Sag is the foundation of every suspension setup. Not because it's magic, but because it determines where in the travel your suspension works. If the bike sits too high or too low at rest, you'll later only be fighting symptoms with rebound, compression or tokens, not the cause.
In this article I'll show you a method for setting your sag cleanly and repeatably, whether you ride enduro or downhill.
Part 3 of the series MTB-Raceshop Pro Suspension. Previously: Part 1 What your suspension really does · Part 2 Suspension terms explained.
What sag does, in one sentence
Sag is how far your suspension compresses under your static weight with all your kit on. It defines the working range in which your fork and shock respond on the trail.
What incorrect sag does
Too little sag
- The bike sits high.
- It feels harsh and nervous.
- You have little grip over small bumps.
Too much sag
- The bike sits low.
- It feels unstable and wallows.
- There's a lack of support in the mid-stroke.
Before you measure: 5 mistakes that skew every measurement
- Measuring without your full kit. Backpack, shoes, helmet, pads and water quickly add 5 to 8 kg.
- Wrong body position. Standing stiffly or leaning on the bar shifts the sag towards the front.
- Not bouncing first. Without a few bounces, seal friction (stiction) keeps the suspension sitting too high.
- Sloping ground or a brake applied. Both distort the weight distribution.
- Only one attempt. Measure two or three times and take the average.
What's the right sag? Guide values for enduro and downhill
| Use | Fork (front) | Shock (rear) |
|---|---|---|
| Enduro and all-round gravity | 15–20% | 28–32% |
| Downhill, bike park, very rough terrain | 18–22% | 30–35% |
Important: these are starting values, not a law. What matters is the balance between front and rear, how the bike feels and how you use the travel. Also check the specifications from your fork, shock and bike manufacturer: some rear suspension designs are built for a specific sag.
How to calculate sag as a percentage
Sag in % = sag in mm ÷ travel in mm × 100
- Fork: use the fork's travel. Example: 34 mm of sag with 170 mm of travel gives 20%.
- Shock: use the shock's stroke, not the rear wheel travel. The stroke is the second number of the shock size, for example 65 in 230x65. Example: 19.5 mm of sag with 65 mm of stroke gives 30%.
Step by step: setting sag on the fork
You'll need
- a shock pump
- the O-ring on the stanchion (or a cable tie)
- something to take notes with – your phone will do
- ideally a second person to hold the bike
How to do it
- Fully open the fork: open mode, no platform.
- Push the O-ring all the way down against the dust wiper.
- Get on the bike in your riding position: neutral, looking ahead, elbows slightly out, weight centred. Don't hang on the bar.
- Bounce gently two or three times, then stand still.
- Get off without compressing the fork any further.
- Measure the distance from the dust wiper to the O-ring and convert it to a percentage.
- Adjust the air pressure: too little sag means lower the pressure, too much sag means increase it. After each change, cycle the fork a few times so the positive and negative chambers equalise.
- Repeat until you're within the target range. It usually takes two to four rounds.
Step by step: setting sag on the shock
Before you start
- Set the shock to open too, not climb or pedal mode.
- After every pressure change, cycle the shock a few times so the positive and negative chambers equalise. Only then measure.
How to do it
- Push the O-ring against the shock body.
- Get on the bike in a neutral riding position.
- Bounce, then stand still.
- Get off without compressing the shock further.
- Read the sag: directly at the O-ring in mm or on the sag scale, if your shock has one.
- Adjust the pressure and repeat.
Coil shocks
On a coil shock, you set the sag with the spring rate, not with air pressure. Preload isn't meant for this: it only shifts the sag slightly and doesn't change the spring rate. If the sag isn't right, you need a different spring. Work out which one with our spring rate calculator.
The most common mistake: the sag is right, but the bike still feels odd
Then it's usually not the sag that's wrong, but the balance between front and rear:
- Front too high, rear too low: the bike steers sluggishly and the rear feels soft.
- Front too low, rear too high: the bike gets nervous and you feel like you're going over the bar.
“Sag isn't just a number. Sag is a ratio between front and rear.”
Quick check on the trail
After setting up, ride the same section once or twice. The O-ring then shows you how much travel you used.
Travel usage
- Never close to the end: possibly too little sag or too much damping
- Frequent bottom-outs: possibly too much sag, too little progression or too little high-speed compression
Ride feel
- Nervous, kicks: rebound often too fast
- Gets harsher as the run goes on: rebound often too slow (packing)
I'll show you how to set your rebound correctly in the next part of the series.
Mini setup log
So you don't start from scratch every time, note down after setting up:
- Fork air pressure (psi or bar)
- Shock air pressure or spring rate
- Sag front and rear in %
- Rebound clicks, counted from fully closed
- Compression clicks or mode, if available
- Number of tokens
That's the difference between fiddling with dials and getting better systematically.
Frequently asked questions about sag
How much sag do I need on the fork?
As a starting point, 15 to 20% for enduro and 18 to 22% for downhill and bike park. Then fine-tune based on feel and balance.
How much sag do I need on the shock?
As a starting point, 28 to 32% for enduro and 30 to 35% for downhill. It's calculated using the shock's stroke, not the rear wheel travel.
Do I need to measure sag with my backpack on?
Yes. Always measure with the kit you ride in: helmet, shoes, pads, backpack and water.
Can I set the sag on a coil shock with preload?
Only to a small extent. Preload doesn't change the spring rate. If the sag isn't right, you need a different spring.
How often should I check my sag?
After any change to your kit or weight, after a service and at the start of the season. Air springs lose a little pressure over time, so a quick check before your ride is worthwhile.
Want it spot on? In Setup-Coaching we set up your suspension together with you, and with Suspension Fitting we measure with telemetry on your track. And if your suspension still isn't working properly despite the right sag, a service may be due.
Cover image: SRAM / RockShox