Why can a car's wheels turn at different speeds in a bend?
In every corner your outer wheel travels farther than your inner wheel, yet both are driven by one engine. A set of gears sorts it out.
▶ Start the storyA car's wheels can turn at different speeds in a bend because of a set of gears called a differential. In a corner, the outer wheels must travel farther than the inner wheels, because they are on a larger radius. That is easy when wheels are not connected. It is harder for the drive wheels, because both are connected to the engine through the transmission. A differential is a with three shafts, built so that the speed of one shaft is the average of the speeds of the others. In a car it lets the wheels at each end of a rotate at different speeds while cornering.
Picture two runners on a curved track holding the ends of a rope. The runner on the outside has to cover more ground in the same time. The differential lets one wheel gain turns while the other loses them, while the engine's push is still shared between them.
Outer wheel
- Travels farther in a bend
- Needs to turn faster
Inner wheel
- Travels a shorter path
- Needs to turn slower
Some vehicles manage without one. Go-karts and trams use axles without a differential, and rely on wheel slip when cornering. Until the late nineteenth century most steam road vehicles used a clutch on each driven wheel, engaged or not as required. Carl Benz built one into his belt-driven Patent-Motorwagen in 1885.
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Recap
The outer wheel goes farther, so it must turn faster, and the differential lets it.
💡 A trick to remember it · Like runners on a bend, the outside one runs more and the inside one less, but they still share the effort.
Surprising fact · It was first used in clocks, long before cars.
Sources (1)
No source, no claim. Every fact in this lesson (16 claims) cites at least one of these.