MTB SUSPENSION SETUP GUIDE: FORK AND REAR SHOCK, STEP BY STEP

MTB suspension setup is not one rider-weight formula. The transferable part is the sequence: identify the hardware, use the exact source, calculate a measurable sag target, establish spring support, and only then tune damping.

That distinction matters because two products with the same brand name can use different air springs, limits and pressure charts. The same rear shock can also need a different final pressure on different frames. Roadman's MTB suspension calculator now shows a numeric pressure only when a selected current source supports it; otherwise it calculates sag and routes to the official lookup.

Which Roadman page should you use?

1. Identify the exact suspension

Before adding air, record:

• bicycle make, model, size and model year;
• fork make, model, generation, travel and air-spring variant;
• rear-shock make, model, generation, stroke and OEM tune or ID code;
• whether each spring is air or coil;
• every maximum pressure and permitted spacer configuration;
• the official bicycle and component setup links.

Model name alone is not always enough. The 2026 FOX 38 manual, for example, publishes separate starting columns for FLOAT, FLOAT E-Bike+, Rhythm and Rhythm E-Optimized. RockShox sends riders to the fork decal or Trailhead for product-specific pressure and rebound.

For a rear shock, begin with the bicycle manual. Frame leverage and OEM tuning make the bicycle manufacturer's starting point more specific than a generic shock table.

2. Calculate sag in millimetres

Sag is suspension movement under the dressed rider in the normal riding position. The calculation is simple:

Use shock stroke, not rear-wheel travel. A 170 mm fork at 20% sag has a 34 mm target. A 55 mm shock at 30% has a 16.5 mm target.

The percentage must come from the exact source. FOX specifies 15–20% for the selected 2026 38, 25–30% for current FLOAT X/SL and approximately 30% for the 2026 FLOAT X2. Those figures do not prove that every fork, shock or bicycle should use the same target.

3. Establish the starting pressure

Use this order:

1. Bicycle manufacturer's setup guide or supplied setup card.
2. Exact component manual, serial/ID lookup or pressure decal.
3. A calculator only when it identifies and cites that exact method.

FOX's current FLOAT X/SL instructions and FLOAT X2 instructions say to begin with PSI matching body weight in pounds, then equalise and adjust to sag. That is a product-specific first inflation point—not proof that every rear shock on every frame should finish there.

There is no defensible equivalent such as “fork PSI is 60% of body weight”. Use the fork's own chart or lookup. Roadman does not extrapolate a published chart beyond its rider-weight range.

Never exceed the lowest limit that applies to the component and bicycle. If a starting rule would exceed a stated maximum, stop and contact the manufacturers; do not silently cap the number and ride it.

4. Inflate and equalise the air spring

Set compression damping to the open position before measuring sag. Use a high-pressure suspension pump—not a floor pump—and follow the product's exact fill/equalisation sequence.

Equalisation differs. FOX instructs riders to cycle selected rear shocks through part of their travel as pressure is added. Current RockShox DebonAir+ instructions specify staged inflation and slow compressions. Treat those steps as part of the measurement, not optional ritual: the pump reading can change as positive and negative chambers equalise.

Do not deliberately overfill to “allow for air lost when disconnecting”. A pump hose can contain pressurised air when reconnected, and the valve/pump design determines what the gauge shows. Inflate, disconnect and remeasure sag according to the product instructions.

5. Measure sag without adding noise

1. Open the required damping controls.
2. Slide the O-ring to the wiper or air-sleeve seal.
3. Put on helmet, shoes, pads, pack, water and normal carried tools.
4. Use a wall or helper and settle into the position specified by the bike or component maker.
5. Hold still long enough for the suspension to settle.
6. Move the O-ring to the seal if the procedure requires it while weighted.
7. Dismount without bouncing.
8. Measure O-ring movement and compare it with the millimetre target.

If sag is greater than the target, add a small amount of air. If it is smaller, release a small amount. Equalise again where required and repeat. A fixed 5 or 10 PSI step is not equally small across every fork and rear shock.

6. Set rebound from the exact reference

Rebound controls extension speed after compression. Too little damping can let the suspension return abruptly; too much can prevent it recovering between successive hits. That general principle transfers. The click number does not.

Some manuals count clicks out from fully closed, while a product may use another reference. Air pressure can also change the recommended rebound position. Start from the exact product table or Trailhead result, record the reference direction, then test one click at a time on a repeatable trail section.

Do not try to make fork and shock click counts match. They use different dampers, spring forces and adjustment ranges.

7. Set compression after spring and rebound

Compression damping controls resistance while the suspension compresses. The available controls may include a simple open/firm lever, low-speed compression, high-speed compression or none at all.

Begin at the manufacturer's starting position. If support or impact control is wrong, change one applicable control by one step and repeat the same trail. Do not use a generic “two clicks for enduro” rule: the meaning of two clicks depends on the damper.

8. Use volume spacers only inside the product boundary

FOX describes air-volume spacers as a way to change mid-stroke and bottom-out resistance. RockShox describes tokens as reducing air volume and increasing spring progression. Both require the exact product's compatibility and maximum configuration.

Consider an approved spacer change only after sag is correct and the end-stroke behaviour remains inappropriate for representative riding. After a change, repeat sag and damping setup. Do not apply Roadman's old automatic PSI multiplier.

Coil shocks need a different process. Spring rate cannot be selected from rider weight alone; use a bike-specific spring calculator that includes frame motion, travel, stroke and permitted preload.

9. Balance the bike with observations, not slogans

Balanced suspension means the bike responds predictably to the rider and terrain. It does not require equal sag percentages, equal PSI, equal click counts or both ends reaching bottom-out together.

Use a repeatable section with braking, support loads and successive impacts. Record:

One change per run makes the result interpretable.

Stop and get mechanical help when

Do not keep tuning around a fault. Stop riding and use a qualified suspension technician or manufacturer support if:

• the product cannot be identified or its limits are unknown;
• a starting method exceeds a stated maximum;
• the shock is stuck down or will not extend normally;
• pressure drops unexpectedly, oil leaks or exterior damage is visible;
• a control has no effect or the suspension tops out harshly;
• correct sag cannot be reached within the permitted range;
• a spacer or internal change is outside your training and the official procedure.

The right next step for those cases is inspection, not a more aggressive number.

Use the MTB suspension calculator to turn the exact target into millimetres and record the source boundary. Then use the MTB tyre-pressure guide, dropper setup guide and MTB maintenance guide for the other setup jobs.