Q:

What is an automatic overdrive transmission?

A:

Quick Answer

Overdrive in an automatic transmission allows the car to travel at the same speed using less power, making it more economical on fuel. By using a gear that turns the transmission faster than the engine, overdrive allows the engine to turn fewer times, saving on wear and fuel.

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Full Answer

Most cars with automatic transmissions have overdrive as their highest gear. For four-speed transmissions, overdrive is equivalent to a fifth gear, which engages only as the engine's rpms reach a certain level in the drive, or fourth gear.

Some cars have overdrive switches, labeled O/D, which can be turned on or off, though most sources advise leaving it on at all times other than when towing a load or navigating up and down steep hills. In those situations, the overdrive switch allows the driver to disengage overdrive to keep the engine from over-revving or to allow the gears to be used for braking.

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