Suspension has one job: let the wheels follow the ground instead of bouncing off it. The most useful first step is setting sag, the amount the suspension compresses under your weight. FOX’s starting point is 25% of available travel for a fork or rear shock, and you then adjust a few points either way for your riding style. Rebound and compression come after that.
Hardtail or full suspension
- Hardtail: a suspension fork at the front and a rigid rear end. It is simpler and has less to maintain.
- Full suspension: a fork plus a rear shock. It keeps the rear wheel in contact on rough ground, but it has twice as many components to set up and service.
If you are still choosing a bike, see Road Bike, Hybrid or Mountain Bike: Which Should a Beginner Buy? and Getting Started with Mountain Biking.
The three adjustments
- Sag (spring setting): how far the suspension sits into its travel when you are on the bike. On an air fork or shock you change it by changing air pressure. More pressure means less sag.
- Rebound: how fast the suspension extends after being compressed.
- Compression: how firmly the suspension resists being pushed into its travel.
Step 1: Set sag
What number to aim for
Manufacturers and bike makers do not give one universal figure. FOX says to start at 25% for a fork or rear shock and to move a few points depending on style: more sag (less air) for a downhill or shuttle style, less sag (more air) for all-mountain or cross-country riding. ROSE Bikes gives ranges by use.
| Source | Component | Sag target |
|---|---|---|
| FOX | Fork or rear shock, starting point | 25% of available travel |
| ROSE Bikes | Fork | 20-30% of overall travel |
| ROSE Bikes | Rear shock, race / marathon | 15-25% |
| ROSE Bikes | Rear shock, all-mountain / enduro | 20-30% |
| ROSE Bikes | Rear shock, downhill | 30-40% |
ROSE adds that the more travel a bike has, the softer it is set. FOX recommends the same sag percentage on the fork and the rear shock of a full-suspension bike. Your frame maker’s recommendation for your specific bike and shock takes priority over these generic figures.
How to measure it
- Set the pressure the manufacturer recommends for your weight as a starting point (printed on the fork leg or in the manual). Turn off any lockout, pedal platform or compression damping so it does not stop the suspension compressing.
- Put on your normal riding gear, including a filled hydration pack if you use one. Use a wall or a helper to hold yourself up and hold only one brake while you bounce lightly to free up friction.
- Settle into your riding position for 15-30 seconds. FOX specifies a normal seated position for XC, trail and all-mountain bikes and a standing position for freeride and downhill bikes.
- Slide the rubber O-ring (or a zip tie if there is none) down the stanchion or shock body until it touches the seal, then step off without bouncing so it does not move.
- Measure from the seal to the O-ring and divide by the total travel. For example, 25% of a 50 mm shock stroke is 12.5 mm.
- Adjust air in small steps (FOX’s example is 5 psi, or 0.35 bar) and repeat until you reach your target.
Step 2: Set rebound
Rebound damping controls how quickly the fork or shock returns after a hit. Too little and the bike springs back and bounces; too much and it cannot recover between bumps, so the later bumps in a series feel harsh. FOX lists both symptoms:
- Too much rebound damping: the suspension takes the first bump well, then feels harsh over later bumps and has poor traction in washboard corners.
- Too little rebound damping: the front end springs back too quickly after bumps and traction in bumpy corners is poor.
ROSE Bikes gives two quick tests. For the fork, push down on the bars and let go; if the front wheel leaves the ground, slow the rebound. For the rear, roll slowly down the side of a curb: the shock should compress once and then settle, about 1.5 bounces. If the rear end bounces harshly, slow the rebound.
Most rebound dials click in steps. Change one or two clicks at a time and test on the same short piece of trail, and use the maker’s recommended setting for your weight as the baseline.
Step 3: Set compression
Compression damping resists the suspension being pushed in. A firm setting helps on smooth trails and climbs because the suspension moves less; a more open setting lets the suspension work over rough ground. Use FOX’s symptom guide to tell compression problems from spring (air pressure) problems:
| What you feel | FOX’s listed cause | FOX’s listed fix |
|---|---|---|
| Bottoms out, soft throughout the travel | Spring rate too low, or too little compression damping | More air pressure or stiffer spring; more compression damping |
| Harsh over large bumps, fine over small ones | Compression damping too high | Reduce compression damping |
| Harsh over small bumps but uses full travel | Spring rate or preload too high, or too much compression damping | Lower air pressure; reduce compression damping |
Change one setting at a time, and fix sag first. If the fork feels wrong after you have set sag, check the rebound before touching anything else.
Using a shock pump safely
- Use a pump built for suspension, not a floor pump. FOX warns not to cycle the fork or shock with its pump attached, because that can damage the pump.
- Do not exceed the pressure range printed on your fork or shock. FOX’s manual for its air shocks gives a range of 50 to 300 psi for the main chamber and says not to exceed 300 psi. Your component’s own limit is what counts.
- Expect a small pressure drop when the pump connects: FOX says filling the hose can lower the reading by as much as 10 to 20 psi on a shock.
- If a fork or shock will not hold pressure, take it to a service center rather than riding it.
Care and service
Dirt that dries on the stanchion or shock body chafes the wiper seal and lets grit inside. FOX recommends cleaning the exterior after every ride with mild soapy water, not spraying water directly at the seal/upper-tube junction and never using a high-pressure washer. For service, follow the interval for your exact model: brands and model years differ, and FOX’s table uses 30-hour and 100-hour columns for different jobs. FOX adds that frequent riding in extreme conditions (wet and muddy, downhill racing, winter riding) calls for more frequent service.
Lower-leg oil changes are routine shop work, but damper and air-spring servicing is not a beginner job; FOX says suspension fluid service on its rear shocks must be done by FOX or an authorized service center.
When to stop riding and get it inspected
FOX tells owners to inspect the fork for scratches or dents on the upper tubes, damage, deformation or cracks on the crowns, and damage around the brace, disc brake mounts and thru-axle dropouts, including cracks or flaking paint that may indicate structural damage. If you find any of these, stop riding the fork and have an authorized service center inspect it. The same applies to a fork that leaks oil, a shock that loses pressure, or any knocking or play you did not have before.
For related setup, read Tire Pressure: The Most Overlooked Performance Factor in Cycling, the other pressure that shapes how a bike feels on rough ground.
Sources
- FOX: Achieving Correct Air Pressure with Sag
- FOX: Measuring & Setting Sag
- FOX: Suspension Tuning Tips
- FOX: Using the FOX High Pressure Pump
- FOX: Service Intervals
- FOX: Structural Inspection
- ROSE Bikes: Setting up the fork and shock
Last reviewed: October 2026.