Setting sag is one of the most important steps in achieving a balanced, predictable, and high-performing mountain bike suspension setup. Whether you ride trail, enduro, XC, or e-MTB, sag determines how your bike behaves under your body weight and real-world terrain forces. Get it right, and the bike feels planted, supportive, and stable. Get it wrong, and even premium suspension will feel harsh, wallowy, or inconsistent.
In 2026, suspension technology is more refined than ever — from advanced air spring curves to adjustable volume spacers and ultra-sensitive damping circuits — but the foundation remains the same: proper sag is the starting point for every good suspension setup. This step-by-step guide walks you through the entire process, what numbers to aim for, how to measure accurately, and how to troubleshoot common setup issues.
Key Takeaways
- Sag sets the “starting point” of your suspension travel.
- Typical sag targets: 25–30% rear, 15–20% fork (trail/all-mountain).
- Proper sag improves traction, comfort, braking, and cornering.
- Air suspension is set via pressure adjustments; coil uses preload.
- You must wear full riding gear while setting sag.
- Consistency matters more than chasing exact numbers.
- Minor adjustments drastically change ride feel — start small.
1. What Is Sag and Why It Matters
Sag is the amount your suspension compresses under your static body weight. It determines how much travel remains available for bumps, impacts, braking forces, and traction needs.
Why Sag Matters
- Traction: More sag = better grip, especially in off-camber or chattery terrain.
- Stability: Too little sag makes the bike harsh and skittish; too much makes it wallowy.
- Geometry: Sag changes head angle, bottom bracket height, and wheelbase.
- Braking: Proper sag helps the suspension stay active under braking.
- Cornering: Balanced sag prevents understeer and oversteer.
Correct sag makes the bike predictable — and predictability makes you faster and safer.
2. What Sag Should You Run? (By Discipline)
Use these numbers as starting points. Adjust based on terrain and style.
Fork Sag
- XC: 10–15%
- Trail: 15–20%
- Enduro/FR: 20–25%
- E-MTB: 15–20% (to handle extra weight)
Rear Shock Sag
- XC: 20–25%
- Trail: 25–30%
- Enduro/FR: 28–33%
- E-MTB: 25–30%
Heavier riders or those who prefer aggressive descending may choose a bit more sag; lighter or efficiency-minded riders may run less.
3. Tools You Need
- Shock pump (with an accurate gauge)
- A friend or wall for support
- Measuring ruler or built-in O-ring indicator
- Riding gear (pack, shoes, water, tools — everything you carry)
Wearing gear is critical because sag is set based on real riding weight, not bathroom scale weight.
4. How to Set Fork Sag: Step-by-Step
Setting fork sag is usually easier because you can stay in a neutral standing position.
Step 1: Slide the O-ring down
Move the fork’s O-ring gently to the base of the stanchion. If there’s no O-ring, use a small zip tie.
Step 2: Get into attack position
Stand on the bike in your normal descending stance:
- Pedals level
- Knees slightly bent
- Weight centered
- Hands lightly on bars
Bounce gently a few times and let the suspension settle.
Step 3: Have a friend stabilize
Your helper holds the bike upright so you’re not using the bars to balance.
Step 4: Step off carefully
Avoid compressing the fork while dismounting. Move off the bike straight up or backward.
Step 5: Measure the sag
Measure how far the O-ring moved.
Example:
140 mm travel fork × 20% sag = 28 mm sag target
If your sag measurement is:
- Too deep → add air pressure
- Too shallow → remove air pressure
Make changes in small increments (~5–10 psi).
Step 6: Recheck after adjustments
Repeat until the fork reads your target sag.
5. How to Set Rear Shock Sag: Step-by-Step
Rear sag is more critical because it dramatically influences geometry and traction.
Step 1: Move the O-ring
Slide the shock’s O-ring against the seal.
Step 2: Sit or stand in riding position
Depending on your bike’s design:
- Trail bikes: sit upright in climbing position
- Aggressive/enduro bikes: stand in neutral attack position
- E-MTBs: sit (extra weight compresses evenly)
Bounce once or twice to settle.
Step 3: Have a friend hold the bike
Rear sag is impossible to measure accurately without support.
Step 4: Step off carefully
Avoid rocking the bike or compressing the shock further.
Step 5: Measure sag
A 50 mm shock stroke with 30% sag should compress 15 mm.
If sag is:
- Too deep → add air or increase preload (coil)
- Too shallow → reduce air or back off preload
For Coil Shocks
Preload should not exceed 2–3 full turns from zero preload.
