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How To Set The Sag On A Dirt Bike: A Step-By-Step Guide
Sag is a key part of your dirt bike’s suspension setup. What is sag? It is simply how much the suspension compresses under its own weight and under the rider’s weight. Setting the sag correctly is one of the most important things you can do for proper dirt bike suspension tuning. Can I set the sag myself? Yes, you absolutely can, and this guide will show you how. Getting the sag right helps your bike handle bumps better, turn more easily, and feel stable. This makes riding safer and more fun. Setting the sag involves a simple motorcycle sag adjustment, mainly focusing on setting motorcycle preload on the rear shock, and it’s a basic step in dirt bike suspension setup that every rider should know.
The Point of Setting Sag
Why do we need to set sag? It’s about getting the suspension into the best part of its travel. Think of suspension like a spring. If it’s pushed down too much (too soft sag), it hits the bottom easily on bumps. If it’s not pushed down enough (too stiff sag), it can’t stretch into dips or stay on the ground.
Correct sag allows the wheel to move up into its travel to soak up bumps and move down to follow the ground in dips. This helps the tires stay in touch with the dirt. Good tire contact means more grip for cornering, braking, and power.
Setting sag is the first step in dirt bike suspension tuning. It sets the baseline. Until sag is right, other adjustments like compression or rebound clickers won’t work as they should. It’s the foundation of a good dirt bike suspension setup.
Two Types of Sag
There are two main types of sag we measure on a dirt bike:
- Static Sag (or Free Sag): This is how much the bike’s own weight compresses the suspension. We measure this with the bike standing on its wheels but with no rider on it. Measuring static sag tells us if the spring rate is close to being right for the bike’s weight.
- Rider Sag (or Race Sag): This is how much the suspension compresses with the rider fully geared up and sitting on the bike in a normal riding position. Measuring rider sag is the most critical step. It tells us if the spring rate and preload are right for the rider’s weight. This is the number we adjust preload to get right.
Getting Ready to Measure Sag
You will need a few things to measure and set sag:
- Your dirt bike. Make sure it is clean so you can see the parts easily.
- Your full riding gear (helmet, boots, pants, jersey, chest protector, hydration pack if you use one). You need to measure sag with the weight you’ll actually be riding with.
- A friend to help you. It’s very hard to measure sag accurately by yourself.
- A long measuring tape. A metal one that stays stiff is best. Some shops sell special sag tools.
- Tools to adjust the rear shock preload. This usually means a large spanner wrench (or C-spanner) that fits the lock rings on the shock. Check your bike’s manual.
- Something to lift the bike so the rear wheel hangs freely. A bike stand or a milk crate works.
Make sure your bike’s suspension is working smoothly. If the shock is sticky or the linkage needs grease, fix that first. Setting sag on sticky suspension won’t work right.
Finding Your Measurement Points
You need two points to measure sag: one on the rear axle and one directly above it on the rear fender or chassis. These points must stay the same every time you measure.
- Lower Point: A common spot is the center of the rear axle bolt. Or you can pick a marked spot on the swingarm right at the axle.
- Upper Point: Pick a fixed point straight up from your lower point on the rear fender or a frame part. Mark it with a sticker or pen so you use the exact same spot every time.
It’s super important that these points are in a straight line up and down and stay the same. If you change points, your measurements won’t compare correctly. Measuring dirt bike sag depends on these fixed points.
The Steps: Measuring Static Sag
Static sag is the first measurement, but it doesn’t need adjusting directly. It helps check if your spring rate is suitable after you set rider sag.
Here is how to measure static sag:
h4 Step 1: Lift the Bike
Put your dirt bike on a stand or crate so the rear wheel is completely off the ground. The suspension should be fully extended.
h4 Step 2: Take Measurement 1 (M1)
With the suspension fully extended, measure the distance between your two chosen points (axle to fender). This is your first measurement, M1. Write this number down right away!
h4 Step 3: Bike on Wheels, No Rider
Take the bike off the stand. Let it stand upright on its wheels. Do not sit on it. Hold it steady so it is balanced.
h4 Step 4: Bounce the Bike
Gently push down on the rear of the bike a few times. Let it rise back up slowly. This helps the suspension settle naturally. Avoid bouncing it hard.
h4 Step 5: Take Measurement 2 (M2)
With the bike settled and standing on its own weight, measure the distance between your two chosen points again. This is your second measurement, M2. Write it down.
h4 Step 6: Calculate Static Sag
Your static sag is M1 minus M2.
- Static Sag = M1 – M2
For example, if M1 was 600mm and M2 was 590mm, your static sag is 10mm.
Write this static sag dirt bike number down. We will look at it again after setting rider sag. How to measure static sag is simple once you have M1.
