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Overdrive

Once upon a time, a car’s top gear ratio was rarely more than 1:1, meaning the wheels were turning at the same speed as the engine.

Now, with transmissions being built with five or more gears, most cars are able to have at least one overdrive gear – which might have a ratio of 0.75:1, for example – to reduce the speed the engine runs at while cruising and therefore reduce fuel consumption.

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