Motorcycle Suspension Tuning Guide
Suspension tuning is about controlling how your bike reacts to forces. At its core, you are managing three things: spring force, damping force, and geometry.
Contents
The Three Fundamentals
Spring Force
Supports the weight of the bike and rider. Determines ride height, sag, and how the suspension responds to forces. Get the spring rate right first — everything else depends on it.
Damping Force
Controls how quickly suspension moves. Created by oil flowing through valves and shim stacks. Without damping, the suspension would oscillate uncontrolled after every bump.
Geometry
Head angle, trail, swingarm length, linkage ratio. These determine how forces are distributed between front and rear — and how the bike handles at different speeds.
The Three Main Problems
Most suspension issues fall into one of three categories:
Too Harsh
Suspension resists movement instead of absorbing terrain. Small bumps transmit directly to the rider. Common in forks with stiff initial shim stacks or excessive oil height.
Read: Fork Harsh on Small Bumps →Too Soft / Packing
Suspension can't recover between impacts. The bike sinks into the stroke and traction drops. Usually caused by slow rebound damping.
Read: Shock Packing Down →Poor Control
Suspension feels disconnected or unpredictable. Different parts of the stroke behave differently. Often a compression/rebound imbalance.
Read: HSC vs LSC Explained →Understanding Damping
Damping controls how quickly the suspension moves. It is created by:
Oil flow through valves and shim stacks. When the suspension compresses or extends, oil is forced through ports in the damping piston. Shim stacks covering these ports resist the flow — the more resistance, the more damping force is produced.
The damping force depends on:
- Shaft velocity — faster movement = more oil flow = more force
- Shim stack stiffness — stiffer stack = more resistance to oil flow
- Oil viscosity — heavier oil = more resistance at all velocities
- Port size and number — larger/more ports = less resistance
- Bleed flow — bypass flow that provides low-speed damping control
This relationship between shaft velocity and damping force is described by the force-velocity curve — the most important tool in suspension tuning.
Common Issues and Fixes
- Fork harshness → compression damping too stiff — reduce initial stack stiffness, check oil height
- Packing → rebound damping too slow — speed up rebound, balance compression and rebound
- Bottoming → spring too soft and/or high-speed compression too low — check spring rate first, then stiffen HSC
- Headshake → fork/shock damping imbalance — check that front and rear are tuned as a system
- Arm pump / fatigue → everything too stiff for the terrain — soften compression, especially in forks
The Modern Approach
Old Method
- Guess a shim stack change
- Disassemble, rebuild, reassemble
- Test ride
- Repeat (hope for the best)
Modern Method
- Model the current stack digitally
- See the force-velocity curve
- Predict the effect of changes
- Simulate on track data
- Build with confidence
The old method works — eventually. But it costs time, money, and a lot of unnecessary rides on bad suspension. The modern approach uses data to shortcut the process: model, predict, refine, then build once.
Tools That Change Everything
The Shim Calculator allows you to:
- Predict damping behaviour — enter your shim stack and see the force-velocity curve instantly
- Compare setups — three recommended stacks per circuit (baseline, softer, stiffer)
- Remove guesswork — see the effect of every change before you build
- Simulate on real terrain — validate your stack against 12 track profiles (MX whoops, enduro rocks, road race braking zones)
- Print build sheets — take the recommended stack to the workbench with full specifications
Start Tuning With Data
Enter your shim stacks and see force-velocity curves. Get recommended stacks calibrated to your rider weight, spring rate, and discipline.
Use the Shim CalculatorGo Deeper
The complete methodology is explained in the Suspension Engineer's Handbook — covering shim stack physics, force-velocity theory, tuning workflows, and real-world case studies. Available on the Mountain Race Shop website.
Get the Handbook
The complete suspension tuning methodology — from theory to workshop practice. A$69.95 PDF download.
Buy Now — PDF Download Learn MoreDeep-Dive Articles
Fork Harsh on Small Bumps
Causes and fixes for small bump harshness — what's really going on in the early stroke.
Shock Packing Down
Why the shock can't recover between bumps and how rebound shim stack design fixes it.
HSC vs LSC Explained
High-speed and low-speed compression refer to shaft velocity, not bike speed. Here's what that means.
How to Build a Shim Stack
Stack structure, key principles, and the cube relationship between thickness and stiffness.
Beginner's Revalving Guide
Complete guide to motorcycle suspension revalving — tools, process, and common mistakes.
Compare Suspension Tools
ShimCalculator vs ReStackor vs Motoklik — feature-by-feature comparison.