Overdrive Mode in Automatic Transmissions

Some cars equipped with automatic transmissions have an operating mode named “overdrive” (or O/D) i.e. the highest gear. This mode can be considered as an analog of the 5-th gear in manual transmissions.

Inexperienced drivers often come up with the question of how to engage the overdrive mode? In fact, this mode can be activated with the help of the button located on the automatic transmission lever. In fact, the overdrive engagement is considered to be a standard state – when the overdrive is switched off, you can see a yellow indicator light on the dashboard with the corresponding caption (“O/D off”).

The overdrive mode is the highest gear in the automatic transmission with the gear ratio less than 1 – when this gear is engaged the driven shaft has higher speed than the drive shaft.

Learn more about the O/D mode in automatic transmissions

Pros and cons of O/D

When the overdrive button is pressed the car switches to more economical and convenient mode of gear shifting. In the process of acceleration, after you shift to the 4-th gear and actuate the O/D mode, the higher gear gets engaged automatically. At the same time, when the car decelerates the transmission shifts to a lower gear, and then again shifts to the optimal gear with further acceleration.

When the O/D mode is switched off, the process of gear shifting is performed at higher engine speed (RPM rate). In this case, if you press the brake pedal, the automatic transmission will operate at the same gear and it will downshift only when a certain speed and RPM rate are reached. When driving with the disabled O/D mode, your capacity to shift higher than the 3-rd gear will be blocked.

Difference between drive and overdrive

Based on the stated above, we can conclude that the O/D mode is necessary, first of all, to improve driving characteristics of the car. When the O/D gear is used properly, it can facilitate to more rational use of energy. In addition, usage of the overdrive slightly reduces the amount of exhaust emissions.

If you consider all pros and cons of the overdrive mode, we should mention the following:

• If the O/D mode is activated, then the 4-th gear is engaged as soon as possible, i.e. you can expect some fuel saving;
• Thanks to overdrive, the engine operates less in the high-speed mode – you prolong the engine service life;
• Operating manuals for different cars say that the O/D mode should be switched off under severe operating conditions. In this case, city driving with frequent stops, accelerations, overtaking maneuvers, lane changes can be considered as severe conditions;
• The automatic transmission more frequently shifts to the 4-th gear in the O/D mode, thereby increasing the wear of transmission mechanisms. When the overdrive is engaged, the engine braking can be not very efficient.

It becomes clear that the O/D mode can be very useful when driving at a highway with high speeds, because in this case the engine and the transmission operate at optimal capacity.

It is recommended to switch off the O/D mode when you perform a long-time overtaking at high speeds (higher than 100 km/h). In this case, short-time O/D switch-off can be done with the help of the kick-down, i.e. when the driver strongly and sharply presses the gas pedal. Also, it is better to switch off the overdrive when towing a trailer, driving on snowy and iced roads. If you need to use the engine braking, the overdrive also must be switched off. If we talk about everyday city driving, it is also better not to use the O/D button.

Overdrive and Fuel Consumption

Usage of the overdrive mode does not have any significant impact on the overall fuel consumption. Of course, it is possible to save some amount of fuel when you use the overdrive timely and properly (or on the contrary, disconnecting overdrive when necessary), but it will give you little benefit. Thus, we can say that the O/D mode does not have a significant impact on fuel consumption.

Overdrive Efficiency

The efficiency and relevance of the O/D mode use mostly depends on specific driving conditions– road surface, traffic congestion, and traffic density. There is no standard set of rules on the O/D mode usage, thus drivers should work out some terms of use depending on their driving style and experience. In other words, drivers of cars with automatic transmissions decide for themselves when and under what conditions to use this feature. Drivers should know how to use the O/D mode, switching it on and off depending on certain conditions.

So, let’s sum up when to use the overdrive and when to avoid use of this mode.

Great video with tips on O/D usage

It is recommended to engage the O/D mode to improve the driving comfort and car handling during long-term driving on highways with constant speed. It is also desirable to use the overdrive at high speeds (120 km/h and higher).

Do not use the O/D mode in following cases:

• Active driving at low speeds;
• Long-time downhill/uphill driving;
• Stop-and-go driving;
• Long-time overtaking at medium speeds;
• Towing a trailer/transportation of cargo.

Overdrive and Towing

The overdrive mode is a very useful feature which became indispensable for many drivers. However, you must get used to driving with overdrive; learn all pros and cons of this function, and remember to use it properly and timely. You will become comfortable with usage of the O/D mode, when you gain some experience of driving a car using overdrive in different conditions.