What is Pedal Kickback?
When the rear suspension compresses, the rear axle moves along an arc defined by the linkage. This changes the distance from the chainring to the cassette — and the chain pulls the cranks backward.
Pedal kickback is the angular rotation of the crankset that occurs when the rear suspension compresses through its travel. As the rear wheel moves upward along the linkage's arc path, the distance between the bottom bracket (chainring) and the rear axle (cassette) changes. If the distance increases, the chain is pulled taut, which rotates the cranks backward — a kick that the rider feels through the pedals.
Pedal kickback is a direct consequence of chain growth in the suspension design. It is closely related to Anti-Squat: designs with high Anti-Squat typically have more chain growth and therefore more pedal kickback.
What Causes Pedal Kickback?
The rear axle doesn't move straight up and down — it follows an arc. That arc changes the BB-to-axle distance, pulling or feeding chain.
When the suspension compresses, the rear axle follows a path determined by the linkage geometry (pivot positions, link lengths, instant centre). If this path moves the axle away from the BB, the chain must grow longer to accommodate — this is called chain growth. Since the chain is a fixed length (with the derailleur taking up slack), chain growth pulls the chain backward through the cassette, rotating the cranks.
- 1Rear axle moves away from BB → chain growth → pedal kickback
- 2Rear axle moves toward BB → chain feeds → no kickback (rare)
- 3The amount of growth depends on the linkage arc and pivot positions
- 4Derailleur capacity limits how much slack it can take up — excess growth = kickback
How Pedal Kickback is Calculated
Pedal kickback is derived from the chain growth divided by the chainring radius, converted to crank rotation.
To calculate pedal kickback, you need: the rear axle path (from the linkage geometry), the chainring tooth count, the cassette cog tooth count, and the crank length. The chain growth (ΔL) at each point in the travel is found by comparing the BB-to-axle distance at full extension versus the current compression state.
Pedal Kickback (°) = (ΔL / r_chainring) × (r_chainring / r_crank) × (180 / π)
Simplified:
Pedal Kickback (°) = (ΔL / r_crank) × (180 / π)ΔL = chain growth (mm) · r_chainring = chainring radius (mm) · r_crank = crank length (mm)
The gear ratio between chainring and cassette matters because it determines how much chain length corresponds to a given crank rotation. In an easier gear (larger cassette cog), the same chain growth produces less crank rotation because the cassette cog has a larger radius.
Real-World Impact
Pedal kickback matters most on rough, fast descents where the suspension is constantly cycling through its travel.
On smooth terrain, pedal kickback is rarely noticeable because the suspension is not compressing rapidly. But on rough, rocky, or rooty descents — especially at speed — the suspension compresses and extends constantly. Each compression event sends a kick through the cranks, which can:
- 1Disrupt foot position and cause the rider to feel chatter through the pedals
- 2Create fatigue in the rider's ankles and knees over long descents
- 3Reduce suspension effectiveness — the chain tension resists compression, effectively stiffening the shock
- 4Interfere with pedalling inputs — the rider's intended pedal stroke fights against the kickback
The threshold at which pedal kickback becomes noticeable varies by rider. Some riders are very sensitive to even 5° of kickback; others do not notice until 15° or more. Generally, keeping kickback below 10–12° at typical riding speeds is considered a good target for trail and enduro bikes.
Reducing Pedal Kickback
Designers use several strategies to minimise pedal kickback while maintaining acceptable Anti-Squat.
- 1Lower the main pivot: Reduces chain growth and kickback, but also reduces Anti-Squat. Must be balanced against pedalling efficiency.
- 2Use an idler pulley: Routes the chain line closer to the pivot to reduce chain growth. Common on high-pivot downhill bikes.
- 3High-pivot designs with idlers: Move the rear axle's arc centre closer to the BB, minimising distance change. Very effective but adds complexity.
- 4Gear selection: Riding in easier gears (larger cassette cogs) reduces kickback — the derailleur absorbs more growth.
- 5Clutch derailleur: Helps manage chain slack but does not eliminate kickback from chain growth.
Pedal Kickback in BikeSPEZL
The R&D module calculates pedal kickback for every gear, at every point in travel, based on your linkage geometry and drivetrain.
In BikeSPEZL's Ride Dynamics simulation, pedal kickback is computed from your KinematicDesign pivot positions (which define the axle arc path), the drivetrain settings (chainring teeth, cassette cog, crank length), and the current gear selection. As you adjust pivots or change gears, the kickback curve updates in real time, showing exactly where chain growth is occurring and how it translates to crank rotation.