The Steps: Measuring Rider Sag
This is the most important measurement. It tells you if the shock spring preload is right for your weight.
Here is how to measure rider sag:
h4 Step 1: Bike on Wheels, Rider Ready
Take the bike off the stand. Have your friend hold the bike steady so you can get on safely.
h4 Step 2: Get on the Bike in Full Gear
Put on all your riding gear. Get on the bike. Put your feet on the pegs. Sit in your normal riding position. Look forward, not down at the suspension.
h4 Step 3: Take Measurement 3 (M3)
This is where your friend helps. Your friend needs to measure the distance between your two chosen points (axle to fender) while you are sitting on the bike.
It is best for your friend to take three measurements:
- Push down gently on the rear fender and let it rise slowly to the measurement point. Write it down.
- Lift up gently on the rear fender and let it settle slowly to the measurement point. Write it down.
- The average of these two numbers is your M3. (Add the two numbers and divide by 2).
This helps avoid sticky suspension from giving a wrong number. This is how to measure rider sag accurately.
h4 Step 4: Calculate Rider Sag
Your rider sag is M1 minus M3.
- Rider Sag = M1 – M3
Using our example where M1 was 600mm: If your M3 was 500mm, your rider sag is 600mm – 500mm = 100mm.
This rider sag measurement is the key number you need to adjust.
Setting the Sag: Adjusting Preload
Now that you have your rider sag number, you need to compare it to the target number for your bike. The target number is usually in your bike’s owner’s manual or service manual. If you don’t have the manual, a common starting point for rider sag on many modern dirt bikes is around 100mm to 110mm for motocross and slightly more (like 105mm-115mm) for off-road or trail riding, but ALWAYS check your manual first.
h4 What the Rider Sag Number Tells You
- Rider Sag is too low (less than target, e.g., 90mm when target is 100mm): The suspension is too stiff for your weight. You need to make the spring softer by reducing the preload.
- Rider Sag is too high (more than target, e.g., 115mm when target is 100mm): The suspension is too soft for your weight. You need to make the spring stiffer by increasing the preload.
h4 Adjusting the Rear Shock Preload
Setting motorcycle preload means changing how much the spring is squeezed when the suspension is fully extended (M1 position).
Most dirt bike rear shocks have two large nuts (lock rings) at the top of the spring.
- Lower ring: This one sits right on top of the spring.
- Upper ring: This one is a lock nut, it holds the lower ring in place.
Here is how to adjust them:
h5 To Increase Preload (Make Sag Number Lower):
This is needed if your rider sag is too high (suspension is too soft). You are squeezing the spring more.
- Use a punch or screwdriver and a hammer to gently tap the upper lock ring counter-clockwise. This loosens it. Be careful not to damage the shock body.
- Use the spanner wrench or punch to turn the lower ring clockwise. This pushes the ring down and compresses the spring more. Turn it a little bit at a time (maybe a couple of full turns).
- Tighten the upper lock ring against the lower ring to lock them in place. Tap it gently clockwise.
h5 To Decrease Preload (Make Sag Number Higher):
This is needed if your rider sag is too low (suspension is too stiff). You are letting the spring expand a little.
- Use a punch or screwdriver and a hammer to gently tap the upper lock ring counter-clockwise to loosen it.
- Use the spanner wrench or punch to turn the lower ring counter-clockwise. This lets the spring expand. Turn it a little bit at a time.
- Tighten the upper lock ring against the lower ring to lock them in place. Tap it gently clockwise.
h4 Re-Measure and Repeat
After making an adjustment, you MUST measure the rider sag again.
- Lift the bike to get M1 again (or use your previous M1 if you are sure the bike fully extended).
- Get back on the bike in full gear with your friend.
- Take M3 again (the average of the up and down measurements).
- Calculate your new rider sag (M1 – M3).
Keep adjusting and re-measuring until your rider sag is within the target range given in your bike’s manual (e.g., 100mm +/- 5mm).
Making even small changes to the preload rings can make a big difference to the sag number. Adjust slowly and check often. This is part of the motorcycle sag adjustment process.
Grasping Static Sag After Setting Rider Sag
Once your rider sag is set correctly using the preload adjusters, look at your static sag number again.
Remember, static sag is M1 – M2 (fully extended length minus bike-on-its-own-weight length).
- Ideal Static Sag: For most bikes, with rider sag set correctly, the static sag should be in a specific range, often around 30mm to 40mm. Check your manual for the exact number.
- Static Sag too low (less than target, e.g., 15mm when target is 30-40mm): This usually means the shock spring is too stiff for your weight. You had to add a lot of preload to get the rider sag right, and now the bike doesn’t sag much under its own weight. The bike might feel harsh.
