Final Drives & Differentials

01Definition

The final drive is the last gear reduction in a driveline, sitting right at the wheel hub or track sprocket, where the very highest torque and lowest speed in the whole machine are required. The differential, usually just upstream of it, allows the two output shafts to spin at different speeds — essential the moment the machine turns a corner.

02Physical Principle

An engine spins fast but with comparatively little torque; a final drive's job is to spend the last, steepest gear reduction of the whole driveline turning that speed into torque, right where the ground finally meets the machine. A differential solves a problem final drives alone can't: in a turn, an outside wheel or track must travel farther, and therefore faster, than the inside one, so the differential splits incoming torque between two output shafts while letting them rotate independently — normally, at the cost of always sending more torque to whichever wheel spins easiest, which is why heavy machines add lockable or limited-slip differentials for low-traction ground.

03Mathematical Foundation

04Interactive Diagram — Final Drive & Differential

Set the final-drive ratio and toggle cornering to see the differential let the outer wheel spin faster than the inner one.

05Interesting Facts

• A locked differential sends equal torque to both sides regardless of traction — essential in mud or on a slope, but it fights the machine on a hard-surfaced turn and is disengaged as soon as traction allows.
• Tracked machines like bulldozers and excavators don't use a differential in the wheeled sense at all — each track has its own final drive, and steering comes from slowing or reversing one side.
• A final drive failure is one of the most expensive repairs on a mining haul truck, because the whole reduction gearset sits sealed inside the wheel hub, submerged in gear oil, exactly where dirt and heat both concentrate.

06Real-World Applications

07Related Concepts