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Home/Classical Mechanics/Bicycle Stability (2D)

Bicycle Stability (2D)

Side view: roll dynamics with fork trail and gyroscopic wheel torques — see speed, trail, and ω = v/R vs lean.

4.5 m/s
52 mm
0.34 m
2.2 kg
0.28 m
82 kg
12 kg·m²
0.85 N·m·s/rad
6 °
Wheel ω = v/R13.24 rad/s
Linear margin (restoring − gravity)45.3 N·m/rad
Sketch v for stability (small φ)4.11 m/s

Shortcuts

  • •Space — start
  • •R — pause & reset

About this model

This simulator integrates a small-angle roll equation for a side-view bicycle sketch: gravity applies an overturning torque about the rear contact, while a trail-like term (∝ v²) models how steering geometry couples lean to a restoring moment, and an optional gyroscopic term scales with wheel spin Iω² ∝ (v/R)². It is a teaching cartoon, not a full Whipple–Carvallo model.

Who it's for: Intro mechanics and conceptual vehicle dynamics; comparing when gyroscopic effects matter versus geometric trail.

Key terms

  • caster / trail
  • gyroscopic moment
  • roll angle
  • critical speed
  • small-angle stability

How it works

Side-view caricature of bicycle roll: gravity tends to increase lean, while fork trail (caster) and spinning wheels add restoring torques that grow with speed. Real bicycles also weave and depend on rider input; this model isolates two textbook ingredients so you can see why a minimum speed helps and how trail and gyroscopic terms scale.

Key equations

Iφ̈ = mgh sin φ − β(v) v² φ − k_g I_w (v/R)² φ − cφ̇ (trail + gyro, small φ)

ω = v/R; larger trail and faster wheels raise the restoring stiffness at a given speed.

Frequently asked questions

Is this enough to explain a real bicycle staying up?
No. Real bicycles involve steer angle, frame compliance, tire slip, and rider control. Experiments show many bicycles can be self-stable in a speed window even with gyroscopic effects reduced, so trail and mass distribution matter a lot; this lab isolates two common textbook ingredients.