The fundamentals: pressure and SAG
Before touching any dials, the foundation of any MTB suspension setup is air pressure and SAG.
Air pressure
Pressure determines how firm your suspension is. More pressure means harder. Each manufacturer provides a pressure/weight chart — that's your starting point, not a final value.
Approximate values (25-30% SAG):
| Rider weight (equipped) | Fork (typical) | Shock (typical) |
|---|---|---|
| 60 kg / 132 lb | 55-65 psi | 130-150 psi |
| 70 kg / 154 lb | 65-75 psi | 150-170 psi |
| 80 kg / 176 lb | 75-85 psi | 170-200 psi |
| 90 kg / 198 lb | 85-100 psi | 200-230 psi |
These values are approximations. Each fork and shock has its own specs. Consult the manufacturer's guide.
SAG (static sag)
SAG is the percentage of travel used under the rider's weight at rest. It is THE fundamental setting.
- Trail / All-Mountain: 25-30% of travel
- Enduro: 25-30%
- DH: 28-35%
- XC: 15-25%
Measurement method:
- Push the o-ring against the stanchion or shock body
- Mount the bike in a natural position, feet on pedals
- Settle gently (no bouncing) and stay still
- Dismount WITHOUT compressing the suspension
- Measure the distance the o-ring has traveled
Calculation: SAG (%) = (distance traveled / total travel) × 100
Rebound: the return speed
Rebound controls how fast the suspension returns to its position after compression. It's the red dial (usually) at the bottom of the fork or on the shock.
Rebound too fast: the suspension "bounces" like a ball. The bike is unstable, you lose control in successive hits. The wheel leaves the ground in rapid compressions.
Rebound too slow: the suspension doesn't return fast enough between obstacles ("packing down"). It gradually sinks deeper into the travel and you lose ground clearance. By the end of a descent, you're riding on the end stroke.
Setup method:
- Set rebound to fastest (dial fully open)
- Sit on the bike, push hard on the handlebars/saddle and release
- Slow the rebound click by click until the suspension returns quickly WITHOUT bouncing past its SAG position
Tip: start on the fast side and slow down. It's easier to feel the sweet spot going in this direction.
Compression: low speed vs high speed
Compression controls the resistance of the suspension as it compresses. On high-end suspension, it's split into two circuits:
Low Speed Compression (LSC)
LSC controls slow suspension movements: pedal bob, weight transfer in berms, long progressive compressions.
- More LSC = the suspension resists bob better, the bike rides higher in its travel, more efficient pedaling
- Less LSC = the suspension is softer, absorbs small bumps better, the bike is more comfortable
Typical setting: 3-5 clicks from fully open for trail. More closed for XC (anti-bob), more open for DH (sensitivity).
High Speed Compression (HSC)
HSC controls fast impacts: roots, rocks, jump landings, drops. This is the compression that protects you from big hits.
- More HSC = the suspension uses less travel on big impacts, but transmits more shock to the rider
- Less HSC = the suspension absorbs big hits better, but you risk more frequent bottom-outs
Typical setting: start in the middle and adjust based on feel. If you bottom out frequently → close HSC. If the bike feels harsh on violent impacts → open it.
On a Fox 36/38, HSC is the large blue dial (flat) and LSC is the small blue dial (raised). On a RockShox Lyrik/Zeb, it's the dial at the bottom right of the fork.
Volume spacers / Tokens: progressivity
Volume spacers (Fox) or Bottomless Tokens (RockShox) reduce the air chamber volume. Result: the deeper the suspension compresses, the firmer it becomes. This is the progressivity curve.
No spacers: the suspension is linear. It compresses easily and bottom-outs are frequent.
With spacers: the suspension is progressive. It stays supple at the beginning of the travel but becomes increasingly firm toward the end.
Typical configuration:
| Discipline | Fork spacers | Shock spacers |
|---|---|---|
| XC | 0-1 | 0-1 |
| Trail | 1-2 | 1-2 |
| Enduro | 2-3 | 2-3 |
| DH | 2-4 | 2-3 |
Add spacers if you bottom out regularly despite closed HSC. Remove them if the suspension is too stiff at end-stroke and you never use full travel.
