To calculate dirt bike sag, you need to determine race sag and free sag using the following formulas:

1. Race Sag Formula

Race sag is how much the suspension compresses when the rider is on the bike. Race Sag=Bike Unloaded−Bike Loaded (with rider)\text{Race Sag} = \text{Bike Unloaded} – \text{Bike Loaded (with rider)}Race Sag=Bike Unloaded−Bike Loaded (with rider)

2. Free Sag Formula

Free sag is how much the suspension compresses under the bike’s own weight, without the rider. Free Sag=Bike Unloaded−Bike Loaded (no rider)\text{Free Sag} = \text{Bike Unloaded} – \text{Bike Loaded (no rider)}Free Sag=Bike Unloaded−Bike Loaded (no rider)

Steps to Measure:

1. Bike Unloaded (A): Measure from the rear axle to a fixed point on the fender with the bike on a stand (wheel off the ground).
2. Bike Loaded (no rider) (B): Measure the same point with the bike on the ground, under its own weight.
3. Bike Loaded (with rider) (C): Measure with the rider fully geared up in a natural riding position.

Example Calculation

• A (Unloaded): 600mm
• B (Bike only): 580mm
• C (Bike + Rider): 520mm

Race Sag

600mm−520mm=80mm600mm – 520mm = 80mm600mm−520mm=80mm

Free Sag

600mm−580mm=20mm600mm – 580mm = 20mm600mm−580mm=20mm

Recommended Sag Settings

• Race Sag: ~30-35% of total suspension travel (usually 90-105mm for dirt bikes).
• Free Sag: ~5-10% of total travel (typically 25-45mm).

If the race sag is too high → Increase preload.
If the race sag is too low → Decrease preload.

How to Set Dirt Bike Sag: Easy Guide for Beginners

Sag is one of the most important things on a dirt bike. It controls how the bike rides and feels on the track or trail. Getting it right can help you go faster, feel safer, and ride longer without getting tired. In this guide, you’ll learn what sag is, how to set it, and why it matters. Don’t worry, we’ll keep it super simple. No fancy words. No long sentences. Just clear steps and real talk.

What Is Sag?

Sag is how much your bike squats down when you sit on it. Every dirt bike needs the right amount of sag. If the bike sits too low or too high, it won’t handle right. It might feel bouncy, stiff, or even scary. Sag changes how the rear shock works. That shock controls how the back of your bike moves over bumps.

There are two types of sag. Static sag and rider sag. Static sag is how far the bike sinks under its own weight. Rider sag is how far the bike drops when you sit on it in your gear. Both are easy to check.

Why Is Sag So Important?

A bike with wrong sag won’t handle well. It can slide out in turns. It can kick you over the bars. It can feel too soft or too stiff. Getting it right helps the bike feel balanced and smooth.

Think about this. Imagine riding a bumpy trail. Your rear wheel needs to move up and down to follow the ground. If the sag is too little, the shock stays stiff. The rear tire won’t follow the ground. You’ll lose grip. If the sag is too much, the shock bottoms out. You’ll feel every bump like a hammer.

The right sag lets your shock move in both directions. That keeps your tire on the ground. More grip. More control. Less pain.

What You Need to Measure Sag

You don’t need many tools. A friend can help too.

Here’s what you need:

• A tape measure (just a normal one)
• A pen or marker
• A notepad or phone to write numbers
• A stand to lift your bike

Some bikes have a sag line marked already. If not, draw one near the rear fender, right above the axle. Use that same mark every time you measure.

Step 1: Lift the Bike and Measure

Put your bike on a stand. Let the rear wheel hang in the air. No weight on it at all. Now measure from the center of the rear axle to your mark above it. This is your full length. Write that number down.

Let’s say it reads 61.5 centimeters. That’s your baseline.

Step 2: Measure Static Sag

Now take the bike off the stand. Let it rest under its own weight. No one sits on it. Just let it settle.

Now measure from the same place again. From axle to mark. Let’s say it now reads 58 centimeters.

Take the first number and subtract the second. So:

61.5 cm – 58 cm = 3.5 cm, or 35 millimeters.

