OBERSON BUYING GUIDE
How to Adjust Your Mountain Bike Suspension
Oberson’s experts explain how to adjust sag, progression, and rebound to set up your mountain bike suspension for more comfort, grip, and control on the trails.
AT A GLANCE
Properly adjusted suspension will improve your bike’s performance and boost your confidence. This guide explains how to set sag, check progression, and adjust rebound. Spending a few minutes dialling in your suspension can make every ride more fun. If you ride a hardtail, simply follow the fork instructions and skip the rear-shock section.
Get Ready
Here’s what you need to do before adjusting your suspension:
Put on your normal riding gear, including your helmet, hydration pack, and anything else you typically carry.
Inflate your tires to your usual riding pressure.
Open any suspension lockouts.
Find a flat area without traffic.
Have a shock pump on hand and, if needed, a measuring tape.
Consult your suspension or bike manufacturer’s recommended settings if available.
Set Your Sag
Sag is the amount your suspension compresses under your weight when you’re in a normal riding position. Proper sag lets your bike absorb impacts and maintain traction.
You should usually aim for about 20% sag in the fork and 30% sag in the rear shock, but the exact percentages vary based on suspension designs and riding styles. Check your shock manufacturer’s recommendations.
Before taking any measurements, compress the fork and shock several times and let them settle for a few seconds. This helps the suspension find its normal operating position and ensures more accurate sag measurements.
Start with the rear shock, then move on to the fork.
Rear Shock
- Move the O-ring against the shock body.
- Ensure the shock setting is fully open.
- Carefully sit on the bike in a normal riding position.
- Lift your feet off the ground so your full weight is supported by the bike.
- Gently step off the bike without moving the O-ring.
- Check the O-ring against the sag percentages on the shock body or stanchion. If the percentages aren’t displayed, measure the amount of sag, and compare it to the manufacturer’s recommendation.
- Add or remove air as needed.
After each pressure adjustment, compress the shock several times before measuring sag again. Repeat the process until you reach the desired setting.
As noted above, most riders should measure rear-shock sag while seated. However, more aggressive riders may prefer to check sag in a standing position because this more closely reflects how they ride on the trail. If you choose this method, have someone hold the bike.
Fork
Many manufacturers provide recommended air-pressure settings based on rider weight. You can use these recommendations as a starting point and then, if desired, verify the setting by measuring sag. If weight and sag percentage recommendations aren’t provided, simply follow the procedure below.
- Move the O-ring against the fork seal.
- Ensure that the front suspension isn’t locked out.
- Stand on the pedals while holding the handlebars and rolling forward.
- Gently settle into the suspension without bouncing.
- Gradually slow down and carefully step off the bike.
- Measure the amount of sag and compare it to the manufacturer’s recommendation.
- Add or remove air as needed.
As with the rear shock, compress the fork several times after each pressure adjustment before measuring sag again.
Riders who prioritize pedalling efficiency and support may prefer slightly less sag. Riders seeking maximum traction and control on rough terrain may prefer slightly more. Start with the manufacturer’s recommendation and make small adjustments from there.
Check Your Progression
Once you’ve set your sag, it’s time to make sure you’re using the suspension’s travel effectively.
Progression describes how resistant your suspension becomes near the end of its travel. Sag is related to rider weight, and progression is a measure of the forces applied to the bike. While sag determines how much the suspension compresses under your weight, progression affects how it behaves deeper in its travel as you push into it when absorbing larger impacts.
To get a rough idea of whether your progression is dialled in, roll slowly on a flat surface in a neutral standing position and bounce the suspension as hard as possible without leaving the ground. Test the fork and shock separately.
After each test, check the position of the O-ring. The closer it is to the end of the stanchion or shock shaft, the more travel you’ve used. During this test, the rear shock should use approximately 90% of its travel. The fork should use approximately 80–90% of its travel without bottoming out.
Next, ride a familiar trail and check the O-rings again. Your suspension should occasionally use most of its travel on larger impacts without bottoming out frequently.
If your suspension bottoms out regularly despite having the correct sag, you may need more progression. If you’re not using most of your suspension travel, you may need less.
Progression is typically adjusted with volume spacers installed inside or removed from the fork or shock. Adding a volume spacer makes the suspension more resistant to bottoming out near the end of its travel. Removing a volume spacer makes it easier to use full travel.
If you’re comfortable working on your suspension, consult the manufacturer’s instructions for adding or removing volume spacers. Otherwise, a qualified bike shop can help determine the right setup for your riding style and terrain.
If you’d rather not install or remove volume spacers, a small compromise in sag is often a practical solution. Adding a little air pressure can help reduce bottom-outs, while reducing pressure slightly can make it easier to use full travel. Keep in mind that this affects the entire suspension stroke rather than just the end of the travel.
| If… | Likely Cause | Try This |
|---|---|---|
| You bottom out frequently despite correct sag. | Progression is too low. | Add a volume spacer. Alternatively, add a small amount of air pressure. |
| You’re not using most of your travel despite correct sag. | Progression is too high. | Remove a volume spacer. Alternatively, reduce air pressure slightly. |
| Adding pressure fixes bottom-outs but makes the ride harsh. | Progression may be too low. | Consider adding a volume spacer instead of more pressure. |
| Reducing pressure helps use more travel but makes the bike feel too soft. | Progression may be too high. | Consider removing a volume spacer instead of lowering pressure further. |
Adjust Your Rebound
Rebound damping controls how quickly your suspension returns after being compressed. The goal is to allow the suspension to recover quickly enough to absorb repeated bumps. If it’s set too fast, the bike can feel nervous or bouncy. When the rebound is too slow, the suspension won’t recover quickly enough between impacts, reducing traction and control.
