Differential — How It Works

When a vehicle turns a corner, the outside wheel has to travel a longer distance than the inside wheel. If both wheels were locked together on the same shaft, one of them would have to scrub and skip across the pavement during every turn. The differential solves this by allowing the two drive wheels to rotate at different speeds while still receiving power from the same source.

The driveshaft turns a pinion gear. The pinion meshes with a large ring gear mounted in the differential housing. The ring gear turns at a different speed and angle than the pinion — this is the gear reduction that multiplies torque. The gear ratio — like 3.73 to 1 — means the driveshaft turns 3.73 times for every one rotation of the ring gear and wheels. Lower numerical ratios like 2.73 give better fuel economy. Higher ratios like 4.10 give more torque multiplication for towing and acceleration.

Inside the differential carrier, a set of spider gears — also called side gears and pinion gears — sit between the two axle shafts. During straight line driving, the spider gears do not rotate on their own axis — they just carry power equally to both wheels. During a turn, they rotate and allow the outside wheel to speed up while the inside wheel slows down. The total speed always equals the input speed — what one wheel gains, the other loses.

A standard open differential sends power to the wheel with the least resistance. If one wheel is on ice and the other on dry pavement, all the power goes to the wheel on ice — it spins uselessly while the other wheel sits still. A limited slip differential uses clutch packs, viscous fluid, or gear-based mechanisms to limit the speed difference between the two wheels. When one wheel starts to slip, the limited slip transfers torque to the wheel with traction. Limited slip differentials require specific friction-modified fluid — using standard gear oil causes chatter during turns.