What is the rear diff ratio of a Subaru Impreza?
The rear differential ratio is not fixed across all Impreza models. It varies by generation, trim, and transmission. In general, Subaru’s AWD Impreza models use final-drive ratios in roughly the 3.7:1 to 4.11:1 range, with exact numbers determined by year and configuration.
Understanding why this matters helps put the question in context: the final-drive ratio influences highway RPM, acceleration feel, and transmission calibration, and it can differ between base models, WRX variants, and CVT-equipped versions. Below, you’ll find a guide to what ranges are commonly seen and how to determine the exact figure for a specific car.
Common ranges seen in Impreza models
These figures are approximate and illustrative of typical configurations across generations. Exact ratios vary by market and year, so check your vehicle documentation for precision.
- 3.7:1
- 3.9:1
- 4.11:1
Note: The precise rear-axle ratio for any given Impreza should be confirmed on the vehicle itself or via official documentation, as trims and transmissions can shift the final-drive value within this general range.
How to find the exact rear diff ratio for your car
Use these steps to confirm the precise ratio for your specific Impreza model and year.
- Inspect the differential housing for a stamped or engraved ratio code (often something like "3.70" or "4.11").
- Consult the owner’s manual or the factory service manual, which lists the final-drive/rear axle ratio for each model/trim.
- Provide your VIN to a Subaru dealer or use Subaru’s official online service portal to decode the final-drive ratio.
- If you’re unsure, ask a qualified technician to verify via service documentation or by counting gear teeth on the ring gear and pinion (more involved and typically a mechanic’s task).
After confirming the exact ratio, you can use it for maintenance planning, tire size changes, or any transmission/differential work to ensure proper gearing and speedometer accuracy.
Why the rear diff ratio matters
The final-drive ratio affects engine RPM at highway speeds, acceleration feel, and the overall gearing of the car. A taller ratio (lower numerical value) reduces engine RPM at a given speed, improving highway fuel economy but potentially reducing off-the-line torque feel. A shorter ratio (higher numerical value) raises engine RPM for quicker off-the-line acceleration but can increase engine wear and reduce fuel economy at speed. For Impreza models, the ratio is chosen to balance AWD performance with typical usage patterns for each trim.
Bottom line
There isn’t a single, universal rear differential ratio for the Subaru Impreza. It varies by generation, trim, and transmission, with common values in the 3.7:1 to 4.11:1 range. To know your exact figure, check the differential tag, consult the vehicle manual or service documentation, or have a dealer decode the VIN. This ratio is essential for accurate speedometer readings and proper drivetrain behavior, especially if you’re changing tires, gears, or performing differential work.
Summary: The Impreza’s rear diff ratio is model- and year-specific, typically between 3.7:1 and 4.11:1. Verify your exact figure via the differential tag, official manuals, or a dealer using your VIN to ensure correct gearing and related maintenance decisions.
