Summary

Suspension sag adjustment is the process of setting how much a bicycle’s suspension compresses under the rider’s body weight—gear included—while stationary. This setup step is essential to making the suspension system work effectively within its intended travel range. When dialed in properly, sag enhances traction, improves rider comfort, and allows the bike to maintain control and composure over varied terrain. It’s a foundational principle in modern mountain bike performance—and one that’s often overlooked.

Key Facts

Introduced: Common in MTB setup practices since the 1990s
Category: Concepts
Also Known As: Sag Setting, Rider Sag, Static Sag
Used By / Found On: Mountain bikes, full-suspension e-bikes, select gravel bikes with front suspension
Official Website: Not applicable (standardized setup principle, not brand-specific)

Overview

Suspension sag refers to how much a bike’s suspension compresses under a rider’s static body weight—before the bike even starts moving. It’s measured with the rider sitting in a neutral position, fully geared up, with no external forces like pedaling or bumps involved. Sag acts as a “starting point” for how suspension behaves and how much travel remains to absorb terrain both upwards and downwards.

In practice, sag determines how the bike sits in its travel, how it responds to terrain changes, and how well it maintains traction. Too little sag, and the ride feels harsh and nervous; too much, and the suspension bottoms out, pedals strike, or the geometry shifts out of optimal range.

Sag is influenced by rider weight, suspension type (air or coil), and even what’s in your hydration pack. Because of this, it must be set individually for each rider and each bike. Whether you’re riding cross-country, trail, enduro, or an e-MTB, getting sag right is the first step in making the bike ride like it’s supposed to.

How It Works

When a rider mounts the bike, their weight naturally compresses the suspension. Setting the correct amount of this initial compression—sag—ensures the suspension stays responsive in both directions. A properly sagged suspension can drop into holes, absorb big hits, and maintain tire contact with the ground, all without overreaching its limits too soon.

1. How Sag is Measured

Sag is typically measured in two ways:

As a percentage of total travel (e.g., 25% of 150 mm = 37.5 mm)
As an absolute distance (e.g., 18 mm of stanchion compression)

To measure sag:

Push the suspension’s O-ring or place a zip-tie against the dust wiper.
Mount the bike wearing your full riding kit and assume a neutral riding position—seated or standing, depending on the bike’s discipline.
Carefully dismount without rebounding the suspension.
Check how far the O-ring moved.
Adjust spring rate (air pressure or coil preload) accordingly.

Front and rear sag are adjusted separately, and rear shock sag may need to factor in the bike’s suspension kinematics—such as linkage progression or anti-squat behavior.

2. Air vs. Coil Springs

Different suspension types handle sag adjustments in distinct ways:

Air Springs
- Adjusted via air pressure using a shock pump.
- Most air shocks and forks include pressure guides based on rider weight.
- Easy to fine-tune, ideal for changing rider loads or trail conditions.
Coil Springs
- Sag is controlled by spring rate (e.g., 450 lbs/in vs. 500 lbs/in) and fine-tuned using threaded preload collars.
- Requires physically swapping coils to change spring rate.
- Offers consistent damping and predictable behavior, but less flexible for tuning.

Air systems dominate most bikes due to their adjustability, while coil shocks are favored in some downhill or aggressive trail bikes for their supple feel.

3. Typical Sag Guidelines by Discipline

Riding Style	Front Sag (%)	Rear Sag (%)
XC Racing	15–20%	20–25%
Trail / All-Mountain	20–25%	25–30%
Enduro / Downhill	25–30%	30–35%
Gravel (suspended)	15–20%	N/A or 20%

Some modern suspension systems feature adjustable modes—climb, trail, descend—each with different sag profiles, activated through lockouts or electronic damping controls.

4. Static vs. Dynamic Sag

Static Sag is measured while the rider is stationary. It’s the traditional benchmark used for setup.
Dynamic Sag refers to real-time compression while riding. This is affected by terrain, rider input, and bike speed.

Professional riders and teams often use telemetry systems, data loggers, or GPS-enabled apps to optimize dynamic sag—especially in racing where terrain-specific fine-tuning can mean the difference between a podium and a crash.

Tuning & Ride Effects

Suspension sag directly influences the way a bike rides. Too much or too little sag throws off balance, cornering dynamics, and even climbing efficiency.

Symptoms of Incorrect Sag

Too Little Sag:

Harsh, chattery ride
Poor small-bump sensitivity
Front wheel feels twitchy or skips in corners
Suspension can “pack down” on repeated hits

Too Much Sag:

Excessive bottoming on jumps or drops
Pedal strikes or low bottom bracket height
Rearward weight bias leads to sluggish steering
Suspension feels “wallowy” or vague in technical sections

Proper sag also ensures front-rear suspension balance. An overly stiff fork combined with a soft rear shock can cause understeer or compromise climbing efficiency. Likewise, too much front sag can steepen head angles and make descents feel nervous.

Many riders start with sag setup, then move on to adjusting rebound damping, compression, or volume spacers to fine-tune behavior.

Notable Use Cases

Downhill Racing

Precise sag tuning is critical to ensure full suspension travel is used without bottoming out too easily. Racers adjust sag based on course features like high-speed chatter or big drops, often revisiting sag multiple times over a race weekend.

Trail Bikes with Dynamic Geometry

Bikes like the Specialized Stumpjumper or Trek Fuel EX rely on sag to engage kinematic features like leverage progression or anti-squat. A few millimeters off, and the bike won’t perform as designed under load.

E-Mountain Bikes

E-MTBs often carry more weight due to motors and batteries. This added mass can cause excess sag if not adjusted. Riders often run lower sag percentages or stiffer spring setups to keep geometry and handling sharp despite the bulk.

Bike Shops & Setup Services

Professional bike shops increasingly offer sag setup services, using digital shock pumps, mobile apps (like ShockWiz), and in-depth rider interviews. These services help riders tailor suspension feel based on skill level, terrain, and preferences—especially helpful for newcomers or riders struggling to find the right balance.

Related Terms

Spring Rate
Rebound Damping
Anti-Squat
Suspension Kinematics
Travel

References

TrailHead App by SRAM

RockShox Suspension Setup Manuals

Fox Racing Shox Tuning Guides

BikeRadar Suspension Setup Fundamentals

Park Tool: Suspension Sag Setup Article

Vorsprung Suspension Tuning Glossary

Suspension Sag Adjustment