MTB Compression Calculator

Starting points for LSC and HSC compression damping. Based on Fox and RockShox setup manuals.

LSC
7
clicks from closed
range: 5–9
Low Speed Compression
HSC
4
clicks from closed
range: 2–6
High Speed Compression
Turn OUT (counterclockwise) to open compression (more supple) · Turn IN (clockwise) to add damping (firmer)
⚠ For reference only. Compression tuning is the most complex part of suspension setup. These are baseline starting points — many riders find factory (mid-range) settings work well until they develop a feel for their suspension's behaviour.

Sources: Fox Owner's Manuals and RockShox Suspension Setup Guide

How it works

Compression Damping — Resisting Compression

Compression damping resists the suspension compressing. LSC (Low Speed Compression) affects small, slow inputs — pedalling forces, braking dive, rolling compressions. HSC (High Speed Compression) affects fast, large inputs — drops, square-edged hits, high-speed compressions. They are adjusted separately on mid-range and high-end suspension.

Clicks are counted from fully closed (maximum compression damping). Turning OUT (counterclockwise) opens the compression circuit for a more supple feel.

Frequently asked questions

What is the difference between LSC and HSC?

LSC (Low Speed Compression) controls damping for slow suspension movements — braking, pedalling forces, and gradual compressions. HSC (High Speed Compression) controls fast impacts — square-edged rocks, drops, and high-speed hits. They affect different shaft speeds in the damper, not riding speed.

Should I start with more or less compression?

Start with the manufacturer's mid-range setting and adjust from there. Most Fox and RockShox forks leave the factory close to mid-range compression. Adding too much compression makes the ride harsh; too little causes excessive dive and poor small-bump sensitivity.

My fork dives a lot under braking — which adjuster?

Braking dive is a low-speed movement, so increase LSC (turn clockwise, add damping) by 2 clicks. If dive is still excessive after 4 clicks, also check that sag is set correctly — too much sag increases braking dive.

My fork feels harsh over small roots and pebbles — fix?

Reduce LSC by 2 clicks (counterclockwise). Small-bump sensitivity is primarily controlled by LSC and negative spring volume. If reducing LSC makes the fork dive too much under braking, you may need a volume spacer removed or a different damper tune.

What is platform/pedalling mode?

Many trail and enduro forks and shocks offer a platform mode (ProPedal on RockShox, Trail mode on Fox) which adds LSC specifically to reduce bobbing while pedalling. This is separate from the main LSC adjuster. Use platform mode while climbing, open it for descents.

Does compression affect sag?

No — compression damping does not affect the static sag. Sag is determined by air spring pressure alone. You can change compression damping without affecting sag or rebound settings.

What is the correct setup order?

Always set up in this order: 1) Sag (air pressure first). 2) Rebound. 3) LSC. 4) HSC. Setting sag first ensures the spring rate is correct before tuning damping. Tuning compression before sag is set correctly wastes time as you will need to readjust.

My shock has only one compression adjuster — which is it?

Budget and mid-range shocks (RockShox Select, Fox Float Performance) typically have a single compression adjuster that blends LSC and HSC. Use the LSC value from this calculator as your starting point. Dedicated LSC and HSC adjusters appear on Shimano, Fox Factory, and RockShox Ultimate level components.