'What is an overdrive gear and when do I use it?' [Newbie Guide]

Updated Mar 01, 2021 | Same topic: Beginner's Guide

It’s more than just the title of a popular song.

You might have first encountered the term ‘overdrive’ while hearing the popular Eraserheads ditty about the joy of taking the wheel on a road trip. As you finally earned your driver’s license and your own car, you realize that it actually affects your driving more than you realize.

Overdrive automatic cars

No, it doesn't stand for "overdose"

The most notable thing about overdrive is not what it enables your car to do, but rather what it prevents your car from doing, which is to reach its potential top speed. Why would such a feature be included in a machine that’s built to go fast? The answer is simple: For efficiency.

When a car runs, the engine works within a very narrow powerband. The power that the engine produces rises only up to a certain point and then falls away.

In order to expand this to a more usable range, the transmission provides a set of gear ratios that allow for greater flexibility in using that power, without forcing the engine to reach its maximum revolutions per minute or RPM. The fastest was 1:1, also called the ‘direct-drive’, where the engine’s input and output are equal.

>>> Related: “What is an A/T shift lock and when do you use it?” [Newbie Guide]

Manual shift knob

The highest cog in manual transmission cars is designated as the overdrive gear

However, a higher gear became necessary that would make the transmission output shaft spin faster than the engine. This allowed the car to achieve cruising speed while reducing fuel consumption and increasing the engine’s lifespan. The new cog came to be known as the overdrive gear.

Instrument panel

More grunt is available to the car when overdrive is turned off 

In a manual transmission vehicle, the overdrive gear is simply the highest forward gear on your gearbox, just before the reverse gear. While modern automatic transmission vehicles already have the overdrive integrated inside the drivetrain, older models feature a physical button marked O/D on the shift lever.

Overtaking

Disengaging overdrive allows you to execute maneuvers such as overtaking

By default, this button should be engaged under normal driving conditions, as it allows the transmission to maximize the entire range of gears available to it. However, there are instances when the car needs to utilize more of the engine’s output, such as when overtaking or driving under full loads up a steep incline.

>>> Related: Overtaking rules in the Philippines every driver must know

Pressing the button turns off the overdrive gear and yields noticeably more power for this purpose but at the expense of higher fuel consumption and faster engine wear.

Find more helpful driving tips for new motorists at Philkotse.com.

Joseph Paolo Estabillo

Joseph Paolo Estabillo

Author

Joseph has been a member of various car clubs since he got his driver's license in 2004 – old enough to remember riding in taxicabs with analog meters, but his fascination with cars goes way back. After nearly two decades of working in broadcast media, he shifted gears by coming on board as Philkotse’s first Filipino member and staff writer in 2017.

Apart from his role in Philkotse as Content Team Lead, Joseph has written episodes for Drive, which has been airing on CNN Philippines for five seasons running. He has also delivered content for various car dealerships based in the U.S., spanning multiple brands such as Alfa Romeo, Maserati, Jeep, Dodge, among others.

Keeping his hopes high and his revs low, he dreams about owning a Kei car when he retires. Hates slow parkers.

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