2018 Subaru Outback Transmission and Axle Gear Ratios

When delving into the nuances of a vehicle's performance and efficiency, understanding the transmission and axle gear ratios is paramount. For the 2018 Subaru Outback, these ratios play a significant role in its all-wheel-drive capabilities, fuel economy, and overall driving dynamics.

Transmission gear ratios

The 2018 Subaru Outback was exclusively offered with a continuously variable transmission (CVT), which Subaru markets as Lineartronic. This transmission is designed to provide seamless acceleration and optimal fuel efficiency by constantly adjusting the gear ratio.

Lineartronic CVT (TR580 - 2.5i models, TR690 - 3.6R models)

Note: The CVT does not have discrete gear ratios in the traditional sense, but rather a continuous range. The values provided represent the lowest and highest ratios it can achieve.

Available axle ratios

The final drive ratio, often referred to as the axle ratio, is crucial for determining how engine power is translated to the wheels. For the 2018 Subaru Outback, the axle ratios vary depending on the engine and transmission combination.

How to identify your axle ratio

Unlike some other manufacturers, Subaru typically does not use an easily identifiable RPO code sticker on the door jamb for the axle ratio. Instead, the axle ratio is generally tied directly to the engine and transmission combination.

• For 2.5L models: The vast majority of 2018 Subaru Outbacks with the 2.5L four-cylinder engine will have a 3.900 final drive ratio.
• For 3.6L models: All 2018 Subaru Outbacks equipped with the 3.6L six-cylinder engine will have a 3.700 final drive ratio.

If you need absolute confirmation, the most reliable method is to check the build sheet or the vehicle's VIN decoder information, often available through a Subaru dealership or online VIN decoding services. In some cases, the ratio might be stamped on the differential housing itself, but this often requires getting under the vehicle and is less convenient.

Towing vs MPG impact

The interplay between axle ratio, towing capacity, and fuel economy is a critical consideration for any vehicle owner. For the 2018 Subaru Outback, a few general principles apply:

• Numerically Lower Ratio (e.g., 3.700 on 3.6R): While 3.700 is numerically lower than 3.900, in the context of the engines, the 3.700 ratio paired with the more powerful 3.6L engine is designed to handle more demanding situations like towing. Generally, a numerically lower axle ratio means the engine turns fewer revolutions per minute (RPM) for a given road speed. This typically translates to better fuel economy on the highway as the engine is working less. However, it can also mean less torque multiplication at the wheels, potentially making the vehicle feel less responsive from a standstill or when towing heavy loads.

• Numerically Higher Ratio (e.g., 3.900 on 2.5i): A numerically higher axle ratio means the engine turns more RPMs for a given road speed. This provides greater torque multiplication, resulting in quicker acceleration and enhanced towing capability for that specific engine. While it aids in getting heavier loads moving and provides more immediate power, it can also lead to slightly lower fuel economy, especially at higher speeds, as the engine is constantly working at a higher RPM.

For the 2018 Outback, the 3.900 ratio with the 2.5L engine strikes a good balance for daily driving and light towing, optimizing fuel efficiency. The 3.700 ratio with the 3.6L engine, despite being numerically lower, is paired with a more powerful engine and is better suited for those who prioritize performance and the higher end of the Outback's towing capacity (when properly equipped).

Common issues

Subaru's drivetrains are generally reliable, but like any mechanical system, they can experience issues. Specific to gear ratios and differentials, some occasional issues reported across various Subaru models (not necessarily exclusive to the 2018 Outback) can include:

• Rear Differential Whine: This is often noticed as a humming or whining sound that increases with vehicle speed. It can be caused by worn bearings within the differential or improper mesh of the ring and pinion gears. While not always a sign of imminent failure, it warrants investigation.
• CVT Longevity Concerns: While not directly a "gear ratio" issue, some owners of Subarus with CVTs have reported concerns about the long-term durability of the transmission. Regular maintenance, including fluid changes at recommended intervals, is crucial for CVT health.

It is important to remember that these are general observations and not necessarily widespread problems with the 2018 Outback. Regular maintenance and addressing any unusual noises promptly can prevent minor issues from becoming major repairs.

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