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HomeTips & GuidesTransmission Overdrive: Automatic Gearbox Shifting Optimization for Fuel Economy

Transmission Overdrive: Automatic Gearbox Shifting Optimization for Fuel Economy

The transmission overdrive feature is on by default in automatic vehicles, and this implementation is on purpose because it reduces fuel consumption.

Manual transmissions differ from automatics because the driver can engage transmission overdrive by shifting to the higher gears.

We will explain why you should leave this feature on, its benefits, and the situations warranting its deactivation. Let’s get right into it!

Table of Contents

What Is Transmission Overdrive?

Transmission overdrive is a typical feature in automatic vehicles to help you improve fuel efficiency. It refers to the highest gears in automatic transmissions that keep the engine RPM lower than the wheel or gearbox output RPM.

Therefore, the feature optimizes the gearbox operations to maximize fuel economy, and turning it off makes the vehicle inefficient because it won’t operate at the highest gear possible.

If you’ve driven a manual vehicle, you know the shifting trick of maintaining the highest gear when cruising to keep the revs low and burn less fuel. Modern transmissions usually have two or more overdrive gears at the top of the range to help you achieve the same.

6-Speed Transmission Gear Ratios

In a 6-speed automatic, the overdrive gears are the top two (five and six). Therefore, when you disengage the feature, the vehicle will stretch the shifting from gear one to four. The system won’t recognize gears five and six.

This operation allows for faster acceleration and high torque but at the expense of fuel mileage. The vehicle will stop shifting once it gets to a 1:1 gear ratio (direct drive transmission gearing).

Here’s a gear ratio comparison for a 6-speed automatic transmission to drive the point home.

GearGear Ratio
1st gear3.24:1
2nd gear2.10:1
3rd gear1.42:1
4th gear (direct drive)1:1
5th gear (overdrive)0.82:1
6th gear (overdrive)0.62:1
Reverse3.67:1

A 1:1 gear ratio implies the engine (gearbox input shaft) and the gearbox output shaft are spinning at the same speed.

Therefore, automatic or manual transmissions with a 4-speed gearbox are not fuel efficient because they don’t have an overdrive ratio.

But it is vital to note that some 4-speed automatic transmission cars have this feature, which means the 4th gear has a ratio slightly lower than 1:1.

10-Speed Automatic Transmission Gear Ratios

Modern vehicles with additional gears spread the ratios more evenly, meaning they hit direct drive and overdrive at higher numbers. For instance, the 10-speed overdrive transmission in the Ford F150 has the following gear ratios.

GearGear Ratio
1st gear4.696:1
2nd gear2.985:1
3rd gear2.146:1
4th gear1.769:1
5th gear1.52:1
6th gear1.275:1
7th gear (direct drive)1:1
8th gear (overdrive)0.854:1
9th gear (overdrive)0.689:1
10th gear (overdrive)0.636:1
Reverse4.866:1

Why Use the Transmission Overdrive Function

The first and most obvious advantage is the increased fuel savings when cruising at highway speeds. At these low engine revolutions per minute, you will experience lower vibrations, engine noise, and harshness.

Lower fuel consumption automatically translates to reduced pollution. Cars can produce up to a third less emissions than driving with overdrive-off, making this feature eco-friendly.

An automatic transmission gear selector (note the overdrive button)

An automatic transmission gear selector (note the overdrive button)

Maintenance-wise, this feature prolongs the lifespan of motor parts because it reduces engine wear. Components such as the fuel pump, alternator, AC compressor, and water pump will last longer.

Transmission overdrive has no downsides, which explains why it is the default setting in automatic transmission vehicles.

But you should be careful when upshifting in manual transmissions because braking or slowing in fifth or sixth gear can lug the engine. Engine lugging can damage the gearbox or motor. 

You should downshift, put the car in the neutral gear position, or press the clutch pedal when braking.

When To Turn Off Transmission Overdrive

Although it has zero cons, you might have to turn off transmission overdrive in the following scenarios.

When on a Steep Ascent or Descent

Switching to lower gears gives you more torque, which you need when going up a steep hill.

However, it is not compulsory to switch transmission overdrive off because modern vehicles can figure out if the increased load requires lower gears. But turning off the feature ensures you only get the lower gears for maximum torque.

A traffic sign indicating a steep hill ascent ahead

A traffic sign indicating a steep hill ascent ahead

However, turning off the transmission overdrive is necessary when driving down a steep hill to get the engine braking power. Engine braking relieves pressure from the brakes, reducing overheating or wearing out of the pads/drums.

Manual transmission car drivers have perfected this art and can use the first gear down steep hills to keep their foot off the brake pedal.

When Overtaking

Vehicle computers are intelligent enough to know when to downshift automatic transmissions to provide the required torque when overtaking. They sense the throttle position and downshift if you press the gas pedal firmly.

However, you can take matters into your own hands by deactivating transmission overdrive.

This action will give you more control over the vehicle, especially when towing or carrying a heavy load, because you need maximum torque to pass the car in front.

A vehicle towing an old RV

A vehicle towing an old RV

When the Overdrive Dashboard Light Flashes

The overdrive feature has a dashboard light that turns on when you deactivate the feature. When the function is stable, it operates in either an on or off state, meaning the light will be off when overdrive is active and on when inactive.

The transmission overdrive off dashboard light warning

The transmission overdrive off dashboard light warning

But when it blinks, the feature is in a third state known as malfunctioning. It could be due to issues like ATF leakage, faulty solenoid control valves, or transmission fluid blockage during exchange.

And it is better to turn off the system and visit an auto repair shop ASAP.

How To Turn Off Transmission Overdrive

Automatic transmissions have a transmission overdrive button on the gear selector. But some cars have lower gears, usually one and two, marked on the gear selections.

This system gives you more control over your automatic gearbox because you can lock it in gear one or two. But it won’t shift past that. You’ll have to move the selector back to D.

Some advanced vehicles make the overdrive disabling feature easier using paddle shifters. Conveniently located right behind the steering wheel, these paddle shifters make it easy to downshift to lower gears, especially when overtaking, sending more torque to the wheels.

If you like pushing your car to the limits using an automatic transmission, we recommend getting one with paddle shifters.

But with the traditional automatic overdrive systems, you press a button on the gear selector to activate or deactivate the feature.

An automatic gearbox gear selector

An automatic gearbox gear selector

Once pressed, the button has a mechanical linkage or electronic solenoid that locks the automatic transmission to the direct drive (1:1) maximum.

Wrap Up

Modern automobiles might not feature a true overdrive feature because they have more gears or other more convenient alternatives for manual shifting, such as paddle shifters.

But the first generations of automatic vehicles that ushered out manual gearboxes needed this feature to reduce fuel costs.

Automatic gearboxes have other noteworthy features, and you should check out this torque converter lockup article to learn more about these transmissions.

That’s it for now. Comment below if you found the article insightful. We appreciate your feedback.

I am Lillian Yang, having been a sales manager for over 10 years.

I have received many positive reviews from customers. They have praised our excellent service, on-time delivery, and high-quality cable assemblies.

For your projects, please provide cable assembly files/images/smples, etc., so that I can send you a quotation within 24 hours.

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