Your suspension is the single biggest factor in how your bike rides. Get the basics right and everything else — cornering, braking, jumping, traction — gets easier. This guide covers the settings riders search for most, in the order you should set them.
1. Start with sag
Sag is how far the suspension compresses under your static body weight, expressed as a percentage of total travel. It sets your ride height and where the suspension sits in its stroke at rest.
- Front fork: 15–20% sag
- Rear shock: 25–30% sag (up to 33% for plusher enduro setups)
Too little sag and the wheel can't drop into holes for traction; too much and you've already used travel before you hit anything. Sag is the foundation — everything else is tuned relative to it.
How to measure it: Stand on the bike in your full riding kit, level ground, against a wall for balance. Compress the suspension a few times to settle it, then let it rest at equilibrium. Measure the exposed stanchion (fork) or use the O-ring on the shock shaft, against your total travel. Divide compressed travel by total travel × 100 = sag %.
2. Air pressure: the chart is a starting point, not the answer
Every air fork and shock ships with a pressure chart. It takes your weight, points at a number, and says "put this much air in." That chart is not wrong — it's incomplete. It can't account for your riding style, terrain, kit weight, or temperature.
- Start with the manufacturer's chart for your weight.
- Adjust pressure until you hit your sag target (above).
- Fine-tune from there based on how the bike rides.
A 75 kg trail rider might land around 70–85 psi in a typical fork, but the correct number depends on your fork model, travel, and style. Use sag percentage as your guide, not a fixed pressure number.
Tip: Set your pressure at the trailhead, not in a warm garage. Air pressure changes with temperature — a 15°C difference can shift pressures 3–5 psi.
3. Rebound: how fast the suspension returns
Rebound damping controls how quickly the suspension extends after compressing. Too fast and the bike feels springy and uncontrolled; too slow and the suspension "packs down" — it doesn't recover between successive hits, riding deeper and deeper into its travel.
- LSR (low-speed rebound): controls slow, deep movements — the return after braking dives, G-outs, and jump landings.
- HSR (high-speed rebound): controls fast, sharp returns — the kick after a square-edge hit or drop landing.
The drop test: Stand next to the bike, push down hard on the saddle, and release. The bike should return to its resting position once, without bouncing past it or lagging behind. This tells you if rebound is wildly wrong — it does not tell you how it behaves through 50 consecutive impacts at speed. Validate on the trail: if the bike packs down on rough descents, speed the rebound up regardless of how it felt in the car park.
Match sag percentages between front and rear, not rebound click positions. The fork typically needs faster rebound than the shock.
4. Compression: less is usually more
Compression damping controls how the suspension resists being pushed down. Too much and the fork stops reacting to small bumps — the very impacts you bought suspension to absorb. The bike feels rigid and deflective.
- LSC (low-speed compression): pedal bob, brake dive, body-weight movements.
- HSC (high-speed compression): big hits, square-edge impacts, landing forces.
Rule of thumb: start with both fully open (minimum damping). Ride your normal trails. Only add compression if you have a specific reason — excessive dive, bob, or harshness on big hits. Most trail riders need far less compression than they run.
5. Volume spacers: shape the spring curve
Volume spacers (also called tokens) are plastic inserts that reduce the air chamber size, making the spring rate more progressive — softer at the top of the stroke for small-bump sensitivity, firmer at the bottom to resist harsh bottoming.
Add a spacer when:
- You're using full travel on hard rides but the bike feels good everywhere else.
- You want more pop and support without adding air pressure (which would ruin the start of the stroke).
Remove a spacer when:
- The fork or shock feels harsh in the last third of its travel.
- You can't access full travel even on your biggest hits.
- The suspension feels dead and unsupportive when compressed deeply.
Most trail riders benefit from one or two spacers in the fork; the rear shock often runs well stock. Heavier riders (90+ kg) or aggressive terrain may warrant an extra spacer in both.
6. Diagnosing bottom-out
Bottoming out is a symptom with several causes — don't just add air pressure, which fixes the bottom but ruins the rest of the stroke. Work through the causes in order:
- Too much sag → add air pressure to hit your sag target.
- Not enough volume spacers → add a spacer for end-of-stroke support.
- Not enough compression damping → add HSC to resist big-hit forces.
Diagnose the cause first, then apply the matching fix.
7. The most common mistakes
- Running too much pressure. The #1 mistake. Feels fast on smooth ground, harsh and skittish on rough. If you're not using 70–80% of fork travel on a real ride, there's too much air in it.
- Setting up in the garage, not at the trail. Temperature shifts move your pressure. Bring the shock pump.
- Ignoring kit weight. A 3 kg pack changes your correct shock pressure by 5–10 psi. Set up wearing what you ride with.
- Setting rebound by feel in the car park. Use the drop test, then validate on trail.
- Matching fork and shock rebound exactly. Match sag %, not click positions.
- Adding air to fix bottoming. Diagnose the cause first (see above).
- Never re-checking. Air seals leak, temperatures change, your weight and riding evolve. A monthly pressure check keeps your setup honest.
8. When to re-check your setup
- Start of every ride season
- After a temperature swing of more than 10°C
- When riding at altitude
- After any fork or shock service
- Monthly, because air forks and shocks lose small amounts over time
How Trail Tuner helps
Trail Tuner turns this methodical process into a guided workflow, so you start from a balanced, model-specific setup instead of guessing from a generic chart:
- Set Up generates a model-specific baseline — sag, air pressure, compression, rebound and tire pressure — from your weight, riding style and exact fork/shock models.
- Tuner AI takes a handling complaint ("the front pushes in corners", "shock packs down on rock gardens") and returns model-specific adjustment recommendations for your exact hardware.
- History logs every change you make with the reason, so you can roll back to a setup that worked and never lose a good baseline.
- Compare puts two setups side by side to see exactly what changed between them.
- Charts visualise how your settings have moved over time, so trends and drift are obvious at a glance.
Suspension setup isn't complicated — it's methodical. Set sag, tune pressure, dial rebound, add compression only when needed, and use spacers to shape the end of the stroke. The difference between a bike you tolerate and a bike you trust lives in those twenty minutes.