What Does Overdrive Do? (and When To Use)

Is your car’s overdrive function still a mystery? You’re not alone. Many drivers don’t understand what overdrive does or when to use it.

In this article, we’ll shed light on the purpose of overdrive gears and explain how they can boost fuel economy when used properly. We’ll go over when you should turn overdrive on for highway cruising and off for more power in hills or passing.

what does overdrive do

Related: Does Cruise Control Save Gas?

What is Overdrive?

The term “overdrive” refers to the highest gear that you can shift to in some automatic transmission vehicles. Almost all vehicles on the road today feature at least one overdrive gear within the transmission.

This gear allows the engine to operate at a lower RPM (revolutions per minute) than normal gearing. This helps improve fuel efficiency when driving at higher speeds.

The key features of overdrive are:

  • It is a higher gear ratio than 1:1 direct drive, usually between 0.7:1 and 0.8:1. This means the output shaft turns slower than the engine’s rpm.
  • It only engages at higher vehicle speeds, typically above 45-55 mph. At lower speeds, overdrive disengages and normal gears are used.
  • It reduces engine RPM at highway speeds, allowing more efficient operation and improved fuel economy. You won’t be wasting gas when there’s no need for performance.
  • The lower engine speed also reduces wear and noise. Driving is quieter and smoother.
  • Overdrive doesn’t increase vehicle speed, it just allows the same speed while using a higher gear so the engine works less.

When to Use Overdrive

when to use overdriveIf your automatic transmission vehicle has a manually selectable overdrive gear, you will often need to push a button to activate. Once that button is pressed, the transmission upshifts to the highest gear possible.

This button is meant to be pressed while you’re driving at a consistently high speed because it will take the strain off the engine by lowering its RPM. Basically, the overdrive allows the engine power to go right to the transmission while locking the torque converter. This will improve the performance of the vehicle and save you money on fuel at the same time.

To give you an example of a good time to use overdrive, let’s say you’re driving over 60 miles per hour on the interstate. At this speed, the RPM of your engine is going to increase depending on your vehicle’s gear ratios and the number of gears it has. Higher speeds usually put more strain on your engine.

Because there is more strain, it will require more fuel to be consumed just to meet the demands of the pressure being put on it. If you were to activate overdrive or economy mode, the strain would be alleviated from the engine because its RPM would be lowered. Then, your fuel economy will be improved.

The times you don’t want to use the overdrive is when you’re traveling at slower speeds, typically under 50 miles per hour or expect you’ll need to accelerate quickly such as when passing another vehicle.

If you were to activate overdrive at a lower speed like this, it would cause your vehicle’s speed to become very inconsistent and dangerous. This goes double for people who normally drive around town or through the streets of their city.

Add-On Overdrive

If your older automatic transmission vehicle does not have an overdrive gear, it is possible to attach an add-on overdrive to your existing transmission in order to give it one. Truckers would call add-ons like these “splitters.”

The unit is really just a smaller transmission with 2 speeds that gets bolted onto the back of your vehicle’s main transmission. With this add-on, your vehicle will be able to cruise at higher speeds with more fuel efficiency just like any other car with overdrive in it.

The term “2-speed” really means it will double the speed of your existing transmission. So, if you have a 3-speed transmission, then it will turn it into a 6-speed transmission. If you have a 4-speed transmission, then it will turn it into an 8-speed transmission.

But you don’t really need to concern yourself with this because you will experience fuel efficiency regardless of what speed your current automatic transmission is at.

Overdrive Add-On Cost

If you’re looking to purchase an overdrive add-on kit, you will find them priced anywhere from $800 to $3,000. There are instructions which come with the kit that can help you install it.

However, if you don’t have enough mechanical skill to install it yourself, you should definitely hire a professional. This will run you another $200 to $400 in labor costs.

Mark Stevens


  1. I’m still a little confused. Do I have to use this manually or is this automatic.
    (I push the button on the gearshift and nothing is shown on my screen.) I have a 2022 Volkswagon Teos.

    1. Overdrive is the top gear of an automatic. You don’t have to do anything to use it. Some vehicles have an Overdrive Off button (sometimes abbreviated O/D OFF). When you press this, it will lock the transmission out of the top gear. In a four speed automatic, this would limit the vehicle to gears 1-3.

  2. I own this button in my 2017 Nissan Altma. I don’t know how and when to use it. I usually drive the car at normal gear speeds. Is it necessary to use this button on public highways with high speeds?

    1. The overdrive gear is a gear for fuel economy, typically seen on four speed automatics. In this case, the overdrive gear would be the fourth or top gear.

      If you’re on the highway and you push the overdrive button, you should feel and hear your car downshift. Pushing this button kicks you into third gear, which is better for acceleration. This can be useful on hills, for instance.

      Some dashes illuminate “overdrive” when the button is pressed, which is confusing. Other vehicles say “O/D Off”, which is a more accurate label in my opinion. Pushing the button essentially locks the car out of top gear so it’s not shifting back and forth a bunch if you’re trying to maintain a constant speed on a hill.

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