What does a differential do?

Lets the two driven wheels spin at different speeds in a turn. In a turn, the outside wheel travels further than the inside wheel. A differential is a clever gearbox that lets the two wheels on one axle spin at different speeds, so the car turns smoothly without skidding.

Try Differential Demo Cart for free

Complete MightyCog booklet collection: 82 PDF booklets for $12.99. Instructions only; individual booklets remain free.

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Try it yourself

Lift the racer, hold one back wheel still and turn the other. What does the differential do?

Build it: 7 builds that teach the differential

  • 🔀 Differential Demo Cart: Push it round a corner and watch: the outside wheel spins faster than the inside one! (level 2 of 5, about 22 minutes, 10 steps)
  • 🌀 Pull-back Diff Racer: A spring racer with a real differential, so it zooms round curves without skidding. (level 3 of 5, about 40 minutes, 23 steps)
  • 🔒 Diff-Lock Mud Truck: Stuck in the mud? Slide the diff lock and both wheels are forced to turn together! (level 4 of 5, about 60 minutes, 33 steps)
  • 🏆 RC Racer: A real remote-control car: motor drive, differential, servo steering and headlights. (level 5 of 5, about 75 minutes, 38 steps)
  • 🏆 Independent Rally Car: Every wheel on its own springy arm, a differential, universal joints and Ackermann steering. (level 5 of 5, about 90 minutes, 47 steps)
  • 🌐 AWD with Central Diff: All four wheels driven, with a differential in the MIDDLE of the car — like a rally car. (level 5 of 5, about 90 minutes, 28 steps)
  • 🧭 South-Pointing Chariot: Push it anywhere — the pointer keeps pointing the same way. No magnets, just gears! (level 5 of 5, about 75 minutes, 34 steps)

In the classroom

Common engineering questions

How can I try the differential at home?

Lift the racer, hold one back wheel still and turn the other. What does the differential do?

Which builds teach the differential?

7 MightyCog builds teach it: Differential Demo Cart, Pull-back Diff Racer, Diff-Lock Mud Truck, RC Racer and Independent Rally Car and more. Start with Differential Demo Cart: 10 steps, about 22 minutes.

Ideas that go with it