- Static Sag too high (more than target, e.g., 50mm when target is 30-40mm): This usually means the shock spring is too soft for your weight. You had to take away a lot of preload (or couldn’t even get enough preload) to get the rider sag right, and now the bike sags too much under its own weight. The bike might feel bouncy or bottom out easily.
If your static sag is outside the recommended range after setting rider sag correctly, it’s a strong sign you need a different spring rate for the rear shock. A spring that matches your weight and riding style is crucial for proper dirt bike shock adjustment and overall performance. Setting sag only works correctly if the spring rate is close to right for you.
What About Fork Sag?
While rear sag is the most critical and commonly adjusted, the front forks also have sag. Fork sag is measured in a similar way:
- Lift the front wheel off the ground. Measure from the dust seal up to the bottom of the triple clamp (M1).
- Put the bike on its wheels. Gently push down on the front and let it settle. Measure again (M2). Static fork sag = M1 – M2.
- Sit on the bike in riding position. Have a friend measure again (M3). Rider fork sag = M1 – M3.
Fork sag is usually adjusted by changing the spring preload inside the forks or changing the springs themselves. This is more complex and often involves disassembling the forks. For most riders, setting the rear sag correctly is the priority and provides the biggest handling improvement. Front sag is part of full dirt bike suspension setup, but start with the rear.
Target Sag Numbers
Again, check your bike’s manual first! But here are some general target ranges. These are just starting points and can vary slightly based on bike type and rider preference.
| Sag Type | Bike Type | Common Target Range |
|---|---|---|
| Rider Sag | Motocross (MX) | 100mm – 105mm |
| Rider Sag | Off-Road/Trail | 105mm – 115mm |
| Static Sag | All Dirt Bikes | 30mm – 40mm |
Note: These are general ranges. Your specific bike’s manual might have different numbers. Always use your manual’s recommendations.
If you cannot reach these numbers even with full preload adjustment, you likely need a new spring.
Important Sag Setting Tips
- Wear All Your Gear: This adds weight and changes the sag. Do not measure in street clothes.
- Get a Friend: Measuring sag accurately by yourself is nearly impossible. Your friend needs to hold the bike and take the measurements.
- Use Consistent Points: Mark your measurement spots on the axle and fender so you always use the same ones.
- Bounce Gently: This helps the suspension settle and gives a more accurate measurement (especially for the M3 average).
- Write Numbers Down: Keep track of your M1, M2, M3, calculated static sag, and calculated rider sag. Note any adjustments you make.
- Check Your Manual: Seriously, check your bike’s manual for the recommended sag numbers and adjustment steps.
- Measure Often: Sag can change over time as springs settle or wear. Re-check your sag every few rides, especially after suspension service.
- Sag is Just the Start: Setting sag is the first step in proper dirt bike suspension tuning. Once sag is right, you can adjust compression and rebound clickers to fine-tune the feel. But sag must be set first.
Troubleshooting Sag Problems
h4 Cannot Get Enough Rider Sag (Too Stiff)
- You’ve taken all the preload off (lower ring is high on the shock body), but the rider sag number is still low (e.g., 90mm when you want 100mm).
- Your static sag is likely very low (e.g., 10-20mm).
- Problem: The shock spring is too stiff for your weight.
- Solution: You need a softer shock spring.
h4 Cannot Get Correct Rider Sag (Too Soft)
- You’ve added a lot of preload (lower ring is far down the shock body), but the rider sag number is still high (e.g., 115mm when you want 100mm).
- Your static sag is likely very high (e.g., 45-50mm+).
- Problem: The shock spring is too soft for your weight.
- Solution: You need a stiffer shock spring.
Getting the right spring rate is crucial for effective dirt bike suspension setup. Sag adjustment helps fine-tune the spring you have, but it can’t fix a totally wrong spring rate. If you need a new spring, consult your bike’s manual or a suspension expert to find the correct rate for your weight and riding style.
Deciphering the Sag Numbers
Understanding what static sag and rider sag tell you together is important.
- Rider Sag is key: This is the first thing to set using preload. It puts you in the right part of the suspension travel.
- Static Sag confirms the spring: Once rider sag is right, static sag tells you if the spring rate is appropriate.
- Low static sag with correct rider sag = spring likely too stiff.
- High static sag with correct rider sag = spring likely too soft.
- Correct static sag with correct rider sag = spring rate is probably right for you.
This check using static sag after setting rider sag is vital. It helps you know if you just need to adjust preload or if you need a different spring altogether for proper motorcycle sag adjustment.
Sag Setting and Overall Performance
Setting sag isn’t just a number game. It greatly impacts how your bike rides.
