The Physics of Cycling
A bicycle is a physics laboratory you can ride. Gears, drag, rolling resistance and balance all show up within the first kilometer — and understanding them makes you measurably faster.
Gears are levers in a circle
A low gear gives high torque at low speed for climbs; a high gear gives speed at the cost of force. The gear ratio is just mechanical advantage: force × distance is conserved (minus friction).
Air drag dominates
Above ~15 km/h, aerodynamic drag exceeds rolling resistance. Drag ∝ v² means doubling speed needs ~8× the power (power = force × velocity, and force itself ∝ v²). Tucking low can save 20–30% of your effort.
Braking and weight transfer
Deceleration pitches weight forward onto the front wheel — which is why the front brake does most of the stopping but also why grabbing it too hard flips you. Modulate both, weight back on descents.
Balance is steering, not gyroscopes
The old 'gyroscopic stability' story is mostly myth: experiments show bikes stay up mainly through trail — the front wheel's contact point sitting behind the steering axis, which self-corrects like a shopping-cart caster.
Try this yourself
- Coast the same hill tucked vs upright and compare top speeds — that's drag.
- Count crank vs wheel revolutions in your lowest and highest gears to feel the ratio.