Rebound adjusters are often marked with tortoise and rabbit symbols or + and − signs. In most cases, moving toward the tortoise or + increases rebound damping and slows the rebound speed, while moving toward the rabbit or − decreases damping and speeds up the rebound. If you’re unsure, consult your suspension manufacturer’s documentation.
Rear Shock
Turn the rebound adjuster to its slowest setting. Then, ride slowly off a curb while seated on the bike. Gradually increase the rebound speed one click at a time and repeat the test.
The ideal setting is usually the fastest rebound speed that causes the shock to slightly overshoot its sag position before settling back down.
Fork
Turn the rebound adjuster to its slowest setting. While standing over the bike, compress the fork through roughly one-third of its travel and release it suddenly. Increase the rebound speed one click at a time, repeating the test until the front wheel barely comes off the ground. Then turn the rebound back one click.
Final Check for Balance
Repeatedly load and unload the suspension in a standing position while rolling over flat ground. The fork and shock should feel balanced and return at similar speeds. If there’s a slight imbalance, it’s better for the fork to rebound slightly faster than the rear shock. The other way around, the suspension can project the rider forward when taking big hits. Once you’re on the trail, make small adjustments as needed.
Troubleshooting Common Suspension Problems
Even after following the steps above, you may want to fine-tune your suspension. Use the chart below to identify common issues and possible solutions.
| If… | Possible Cause | Try This |
|---|---|---|
| Your rear shock or fork bottoms out frequently. | Spring rate or progression is too low. | Add a small amount of air pressure. If that makes the suspension harsh over small bumps, consider adding a volume spacer. |
| You’re not using most of your suspension travel. | Spring rate or progression is too high. | Reduce air pressure slightly. If the suspension still won’t use most of its travel, consider removing a volume spacer. |
| Your suspension feels harsh over small bumps. | Air pressure or progression may be too high. | Reduce air pressure slightly or consider removing a volume spacer. |
| Your fork dives excessively when braking or on steep terrain. | Fork air pressure may be too low. | Add a small amount of air pressure and test again. |
| The bike feels bouncy after impacts. | Rebound is too fast. | Increase rebound damping by moving the adjuster toward the tortoise or + setting. |
| The suspension feels sluggish or doesn’t recover quickly between bumps. | Rebound is too slow. | Reduce rebound damping by moving the adjuster toward the rabbit or − setting. |
| The bike feels unstable because the front and rear suspension react differently. | Rebound settings may be unbalanced. | Compare front and rear rebound speeds and make small adjustments until the bike feels balanced. |
FAQ — How to Adjust Mountain Bike Suspension
What tools do you need to adjust mountain bike suspension?
You’ll need a shock pump. A measuring tape can also be helpful when checking sag on forks or shocks that don’t display sag percentages.
What do the tortoise and rabbit symbols mean on a fork or shock?
These symbols indicate rebound damping. Moving the adjuster toward the tortoise slows the rebound speed. Moving it toward the rabbit speeds it up. A slower rebound can improve control on bigger impacts, and a faster rebound helps the suspension recover more quickly between bumps.
Why am I not using all of my suspension travel?
If you’re not using most of your suspension travel on large impacts, your air pressure or progression may be too high.
Start by checking your sag. If it’s within the manufacturer’s recommended range, you can try reducing air pressure slightly. If that improves use of the travel but the suspension feels too soft, you may benefit from removing a volume spacer.
Keep in mind that it’s normal to have some travel remaining after most rides. The goal is to use most of your travel on larger impacts without bottoming out frequently.
Why does my suspension feel harsh over small bumps?
Suspension that feels harsh over roots, rocks, and small bumps probably has too much air pressure or too much progression.
Start by checking your sag. If it’s within the recommended range, try reducing air pressure slightly. If the suspension still feels harsh and you’re not using most of the available travel, you may benefit from removing a volume spacer.
Can I use a regular tire pump to adjust mountain bike suspension?
No, mountain bike forks and shocks require much higher pressures than tires, and a regular floor pump isn’t designed to measure or deliver those pressures accurately.
To adjust sag and air pressure correctly, you’ll need a shock pump. These pumps are designed for suspension and feature a gauge that allows for precise adjustments.
Should I adjust sag or rebound first?
Start with sag. Sag determines where your suspension sits in its travel when you’re in a normal riding position. If your sag is incorrect, it’s hard to evaluate any other suspension adjustment.
Once sag is dialled in, adjust rebound damping. Rebound controls how quickly the suspension returns after being compressed, and the ideal setting depends on how much air pressure and sag you’re running.
Oberson’s Repair Shop
Not sure your suspension is set up correctly? Our bike technicians can help dial in your suspension and keep your bike performing at its best. Visit us in Laval or Brossard for expert bike maintenance.