-
Too Little Sag (Too Stiff):
- Bike feels harsh over small bumps.
- Front wheel might push in corners.
- Bike feels tall.
- Rear wheel may not follow the ground well in dips, losing traction.
- Static sag is low.
-
Too Much Sag (Too Soft):
- Bike feels mushy or wallows.
- Bike sits low in the travel, bottoming out easily.
- Front wheel might feel light in corners.
- Bike feels short and might kick up over jumps or bumps.
- Static sag is high.
Getting the sag correct makes the bike feel balanced. It lets the suspension work across its full range of movement. This improves tire grip, stability, and how the bike turns. It’s a fundamental part of any dirt bike suspension tuning or dirt bike suspension setup.
Fathoming the Importance of Accurate Measurement
Every millimetre matters when setting sag. Using precise measurements is vital.
- Use the right tools: A proper measuring tape or sag tool is best.
- Be consistent: Always measure from the exact same points.
- Take multiple readings: Averaging the ‘up’ and ‘down’ M3 helps avoid errors from suspension stiction.
- Have a helper: This makes the process much easier and more accurate.
Poor measurements lead to setting the sag wrong. This means all the effort you put in might make the bike ride worse, not better. Take your time and measure carefully. Measuring dirt bike sag correctly is the key first step.
Steps Recap for Setting Sag
- Measure M1: Bike lifted, wheel off ground. Measure from axle to fender point.
- Measure M2: Bike on wheels, no rider. Settle suspension. Measure from axle to fender point. Calculate Static Sag (M1 – M2). Note this for later.
- Measure M3: Rider in full gear on the bike, feet on pegs. Have a friend take three measurements (press down and release, lift up and release, average the two). This is your M3.
- Calculate Rider Sag: Rider Sag = M1 – M3.
- Compare to Target: See if your rider sag is within the range in your bike’s manual.
- Adjust Preload: If sag is off, adjust the shock’s preload rings.
- Increase preload (squeeze spring more) if rider sag is too high (too soft).
- Decrease preload (let spring expand) if rider sag is too low (too stiff).
- Re-Measure Rider Sag: Go back to step 3 and repeat until rider sag is correct.
- Check Static Sag: Once rider sag is correct, look at your static sag number (M1 – M2). Is it in the recommended range?
- Evaluate Spring Rate: If static sag is outside the range with correct rider sag, you likely need a different spring.
- Note Settings: Write down your final sag numbers and perhaps how many turns you adjusted the preload.
This motorcycle sag adjustment process needs care but pays off hugely in how your bike performs. Setting motorcycle preload is the direct way to change sag.
Frequently Asked Questions (FAQ)
h4 How often should I check my sag?
Check your sag before riding season starts and every few rides after that. Springs can settle, and checking ensures your setup stays right. Always check after working on the rear suspension.
h4 Can I just use a sag scale tool?
Yes, sag scales or specific sag tools can make measuring easier and quicker, but the principle is the same. You still need M1 and M3 (or M2) measurements.
h4 Does changing sag affect my suspension clicker settings?
Yes, it does. Changing sag changes where the suspension rides in its stroke. This changes how the compression and rebound damping will feel. Set sag first, then adjust clickers.
h4 What if my bike manual doesn’t give sag numbers?
While rare for modern bikes, if you can’t find the numbers, the general ranges (100-105mm for MX, 105-115mm for off-road rider sag, 30-40mm static sag) are common starting points. However, getting the bike’s manual is highly recommended. Contacting the bike maker or a suspension shop can also help.
h4 Can I set sag without help?
It’s very difficult to get an accurate measurement by yourself. You need someone to hold the bike steady and take the measurements while you are sitting on it naturally. It’s a two-person job for best results.
h4 My bike feels okay, do I still need to set sag?
Setting sag correctly is the baseline for good handling. Your bike might feel okay, but setting sag properly can unlock its true potential and improve safety and comfort. It’s worth the effort.
h4 What if I’m between spring sizes?
If you are right on the edge between recommended spring rates for your weight, consult a suspension expert. Your riding style and the specific bike model can influence which spring might be better. Minor preload adjustments can fine-tune, but you need to be on the right spring first.
In Closing
Setting the sag on your dirt bike is a fundamental step in proper dirt bike suspension setup and dirt bike suspension tuning. It ensures your suspension works in the right part of its travel, giving you better control, more grip, and a safer ride. By following these steps for measuring dirt bike sag, adjusting motorcycle sag adjustment by setting motorcycle preload, and checking both static sag dirt bike and rider sag measurement, you can make a big difference in your bike’s performance. Don’t skip this vital task. Get your gear on, grab a friend, and set that sag!