Technical Editor at CAR Magazine Nicol Louw has done some research and writing on what is termed an "overdrive" in a transmission.
Early vehicles came with an overdrive, is this still the case and why would you need an overdrive in the gearbox?
Our older listeners would know, 40 or 50 years ago, cars would come with three and four speed transmissions and you would get the option of overdrive...— Nicol Louw, Technical Editor at CAR Magazine
With modern transmission you do not get an extra box added to the gearbox....the older transmission there was actually a separate little transmission bolted to the four speed transmission that gives you one extra gear which would then be your fifth gear and it's called overdrive because the input would then be 0.8 revolutions for one output of the gearbox.— Nicol Louw, Technical Editor at CAR Magazine
The result is then that your engine speed is reduced for motorway cruising, it is better for fuel consumption, for NBH and so on.— Nicol Louw, Technical Editor at CAR Magazine
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This article first appeared on 702 : [LISTEN] Motoring: What is an overdrive and why would you need it?