Drive Gear

How to properly use the over-drive mode on automatic gear boxes

Some people (especially elders) prefer driving automatic cars, as they are easier to drive. Many of the automatic gear boxes present a feature named “Over Drive“, feature that turned on or off usually via a button that is on the gear level.

Once pressed this button, a reduction mechanism is electronically activated at the exit of the gear box to reduce the engine rotations for the same speed of the vehicle.

As a consequence, turning the over-drive on is equivalent with using one level higher gear.

Why such a mechanism, and not yet-another gear level? Because it is complex to design gears with more levels, the constructor prefers reusing the old gear models, while installing the over-drive is not so expensive; however, it has some draw-backs: it cannot face great load as a normal mechanically switched gear, so you should never use it in the following conditions:

-          Slippery road;

-          Snow;

-          Climbing on mountains;

-          Dragging or carrying heavy load.

As the over-drive is switched electronically at the press of a button, many constructors limit this mode only at the highest gear level; also, the over-drive does not transmit all the engine torque to the wheels, hence, it is dangerous to use it in bad weather conditions, like rain or snow.

Moreover, you should never use the over-drive in load, including overtaking on the motorway, as the over-drive loses torque and the car is losing the potential to overtake.

With such limitations, do you really have to use this over drive mode?

The answer is yes, when you are running on the motorway, you are running fast and at constant pace, and you do not expect any heavy load on the engine – as strong winds, overtaking main oeuvres, or you expect to use the engine brakes while descending from mountains and hills, because the over drive mode is just a cheap low torque transmission reduction mechanism, in order to help you decrease the fuel bill, by 10%, and sometimes even 20-25%, especially if you are driving with more than 60 miles per hour.

For more information you may access http://www.freedrivingrules.com/news/110610224501/I have an Over Drive Gear Box – what does this mean, and from there you can read also related jubjects.

About the Author

Dragos-Matei Sorescu, Programming Engineer

Industrial Automation and Computer Science graduate in Bucharest, Romania.

GL1800 ADG (Alternator Drive Gear) Rattle