If you exceed this, your coil spring rate is too soft.
6. Setting Sag on E-MTBs
E-MTBs weigh more and put different loads on suspension.
Key Considerations
- Aim slightly lower sag numbers (stiffening slightly helps support weight).
- Battery and motor weight affects shock leverage—expect to run higher pressures.
- E-MTBs benefit from balanced sag more than most bikes due to geometry influence.
Recommended sag:
- Fork: 15–20%
- Shock: 25–30%
7. Common Sag Problems & How to Fix Them
Problem: Bike feels harsh or skittish
Cause: Too little sag
Fix: Remove air pressure (fork and/or shock)
Problem: Bike feels sluggish or “wallowy”
Cause: Too much sag
Fix: Add air pressure or increase spring rate
Problem: Rear shock bottoms out frequently
Cause: Sag too high OR not enough volume spacers
Fix:
- Add air pressure
- Add volume spacers (if sag is already correct)
Problem: Front dives under braking
Cause: Too much fork sag
Fix: Increase fork pressure slightly
Problem: Bike understeers in corners
Cause: Rear too soft (too much sag)
Fix: Increase shock pressure
Problem: Bike oversteers or feels twitchy
Cause: Rear too firm or fork too soft
Fix: Adjust both gradually — aim for balance
8. Sag Balance: The Most Overlooked Setup Principle
Even perfect sag numbers won’t work if the balance between fork and shock is off.
Signs fork and shock are out of sync
- Front feels harsh but rear feels soft
- Bike see-saws when pumping terrain
- Traction inconsistent between wheels
Ideal balance guidelines
- If the fork sag increases, increase rear sag slightly
- If the shock is made firmer, add a bit of fork firmness too
Small changes keep the bike’s geometry consistent and handling predictable.
9. How Often You Should Check Sag
- New bike: every ride for the first week
- New shock/fork service: first 2–3 rides
- Regular use: once per month
- After major weight change: immediately
Modern air chambers can lose small amounts of pressure over time — this is normal.
10. Volume Spacers & Why They Matter (After Sag Is Set)
Sag sets where the suspension starts. Volume spacers control how it behaves deeper in travel.
More spacers = more progression
- Harder to bottom out
- More pop
- Better aggressive riding feel
Fewer spacers = more linear
- Softer midstroke
- Better small-bump sensitivity
- More traction focus
Always set sag first, then tune progression.
11. Final Ride Check: The Real Test
Once sag is set, evaluate the bike on your normal loop.
Look for:
- Consistent support in corners
- Smooth small-bump traction
- No unexpected wallow
- Balanced feel at high and low speeds
If anything feels off, adjust sag by 2–3% at a time and retest.
Suspension setup is iterative — the more you dial it in, the better the bike feels.
Final Thoughts
Setting sag correctly is the single most important step in achieving a balanced, predictable, and high-performing mountain bike setup. It affects traction, geometry, braking, climbing, descending, and overall control. With proper sag, even mid-range suspension feels dramatically better; without it, even the most advanced suspension feels compromised.
Start with recommended numbers, make small adjustments, and focus on balancing the fork and shock together. Once sag is dialed, every aspect of your ride improves — more confidence, more traction, more comfort, and more speed.
FAQ
How important is setting sag on a mountain bike?
Very important. Sag affects geometry, traction, support, and handling. It is the foundation of proper suspension setup.
Do I set sag wearing full riding gear?
Yes. Sag must be measured with your full riding weight, including water, tools, and pack.
Should fork and shock sag be the same?
No. Fork sag ranges 15–20%, while rear shock sag typically runs 25–30%. What matters most is balance, not matching numbers.
How often should I check sag?
Monthly, or anytime your suspension feels “off,” or after service.
Can I set sag without help?
Fork sag — yes. Rear shock sag — almost impossible to do accurately alone.
Why does my sag change over time?
Air suspension loses small amounts of pressure naturally; temperature also affects readings.
Is coil sag set differently from air?
The measurement is the same, but adjustments are done using preload instead of air pressure.
Related Content:
- Full Suspension Setup Guide
- Best Mountain Bike Brands
- Trek vs Specialized
- Santa Cruz Bikes Review
- Yeti Bikes Review
Why Trust This Guide?
BestBikeBrands is built by lifelong cyclists with decades of real-world experience — in the shop, on the trail, and behind the wrench. Our goal is simple: to help riders choose the best bikes and gear with confidence, backed by expert insights and hands-on testing. Learn more about us →
