What if there were no gears?

A gear is a wheel with teeth around the edge. When one gear turns, its teeth push the next gear around.

What if gears had never been invented?

A gear is a wheel with teeth around its edge. Put two gears together so their teeth fit, turn one, and the other turns too. If the two gears are different sizes, they turn at different speeds.

Gears and other toothed wheels turn inside clocks, bikes and many other machines. In this thought experiment, Olly imagines a world with no gears at all. What would bikes be like? How would clocks work? Choose a path to find out.

Encyclopaedia Britannica defines a gear as a toothed wheel on a rotating shaft; gears work in pairs to transmit and modify rotary motion and torque, or turning force, without slipping. OpenStax lists gears among the simple machines that multiply force, often at the cost of distance.

This thought experiment removes gears, and the related chain-and-sprocket drives that cyclists call gears, from three settings: bicycles, clocks and machines that need a strong turning force. Its predictions are reasoning, not tests, and are labeled as ideas.

A bike has a toothed wheel by the pedals. A chain links it to a small toothed wheel at the back.

In a clock, gears turn the hands at just the right speeds.

On a bicycle, your feet turn the pedals, which turn a toothed chainwheel. A chain carries the turning to a smaller toothed sprocket on the back wheel. Cycling UK explains that if the chainring is twice the size of the rear sprocket, the back wheel turns twice for every turn of the pedals.

In a mechanical clock, a row of gears called the train carries motion from a spring or a falling weight to the hands. The gears are sized so that the minute hand goes around once an hour, and a 12-to-1 set of gears turns the hour hand once every 12 hours.

Britannica explains that if a driven gear has twice as many teeth as its pinion, it delivers twice the torque at half the speed; with the pinion on the driven side, the pair instead increases speed and reduces torque. A bicycle's chainring and rear sprocket do the same through a chain: Cycling UK gives a 48-tooth chainring and a 16-tooth sprocket as a 3:1 ratio, three wheel turns per crank turn.

In a mechanical clock, the wheel train transmits motion from a weight or spring, through the escapement, to the hands. One arbor, usually the second or third, turns once an hour to carry the minute hand, and a 12-to-1 'motion work' steps that down for the hour hand.

With no gears, a bike's pedals would have to turn the wheel straight on.

A clock's minute hand and hour hand might not be linked. Things might get much harder!

Take the chain and its toothed wheels off a bike, and the pedals have to be fixed straight onto a wheel. That's how the first pedal bikes worked. Each turn of the pedals turned the wheel just once, so the only way to go farther with each pedal turn was a bigger wheel. That is why the tall penny-farthing was built.

Without gears, a clock might struggle to turn its minute hand once an hour and its hour hand once every 12 hours from one spring. And machines that need a strong, slow turn, or a fast, light one, might need a different motor for every job.

Cycling UK notes that the first pedal cycles had cranks fixed to the front wheel, so the distance per crank turn was set entirely by the wheel's size; a bigger wheel went further per turn, which is why penny-farthings arose. A penny-farthing with a 52-inch wheel had a '52-inch gear', the same distance per crank turn as a 26-inch-wheeled bike with a 2:1 chain drive.

The rest is reasoning, labeled as ideas: without gears, a clock might lose the fixed 12:1 link between its hands, and machines might lose the easy trade between speed and torque that a gear pair gives, needing belts, levers or differently sized motors instead.

A small gear turning a big gear makes a slow, strong turn. A big gear turning a small gear makes a fast turn.

Gears swap speed for strength.

When a small gear turns a big one, the big one turns more slowly but with more turning force. When a big gear turns a small one, the small one spins faster but with less force. Gears let one motor or one pair of legs do very different jobs.

That's why bikes have low gears for hills and high gears for going fast. Cycling UK explains that a low gear lets you ride slowly uphill while pedaling at an easy pace, and a high gear lets you go fast, downhill for example, at an easy pace too. But gears never make energy: a stronger turn is always a slower one.

For a gear pair, the speed ratio is the inverse of the tooth ratio and the torque ratio equals it (ignoring friction), so power, torque times angular speed, passes through unchanged. A machine cannot do more work than the energy put in (OpenStax); gears only redistribute it between speed and torque.

This is what makes gear trains so useful: a motor or a rider can work at a comfortable speed while the output turns as fast or as slowly as the job needs. In a bicycle the lowest gear pairs the smallest chainring with the largest sprocket, and the highest gear the largest chainring with the smallest sprocket (Cycling UK).

Gears have been used in clocks for hundreds of years.

A very old clock in England, at Salisbury Cathedral, is from 1386.

The oldest surviving clock in England, at Salisbury Cathedral, dates from 1386, according to Encyclopaedia Britannica. Early tower clocks like it were driven by falling weights and only struck the hours. They had no hands or dial at all.

Bikes tell a different story. The penny-farthing's giant front wheel was a way to go farther with each pedal turn without any gearing. Cycling UK shows what a chain changes: a bike with 26-inch wheels, geared 2 to 1, goes as far with each pedal turn as a penny-farthing with a 52-inch wheel.

Britannica dates the oldest surviving clock in England, at Salisbury Cathedral, to 1386. The first mechanical clocks to which clear references exist were large, weight-driven turret clocks that struck the hours and had no hands or dial; the first spring-driven clocks, from about 1450, usually carried an hour hand only, and minute hands did not become general until the 1650s.

Cycling UK sets the two side by side: on a penny-farthing, wheel size was gear size, while on a chain-driven bike the chainring and sprocket set the distance per crank turn, so a 26-inch wheel driven 2:1 travels as far per turn as a 52-inch penny-farthing.