle absorption. Dual-sport riders might use 90-100mm for improved street manners. Always start with manufacturer recommendations and adjust for your preferences.

How does rider weight affect sag settings?

Rider weight directly determines the spring preload needed to achieve proper sag. Heavier riders require more preload (tighter spring collars) while lighter riders need less preload. If you cannot achieve proper sag within the adjustment range of your current spring, you need a different spring rate specifically suited to your weight.

Can I set sag by myself or do I need help?

While having an assistant makes the process easier, you can set sag alone using proper technique. Use a stand to get initial measurements, then carefully get into riding position while supporting yourself against a wall or stable object. Dedicated sag measurement tools specifically designed for one-person operation can be particularly helpful for solo work.