SAG setup: the foundation of your suspension

What is SAG?

SAG is the amount your suspension compresses under the rider's weight in a static position. In simple terms: how much your fork or rear shock sinks when you get on the bike without moving.

It is adjustment number one. If SAG is wrong, no other adjustment (rebound, compression, tokens) can compensate. You always start here.

Why does it matter?

Suspension must work in both directions: compression (absorbing an obstacle) and extension (following dips). If SAG is too low (suspension too firm), the wheel lifts off in dips and you lose traction. If SAG is too high (suspension too soft), you use too much travel and bottom out on big hits.

How to measure SAG

O-ring method

Most forks and shocks have an O-ring (small rubber ring) on the stanchion:

1. Fully deflate the fork, then re-inflate to your starting pressure (start with your weight in kg = pressure in PSI as a baseline)
2. Fully open rebound and compression (turn dials all the way counter-clockwise)
3. Push the O-ring up against the dust wiper (top of the stanchion)
4. Get on the bike in full riding gear (helmet, pack, water bottle). Have someone hold you or lean against a wall
5. Settle into your natural riding position (not standing on the pedals, not sitting like on a road bike — your normal ride position)
6. Dismount gently without bouncing the suspension
7. Measure the distance between the O-ring and the dust wiper. That is your SAG in millimetres

Calculating the percentage

SAG (%) = (static compression / total travel) x 100

Example: your fork has 150 mm of travel. The O-ring shows 40 mm of compression. SAG = 40/150 = 26.7%.

Target values by discipline

These values are starting points. The goal is to use the full travel during a ride without bottoming out. If you bottom out often, add pressure. If you only use 80% of travel, remove pressure.

Adjusting air pressure

• Too much SAG (suspension too soft) → add air (5 PSI at a time)
• Not enough SAG (suspension too firm) → remove air (5 PSI at a time)
• High-pressure pump required (suspension-specific pump, not a tyre pump)
• Note: when you disconnect the pump, you lose approximately 5-10 PSI. Account for this

Tokens and volume spacers

Tokens (Fox) or volume spacers (RockShox) reduce the air volume in the positive chamber. The effect: the suspension becomes more progressive (the more it compresses, the firmer it gets). This does NOT change SAG, but it prevents bottoming out.

• More tokens = more progressive suspension, firmer at end of stroke → for aggressive riders or long-travel setups
• Fewer tokens = more linear suspension, more comfortable → for lighter riders or XC

Next adjustments: rebound and compression

Once SAG is correct:

Rebound: controls how fast the suspension returns to full extension. Too fast = the bike bounces like a kangaroo. Too slow = the suspension "packs down" (it does not recover fast enough between successive hits). Rule of thumb: drop your weight onto the bike; the fork should return quickly but without launching you.

Low-speed compression (LSC): controls sag under slow movements (braking, cornering, pedalling). The more you close it, the less the suspension bobs while pedalling.

High-speed compression (HSC): controls compression on fast impacts (roots, rocks). Most trail forks do not have this adjustment — it is reserved for high-end forks.

Want to know the recommended pressure range for your weight on your exact fork model? L'Atelier finds those specs in the manufacturer's technical documentation.