2015 Tesla Model S Transmission & Axle Gear Ratios

Transmission gear ratios

The 2015 Tesla Model S, being an electric vehicle, does not have a multi-speed transmission like internal combustion engine (ICE) vehicles. Instead, it utilizes a single-speed direct-drive transmission. This design simplifies the drivetrain, improves efficiency, and provides instant torque delivery.

This single gear ratio is optimized to provide a balance of acceleration and top speed suitable for the Model S's performance characteristics.

Available axle ratios

The Tesla Model S also deviates from traditional ICE vehicles in its axle ratio configuration. Each drive unit (front and/or rear) integrates the electric motor, power electronics, and a single-speed gearbox (which acts as the differential and final drive). Therefore, the "axle ratio" effectively refers to the final drive ratio within these integrated units and is consistent across most variants for a given year.

How to identify your axle ratio

For a 2015 Tesla Model S, identifying the "axle ratio" is straightforward as it's a fixed 9.73:1 for all models due to the integrated drive unit design. Unlike traditional vehicles with separate axles and differentials, there isn't a unique RPO sticker code or an axle tag to look for in the conventional sense. The information is inherent to the vehicle's design. If you need to confirm this for your specific vehicle, the best source would be the owner's manual or Tesla's service documentation, which will detail the specifications of the drive unit.

Towing vs MPG impact

For electric vehicles like the 2015 Tesla Model S, the concept of "MPG" (miles per gallon) is replaced by "MPGe" (miles per gallon equivalent) or simply Wh/mi (Watt-hours per mile) or range in miles. The single, fixed gear ratio of 9.73:1 is a direct consequence of the electric motor's broad and flat torque curve, which eliminates the need for multiple gears to keep the engine in its optimal power band.

While a numerically lower axle ratio in an ICE vehicle typically translates to better fuel economy (lower RPMs at highway speeds), and a higher ratio means better towing (more torque multiplication), this dynamic is different for EVs. The fixed 9.73:1 ratio in the Model S is a compromise designed to offer vigorous acceleration and a respectable top speed without sacrificing too much efficiency. Any significant towing with a Tesla Model S is generally not recommended nor supported by Tesla, as it is not designed as a primary towing vehicle. The primary focus is on maximizing range and performance.

Common issues

While the integrated drive units in the Tesla Model S are generally robust, some issues can arise, though they are not directly related to varying "axle ratios" as in traditional vehicles:

• Drive Unit Whine/Hum: Some owners report a noticeable whine or hum from the drive units, particularly at certain speeds or under specific loads. This can be due to manufacturing tolerances, bearing wear, or gear wear within the integrated gearbox.
• Bearing Wear: The bearings within the drive unit can wear over time, leading to increased noise or, in rare cases, play in the drivetrain. This is a common wear item in any rotating machinery.
• Motor/Inverter Issues: Although less common and not directly an "axle" issue, problems with the electric motor or its associated inverter can manifest as drivetrain issues, impacting performance or generating unusual noises.

These issues typically require diagnosis and repair by a certified Tesla service center or an EV specialist, as the drive units are complex, sealed assemblies.

Find a driveline shop on Repairius.