Overdrive definition and meaning
Overdrive is a feature in many modern cars that allows the engine to run at a lower rpm for a given road speed. This can improve fuel economy and reduce engine noise. Overdrive is typically engaged by selecting a higher gear ratio on the transmission, such as fourth gear instead of third. This can be done either manually or automatically.
When overdrive is engaged, the engine speed will decrease for a given road speed. For example, if you are driving at 65 mph in overdrive, the engine may only be running at around 1500 rpm. In a lower gear, the same car would be running at around 2000 rpm at 65 mph.