Suspension Kinematics

Summary

Kinematics in bicycle suspension refers to the motion behavior of the rear axle and shock as the suspension compresses and rebounds. It defines how forces are transmitted through the frame and links — affecting pedaling, braking, traction, and overall ride quality.

Key Facts

  • Category: Concepts
  • Also known as: Suspension kinematics, linkage kinematics
  • Used by / Found on: Full-suspension mountain bikes
  • Related systems: Anti-squat, leverage rate, axle path

Overview

Kinematics is the foundation of modern rear suspension design. It describes how the moving parts of a full-suspension frame — particularly the rear triangle, linkages, and shock — behave under compression. Kinematics is not about the damper settings or shock internals themselves, but rather how the frame and linkage system guide suspension travel.

Every multi-link or single-pivot bike has a defined suspension curve — a result of its kinematics. This curve determines how efficiently the bike pedals, how much traction it has over rough terrain, how it reacts under braking, and how it feels deep in its travel. Core kinematic characteristics include leverage rate, axle path, anti-squat, and anti-rise.

Kinematics is where engineering meets ride feel. Designers use software modeling and real-world testing to tune a bike’s behavior across its travel. Well-optimized kinematics can make the difference between a bike that feels sluggish and inefficient and one that climbs crisply, corners confidently, and descends with control.

Though often invisible to the rider, suspension kinematics are among the most critical factors in how a bike performs — especially in trail, enduro, and downhill categories.

How It Works

Suspension kinematics involve the paths and mechanical advantages defined by the bike’s linkages as the rear wheel moves through its travel. These characteristics are defined at the design stage and are shaped by the pivot locations, link lengths, and frame geometry. Here are the core concepts:

1. Leverage Rate

The leverage rate defines how much the rear wheel compresses the shock throughout its travel. It’s expressed as a ratio — for example, 2.8:1 means that for every 2.8 mm of rear wheel travel, the shock compresses 1 mm. The leverage curve shows how this ratio changes through the travel.

  • Progressive Rate: Starts higher and decreases. Common in bikes meant for aggressive riding, this helps with mid-stroke support and bottom-out resistance.
  • Linear Rate: Constant through the travel. Found on some XC and trail bikes for predictable feel.
  • Regressive Rate: Starts low and increases. Rarely used in modern bikes, as it can lead to a harsh or uncontrolled end-stroke.

Most modern suspension systems aim for a progressive or lightly progressive curve, allowing for small-bump sensitivity off the top, support through the mid-stroke, and ramp-up at the end.

2. Axle Path

Axle path refers to the route the rear axle takes as the suspension compresses. It has a direct impact on how the bike handles square-edge hits, maintains speed through choppy terrain, and behaves under braking.

  • Vertical Axle Path: Seen in most single-pivot designs. Simple and predictable but can hang up on impacts.
  • Rearward Axle Path: Moves the axle slightly back before curving forward. Found in many dual-link and high-pivot designs, it allows the wheel to move away from obstacles, improving momentum and tracking.
  • S-Shaped or Curved Path: Typical in systems like VPP or DW-Link. These combine a slight rearward movement early in the stroke with forward movement later, giving a balance of bump compliance and geometry control.

The shape of the axle path influences how the suspension absorbs impacts, particularly square-edge bumps and repeated hits at speed.

3. Anti-Squat

Anti-squat is a measure of how much a bike’s suspension resists compression under pedaling. When you push on the pedals, the chain tension pulls on the rear triangle, and the suspension either stays firm, compresses, or extends slightly depending on the layout.

  • 100% Anti-Squat: Pedal input and weight shift cancel each other out. Neutral behavior.
  • >100% Anti-Squat: Bike stays firm under power. Reduces pedal bob and improves climbing.
  • <100% Anti-Squat: More active suspension under pedaling. Better traction, but may feel less efficient.

Designers tune anti-squat to be higher in the first third of the travel for efficiency and lower deeper in the stroke to allow the suspension to stay open for traction.

4. Anti-Rise

Anti-rise is the braking equivalent of anti-squat. It describes how the suspension reacts when the rider applies the brakes. This has a direct effect on traction and handling during descents.

  • High Anti-Rise: Keeps the rear suspension from compressing under braking. Stable but can feel harsh.
  • Low Anti-Rise: Allows suspension to remain active when braking, helping the tire maintain grip on rough terrain.

The ideal anti-rise value depends on the bike’s intended use. Some downhill and enduro bikes aim for active braking to maintain grip, while others prefer more stability at the cost of traction.

5. Instant Center and Virtual Pivot

In a single-pivot bike, the rear triangle rotates around one fixed point. In multi-link bikes, however, the rear end moves in a more complex way, controlled by two or more links. The intersection of these links’ paths forms an “instant center” — a moving point around which the rear triangle effectively rotates at any given moment.

This dynamic pivot allows designers to fine-tune the suspension’s response throughout the travel. For example, it lets them start with high anti-squat early in the stroke and lower it later, or create a rearward axle path at the beginning of travel without sacrificing end-stroke geometry.

Virtual pivot systems like VPP, DW-Link, and Switch Infinity all rely on the position and movement of the instant center to shape the bike’s behavior.

Notable Implementations

  • DW-Link (Pivot, Ibis): Uses precise link placement to manage axle path and anti-squat for efficient pedaling and controlled traction.
  • VPP (Santa Cruz): Dual counter-rotating links shape a balanced leverage curve and dynamic axle path for a firm pedaling platform and strong descending performance.
  • Switch Infinity (Yeti): A translating lower link maintains consistent anti-squat characteristics through the stroke, combining support and traction.
  • Maestro (Giant): A four-bar layout that offers a consistent leverage rate and active suspension under braking and acceleration.
  • Horst Link (Specialized): A chainstay pivot layout that isolates braking forces and maintains suspension activity under deceleration.

Related Terms

References

  • Linkage Design Software White Papers
  • Pinkbike: “Kinematics Explained” Series
  • BikeRadar Suspension Glossary
  • Manufacturer Tech Docs: Pivot, Santa Cruz, Yeti, Giant
  • Interviews with Dave Weagle and Cesar Rojo
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