High-Speed vs Low-Speed Compression — What They Actually Mean
This is one of the most misunderstood concepts in suspension tuning.
"High-speed" and "low-speed" do NOT refer to bike speed.
They refer to shaft velocity — how fast the damper rod is moving inside the fork or shock body. A rock hit at walking pace can produce high-speed compression. Smooth weight transfer at 200 km/h is low-speed compression.
Low-Speed Compression
Low-speed compression damping controls how the suspension responds to slow shaft movements:
- Chassis movement — weight transfer under acceleration, braking, cornering
- Braking dive — how much the fork drops under braking force
- Cornering stability — resisting squat and dive through direction changes
Examples of low-speed compression events:
- Rolling weight transfer
- Smooth braking inputs
- Gradual terrain changes
- Rider body position shifts
High-Speed Compression
High-speed compression damping controls how the suspension responds to fast shaft movements:
- Sharp impacts — rocks, roots, square-edge bumps
- Landing forces — jumps, drops, whoops
- Braking bumps — rapid successive impacts
Why This Matters
Bike feels soft in corners but harsh on bumps
Low-speed compression is too soft, high-speed compression is too stiff.
- Fix: increase LSC, decrease HSC
- Shim stack: stiffer initial engagement, softer at full deflection
Bike feels stable but uncomfortable
Low-speed compression is correct, high-speed compression is too stiff.
- Fix: decrease HSC only
- Shim stack: reduce clamping force on outer shims
Bike dives under braking but absorbs bumps well
Low-speed compression is too soft, high-speed compression is good.
- Fix: increase LSC only
- Shim stack: stiffer face shim or reduce bleed
Bike bottoms on big hits
High-speed compression and/or spring rate too soft.
- Fix: check spring rate first, then increase HSC
- Shim stack: more support shims or larger outer diameter
Where Shim Stacks Come In
Low-speed damping
Controlled by bleed flow + early shim stack movement. At low shaft velocities, oil flows primarily through bleed holes and the initial gap as the first shim lifts off the seat. The face shim diameter and bleed specification dominate.
High-speed damping
Controlled by full shim deflection + port flow. At higher shaft velocities, the entire stack deflects and oil flows through the main ports. The number, diameter, and thickness of the backing shims dominate.
The Problem
Most riders adjust clickers without understanding which part of the damping curve they are changing.
Compression clickers primarily affect low-speed damping. If your problem is high-speed harshness (rocks, roots, braking bumps), no amount of clicker adjustment will fix it — you need to change the shim stack.
The Solution
The Shim Calculator lets you:
- Visualise the complete damping curve — force vs shaft velocity
- See exactly where low-speed ends and high-speed begins for your stack
- Tune each zone independently by modifying specific parts of the stack
- Compare before and after — see the effect of each change on the curve
See Your Damping Curve
Enter your shim stacks and see the complete force-velocity curve. Identify which zone needs adjustment.
Use the Shim CalculatorGet the Handbook
The Suspension Engineer's Handbook explains the complete theory behind low-speed and high-speed damping — from fluid dynamics through shim stack mechanics to practical tuning workflows. A$69.95 PDF download.
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