2017 Subaru Legacy: Winning the Fuel Economy Challenge


Here’s the challenge for Subaru engineers: Start with the same formula for a sedan – a 2.5-liter SUBARU BOXER engine, automatic transmission, Symmetrical All-Wheel Drive (AWD) and all the latest safety and convenience features – but dramatically increase fuel economy. 

Over the past 10 years, the engineers for the Subaru Legacy have aced this challenge. EPA fuel economy estimates for the Legacy have increased by up to 32 percent1 – and that’s with more stringent test requirements for the 2017 model year.

This jump in efficiency is even more impressive when you consider that compared to the 2007 – 2009 Legacy, the 2017 model has more passenger room, trunk space and standard equipment. Even with today’s relatively low gas prices, trading in a 2009 Legacy on a similarly equipped 2017 model could save you more than $310 a year in fuel costs. Multiply that by years of ownership, and you’re talking real savings.

The nuts and bolts behind this accomplishment are a bit complex, but it’s easy to understand the basic concepts. So let’s dive in.

The Legacy is the longest-lasting midsize sedan in its class.2

2017 Subaru Legacy AWD 29 mpg combined city/highway
2012 Subaru Legacy AWD 26 mpg combined city/highway
2009 Subaru Legacy AWD 22 mpg combined city/highway
(Left) 2017 Subaru Legacy AWD 29 mpg combined city/highway. (Top Right) 2012 Subaru
Legacy AWD 26 mpg combined city/highway. (Bottom Right) 2009 Subaru Legacy AWD
22 mpg combined city/highway.

Gliding through the Air 

Let’s imagine paddling a boat through the water. It’s more difficult to push a flat-bottomed fishing boat through the water than a canoe, with its sleek shape. Just substitute air for water, and you have a basic understanding of aerodynamics.

Each new-generation Subaru model benefits from hundreds of hours dedicated to cutting air resistance. Engineers hone the shape of the car as well as tweak many details for this purpose alone, all in a quest to cut air resistance. That’s because the general rule of thumb for engineers is that for every 10 percent of reduction in aerodynamic drag, fuel consumption is potentially reduced by three percent. 

Take a good look at a new Legacy and you’ll notice that some of these aero features are obvious. 

Up front, where the air meets the grille, all Legacy 2.5i models have an Active Grille Shutter below the bumper. At low speeds, this shutter is open for extra engine cooling. But at highway speeds, it closes, reducing aerodynamic drag and helping to increase highway fuel efficiency.

All 2017 Legacy 2.5i models have an Active Grille Shutter below the bumper that opens and closes depending on speed.
All 2017 Legacy 2.5i models have an Active Grille Shutter below the bumper that opens and closes depending on speed.

The windshield is steeply raked to help air flow over the vehicle’s hood and onto the roof without encountering major resistance. The trunk lid of the Legacy has a subtle “lip spoiler” that helps reduce air turbulence at the rear of the car. The lower door sills are precisely shaped to smooth airflow along the sides. Even the design of the undercar panels is carefully considered in the quest to cut air drag.

Not only that, but all of these advancements have been done while designing the Legacy interior with one of the roomiest in its class. Now that’s an accomplishment.

The 2017 Legacy has a completely new engine series versus the engine in the 2009 model.
The 2017 Legacy has a completely new engine series versus the engine in the 2009 model.

A More Efficient Boxer 

The 2017 Legacy has a completely new engine series versus the engine in the 2009 model. The only thing the two engines share is the 2.5 liters of displacement.

From the shape of the pistons to the design of the fuel injection to the way the valves are controlled, the 2017 Legacy engine has been optimized in myriad ways to reduce fuel consumption. Each drop of gasoline that goes in does more work than it used to.

Some of these enhancements are the result of precision electronics, like the Electronic Throttle Control that works more efficiently than a mechanical system of cables and springs. The steering is now assisted with an electric motor instead of the traditional hydraulic pump, so that’s one less “accessory” for the engine to power.

Some of the efficiency gains are the result of cutting friction in the engine. The 0W-20 synthetic motor oil that’s used in the Legacy 2.5i is designed to not only help protect the engine under a wide range of driving conditions and temperatures, but it’s also slipperier, meaning the engine does not work as hard.

Are you detecting a theme here? Think of it this way: under the suit of clothes of a four-door sedan, the 2017 Legacy has finely-honed muscles that allow it to make effortless moves without breaking a sweat.

Subaru Symmetrical AWD powers all four wheels – all the time.
Subaru Symmetrical AWD powers all four wheels – all the time.

The Beauty of Symmetry

 Subaru Symmetrical AWD powers all four wheels – all the time. While the obvious benefits are traction and control, it does mean there are more drivetrain components compared to a front-wheel drive car. But the benefits of this Subaru design comes from the symmetrical layout. 

Picture a bird’s eye view of the Legacy, and draw a line from the middle of the front bumper across the hood, roof and trunk to the middle of the rear bumper. By dividing the car in half this way, you can see that the engine and drivetrain components are equally divided, right to left, creating ideal symmetry.

Most front-wheel drive cars use a transverse (sideways) engine and place the transmission on one side. When these cars are converted to AWD, engineers must design a variety of turns and angles in the drivetrain. Each of these 90-degree turns adds friction, which means the engine has to work harder to power the wheels – and that means using more fuel.

And here’s the best part: the Legacy 2.5i has higher EPA fuel economy estimates than some front-wheel drive cars! You get the benefits of AWD without sacrificing fuel economy.

Slowing Engine Speeds on the Highway 

If there’s one central hero in this Legacy fuel economy story, it’s the Subaru Lineartronic CVT (Continuously Variable Transmission). Not only does this innovative transmission deliver smooth acceleration, but it also helps reduce engine speed when cruising down the highway. 

All transmissions have multiple gear ratios to help the engine accelerate the car from rest, while also keeping engine speeds low on the highway. Some transmissions do a better job at this because the “spread” from the lowest gear ratio (for starting out) and the highest gear ratio (for cruising) is wide. For the Lineartronic CVT, this ratio spread is more than 6:1. 

Optimizing the Operating System 

All of these engineering features and high-efficiency design details rely on the human operating system behind the steering wheel – you. There are many factors that can significantly cut into your mpg:

  • Quick acceleration and heavy braking
  • Excessive idling
  • Frequent short trips
  • Improperly aligned or inflated tires

The best way for you to win the fuel economy challenge is to track your fuel mileage using the Legacy trip computer and ECO gauge, and regular vehicle maintenance.

After all, the Legacy was designed for efficiency. The rest is up to you!

1 EPA City, Highway and Combined fuel economy estimates for 2007-2009 Subaru Legacy 2.5i with automatic transmission compared to the 2017 Legacy 2.5i with Lineartronic CVT. Actual mileage may vary. 2 Based on IHS Automotive, Polk U.S. total new light vehicle registrations in the model years 2005 through 2015 (through December 2015) in the Non-Luxury Traditional Midsize Sedan segment for models that have been on the U.S. market for the entire ten-year time period.

2017 Legacy