Overdrive is a mode that lowers RPMs in higher gears to save gas at higher speeds. By improving fuel economy and reducing noise while cruising, overdrive is an easy way to decrease wear and tear. Both manual and automatic cars can have overdrive.

While it sounds like a futuristic science fiction term—“Engage overdrive! Full speed ahead!”—overdrive is actually a pretty old invention. Automotive engineers back in the 1930s and 1940s started to look into ways to protect a car’s engine and save gas while driving faster.

Today, overdrive is standard on most automotive vehicles. In fact, your Toyota or Ford (or another model) may even engage overdrive automatically to help you conserve fuel. So how does overdrive work?

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What does overdrive do?

Overdrive is a gear reduction system that can decrease an engine’s RPMs (revolutions per minute) in higher gears. The overdrive unit is used to improve performance while highway driving.

Once your vehicle enters this low RPM mode, the vehicle is considered to be over-geared or overdriven. The outcome is less power but more efficient cruising, reducing fuel consumption during long-distance drives at high speeds.

The top benefits of the overdrive function are better fuel economy, reduced engine wear, and quieter operation.

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How does an overdrive system work?

Let’s start by understanding how a transmission works without overdrive.

A standard vehicle operates in a lower gear with more torque and power output. Without outdrive, the transmission stays in lower gears and remains highly responsive to the accelerator and the engine brake. The top gear in older cars had a gear ratio of 1:1 (aka direct drive), which tends to produce unpleasant noise and unnecessary fuel waste.

However, when you operate with overdrive, you multiply the torque thanks to an additional gearing unit on the gearbox. Overdrive produces a situation where the input shaft is rotating slower than the output shaft.

Think of overdrive as a higher gear mode that increases the shifting range at the top of the transmission’s capacity. So, overdrive gear helps you achieve the highest gear with a low gear ratio. By allowing your vehicle to shift higher, the powertrain can reach lower gear ratios (less than 1:1). Remember, the higher the gear, the better fuel efficiency you will enjoy at cruising speed!

In very old cars, a driver could take their foot off the gas pedal to switch to overdrive and press again to disengage. In cars from the 1980s and 1990s, the overdrive system can be triggered with an overdrive button near the shifter. The button is usually labeled “OD” or has an icon of a car climbing a hill. An “O/D off” code may appear on the instrument cluster when overdrive mode is deactivated.

In modern cars, overdrive is automatically engaged when the car’s Engine Control Unit (ECU) determines that the right conditions are present.

Overdrive in manual vs. automatic cars

Both manual and automatic transmission cars can have overdrive systems. However, the number of gears and the method of engagement depend on the specific vehicle and how the torque converter works.

For example, in a five-speed manual transmission, overdrive is the fifth gear here. In a six-speed transmission, overdrive gear is the sixth. Manual cars require the driver to engage overdrive manually using the stick shift and the clutch.

With an automatic transmission, the overdrive system will kick in automatically as needed when the on-board computer sends a signal. Then, the input-to-output ratio changes so that the output shaft moves faster than the engine. In other words, there are more revolutions going out than being taken in. As a result, you can cruise at a higher speed while your engine speed is slower.

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When to use overdrive

If you drive an automatic vehicle, then overdrive is always active. You should leave it on so that it can activate as needed.

If you drive a manual vehicle, then you will engage the overdrive high gear as you shift to higher speeds while accelerating. Overdrive should only be used when driving at least 50 mph on the highway, where high speed will be maintained for some time.

When to turn overdrive off

Because overdrive sacrifices power and speed, there are a few situations in which you should turn overdrive off:

When passing another vehicle

When climbing a hill

When descending a steep hill

When towing a heavy load

When driving on off-road surfaces

Note that using a lower gear improves your braking ability—so you should turn overdrive off when going up or down a hill. That’s why “overdrive off” mode is called “grade assist” in some vehicles.

It’s very important to know how to use overdrive safely. If overdrive is turned on, you won’t have the full power of your vehicle. As a result, you may struggle to pass a vehicle or handle a gravel road—either of which could result in a dangerous outcome.

MORE:

Highway driving tips for safe and smooth travel

How to find hassle-free car insurance

Learning about your car is a lifelong undertaking. From overdrive to tire pressure, your vehicle has a ton of nitty-gritty specifications that require painstaking attention to detail.

If learning about your car is your passion, that’s fantastic! Some people love to spend hours and hours on their passions. However, we’re willing to bet that car insurance probably isn’t your passion.

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FAQs

What is the difference between overdrive and cruise control?

Cruise control maintains the speed and throttle more consistently than a human driver could. It keeps the car moving at a speed set by the driver, which allows the driver to rest their legs on long trips.

Overdrive will not maintain speed. Its purpose is to reduce wear on the engine and save fuel while driving at higher speeds.

What are the benefits of using overdrive?

Overdrive can improve your fuel efficiency and reduce road noise while driving at steady highway speeds. In automatic cars, overdrive is on automatically, so it provides these benefits without input from the driver.

Does overdrive make your car faster or slower?

No, overdrive does not make your car go faster. It’s not like warp speed! Instead, overdrive allows your car to travel at a higher speed (the same speed) while reducing wear and tear on the engine.

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