Here's how it works:
* 1:1 ratio: In a standard gear (like 4th gear in many older cars), the engine crankshaft and the output shaft of the transmission rotate at the same speed.
* Overdrive ratio: An overdrive gear ratio is less than 1:1 (e.g., 0.7:1). This means the output shaft rotates faster than the engine crankshaft.
The benefits of overdrive include:
* Improved fuel economy: Lower engine RPMs mean less fuel consumption.
* Quieter operation: The engine runs smoother and quieter at lower RPMs.
* Reduced engine wear: Less stress on the engine components leads to longer lifespan.
* Higher top speed (in some cases): The higher gear allows the engine to reach a higher speed before reaching its maximum RPM.
Overdrive is usually engaged automatically by the transmission in modern cars with automatic transmissions, or can be selected manually in some automatic and manual transmissions (often labelled "OD" or "O/D"). Disengaging overdrive can be useful for situations requiring more engine braking (like going down steep hills) or more power (like towing a heavy load).
