Overdrive definition
A unit with a planetary gearset which turns the driveshaft faster than the transmission output shaft . Sometimes the overdrive is an additional gearbox which is mounted in the driveline . Normally the final drive ratio is 1:1; but the overdrive makes it less (e.g., 0.87:1). The overdrive can reduce gas consumption at sustained high-speed driving, engine noise, and engine wear. Also called "overdrive transmission."