That is your static sag.

Most bikes need 35–45 millimeters. Some are a little different. Check your bike’s manual or start with 35mm if unsure.

Step 3: Measure Rider Sag

Now sit on the bike in full gear. Sit like you ride. Feet on the pegs. Hands on the bars. Back straight. You might need a friend to hold the bike steady.

Measure again from axle to mark.

Say it now reads 51 centimeters.

61.5 cm – 51 cm = 10.5 cm, or 105 millimeters.

That is your rider sag.

Most bikes like 100–115 millimeters of rider sag. Again, check your manual, but 105 is a great place to start.

Step 4: Adjust the Spring

So, your numbers are off. That’s okay. Time to adjust the shock spring.

To do this, you must loosen the lock ring on the spring. It’s a big round nut. Use an Allen key if needed. Then, turn the adjuster ring to change spring tension.

Tighten it to make the spring stiffer. That means less sag. Loosen it to make the spring softer. That means more sag.

Always go slow. One turn can make a big change. After adjusting, take new measurements. Keep checking until both static and rider sag are in the right range.

Some people use a special tool from KTM. Others use a punch and hammer. Either way works.

What Happens If Sag Is Wrong?

If sag is too small, the bike feels high and stiff. You’ll bounce around. The back wheel won’t grip well. You might feel like the bike pushes through turns.

If sag is too big, the rear end sags too low. The bike bottoms out easy. The front end feels light. The bike might turn too fast or feel twitchy.

You want the bike to stay level. Not too high. Not too low. Just right.

Every Bike Is Different

Your bike has its own numbers. KTM 450 XCF likes 35mm static and 105mm rider sag. Other bikes might need more or less. That’s okay. Just check your manual. Or ask someone who knows your bike.

Also, rider weight matters. A small rider needs less spring force. A heavier rider needs more. That’s why testing is so important.

Don’t Forget These Tips

Always measure from the same place. Always use the same mark. Always sit the same way on the bike.

Check sag often. Springs settle over time. You might need to tweak it now and then.

Ride with your gear on. Your weight changes the bike. Always check sag with full riding clothes, helmet, boots, and all.

Testing is the only way to feel what works. Ride. Adjust. Ride again.

How Sag Affects Speed

Some riders think sag is a small thing. But it’s not. It changes everything.

A bike with perfect sag feels smooth. You can push harder. Take faster lines. Jump safer. Land softer. Turn sharper. All because the shock is working right.

Bad sag? You fight the bike. You waste energy. You ride slower. It’s not fun.

So take the time. Measure. Adjust. Test. It’s worth it.

How Long Does It Take?

The whole job takes maybe 30 minutes. Less if you’ve done it before. It’s easy once you understand it.

Do it right before a race or ride. It makes a big difference. Trust the numbers. Trust the feel.

What If You Change Tires?

Good question. If your new tire is taller or shorter, sag changes. Always recheck after a tire change. Same goes for changing wheels or suspension parts.

Is There a Best Sag Number?

Not really. There’s a good range. But your style matters too. Some riders like more sag. Others like less. Start in the middle. Adjust from there.

Try 105mm rider sag and 35mm static sag. Ride. Then try 110mm rider sag. Ride again. Pick what feels better.

Trust your feel, not just numbers.

Should You Do This Alone?

You can. But it’s easier with help. One person holds the bike. One person measures. That way you sit right, and the bike stays straight.

You can measure alone with some tricks. Like leaning the bike on a wall. But it’s better with a buddy.

Final Thoughts

Sag is simple. It’s not magic. It’s just numbers. But those numbers matter. They control how your bike moves, feels, and handles.

Learning how to set sag is one of the first steps in bike setup. It’s something every rider should know. It doesn’t need special tools. Just a tape measure, a mark, and a little time.

Ride safe. Ride smart. Set your sag right. Feel the difference on your next ride.

And always test. Always ride. Always learn.

Got questions? Ask your local shop. Or message other riders online. Dirt bike riders help each other out.

Enjoy the ride. Keep it simple. And remember—sag first, speed later.