Academy Suspension Setup

What is Suspension Setup?

Suspension setup is the art of matching your shock and fork settings to your weight, riding style, and terrain. It is where kinematic theory meets trail feel.

A perfectly designed suspension linkage is only as good as its setup. Sag, compression damping, rebound damping, and volume spacers all interact to determine how the bike feels on the trail. Getting these right transforms a bike from okay to dialed — and the process is highly rider-specific.

BikeSPEZL's approach to suspension setup is grounded in data: your body weight and position (from the BDC scan), your gear set, and your bike's kinematic design all feed into the recommended settings. But the final tuning always comes down to trail testing and personal preference.

Sag

Starting point for all tuning

Compression

Controls dive and bob

Rebound

Controls return speed

Volume

Controls end-stroke feel

Sag — The Foundation

Sag is how much the suspension compresses under static rider weight. Everything else builds on this baseline.

Diagram — Measuring sag: O-ring on stanchion at static vs full extension

Sag is measured as a percentage of total travel

Sag is expressed as a percentage of total travel. For rear shocks, typical sag ranges are 25–35%. For forks, 15–25% is common. The sag point determines where the suspension sits in its travel at rest — and therefore which part of the leverage curve, Anti-Squat curve, and Anti-Rise curve the bike operates in during normal riding.

1More sag (30–35%): Plusher, more traction, but may feel less efficient pedalling and bottom out easier.
2Less sag (20–25%): Firmer, more efficient, but harsher on small bumps and less traction in rough conditions.
3Cross-country: typically 20–25% rear sag for pedalling efficiency.
4Enduro/downhill: typically 28–35% rear sag for traction and bump absorption.

🔑 Key Concept

Sag is set by adjusting air pressure (for air shocks) or spring rate (for coil shocks). The goal is to achieve the target sag percentage with the rider in their normal riding position, fully kitted with gear.

Sag % = (static compression / total travel) × 100

Target sag (mm) = total travel (mm) × sag percentage (%)

Compression Damping

Compression damping controls how fast the suspension compresses when hitting an obstacle. It is split into low-speed and high-speed circuits.

Compression damping restricts the flow of oil as the suspension compresses, controlling the speed of compression. Modern shocks and forks have two independently adjustable circuits:

1Low-speed compression (LSC): Controls slow compression movements — weight transfer under braking, pedalling bob, G-out transitions. Affects chassis stability and pedalling efficiency.
2High-speed compression (HSC): Controls fast compression movements — hitting rocks, roots, drops, landings. Affects how the suspension absorbs sharp impacts.
3More LSC: Less dive under braking, firmer pedalling platform, but less traction on smooth terrain.
4More HSC: Resists bottoming on big hits, but may feel harsh on consecutive rapid impacts.

Diagram — Compression damping curve: force vs compression velocity

LSC affects the low-velocity region, HSC affects the high-velocity region

The compression damping curve has a knee where LSC transitions to HSC. Below the knee (slow shaft speeds), LSC dominates. Above the knee (fast shaft speeds), HSC takes over. The position of the knee and the steepness of each region determine the overall feel.

✅ Tip

Start with compression fully open (minimum damping) and add clicks until the bike feels controlled without feeling harsh. It is always easier to add damping than to remove it — start soft and tune up.

Rebound Damping

Rebound damping controls how fast the suspension returns after compressing. Too fast and the bike feels springy; too slow and it packs down.

After the suspension compresses over a bump, the spring or air pressure pushes it back to the sag position. Rebound damping controls the speed of this return. Like compression, it is often split into low-speed and high-speed circuits, though many shocks have a single rebound adjuster.

1Too fast rebound: The suspension kicks back aggressively after compressing. The bike feels bouncy and unstable. Can buck the rider over successive hits.
2Too slow rebound: The suspension does not return fast enough between hits. It packs down — each successive bump compresses it further until it bottoms out. Feels dead and harsh.
3Correct rebound: The suspension returns to sag quickly but smoothly. Tracks the ground through consecutive bumps without packing down or kicking.
4General rule: Faster rebound for smooth terrain, slower rebound for rough, successive impacts.

💡 Insight

The ideal rebound setting depends on the spring rate and the terrain. A stiffer spring (higher air pressure, less sag) needs more rebound damping to control the faster return. Riders often need to adjust rebound when they change sag or air pressure — the two are linked.

Volume Spacers & Progression

Volume spacers change the air spring curve's shape, making the suspension more or less progressive without changing the sag.

Graph — Air spring force vs travel with different volume spacer counts

More spacers = more progressive = firmer at the end of the stroke

Air shocks and forks use volume spacers (tokens) to reduce the air chamber size. A smaller chamber compresses more rapidly — the air pressure rises faster as the suspension goes deeper into travel. This makes the spring curve more progressive: softer at the start, firmer at the end.

1More spacers: More progressive. Softer off-the-top (more small-bump sensitivity), firmer near bottom-out (resists harsh bottoming). Good for light riders or aggressive terrain.
2Fewer spacers: More linear. Consistent feel through the travel. Easier to use full travel. Good for heavier riders or smoother terrain.
3Coil shocks: Progression is determined by the spring rate and the linkage — no volume adjustment. The coil spring is inherently linear.
4The linkage's leverage ratio also affects progression — a falling-rate linkage pairs well with a progressive air spring.

🔑 Key Concept

Volume spacers do not change sag — they change the shape of the spring curve after sag. This makes them a powerful tool for fine-tuning bottom-out resistance without altering the bike's static setup.

The Tuning Process

Suspension tuning is iterative. Start with the basics, test on trail, and adjust one variable at a time.

A systematic approach to suspension setup ensures you do not chase your tail. Change one thing at a time, test on a consistent trail, and take notes. Here is the recommended order:

11. Set sag first — this is your baseline. Adjust air pressure until you hit the target percentage with full riding gear.
22. Set rebound — find the speed that returns to sag without kicking or packing down. Test on a section with successive bumps.
33. Add compression — start fully open, add clicks until dive and bob are controlled without losing bump sensitivity.
44. Add volume spacers — only if you are bottoming out too easily or the end-stroke feels too soft. One spacer at a time.
55. Fine-tune — make small adjustments based on trail feel. Let your hands and feet be the judge.

✅ Tip

In BikeSPEZL's Ride Dynamics module, your sag setting affects D_COG, which in turn affects Anti-Rise, Anti-Squat, and weight distribution. Changing sag is not just about comfort — it changes the entire dynamic behaviour of the bike. Use the simulation to see the cascading effects before you make changes on the trail.

🔑 Key Concept

Suspension setup is never done. Terrain, temperature, fitness, and even tyre pressure all affect the ideal settings. The goal is to understand the system well enough to make informed adjustments — not to find a single perfect setting.