2016 Tesla Model S Transmission & Axle Gear Ratios

The 2016 Tesla Model S is a marvel of modern electric vehicle (EV) engineering, delivering instant torque and blistering acceleration without the need for a traditional internal combustion engine. Because it is a battery-electric vehicle, the Model S fundamentally differs from conventional gas-powered cars when it comes to driveline mechanics. Instead of multi-speed automatic or manual transmissions and selectable rear differential ratios, the Model S utilizes a single-speed fixed reduction gear system integrated directly into the electric drive units.

If you are transitioning from the world of internal combustion or simply want to understand the mechanical reduction inside your 2016 Tesla Model S, this guide breaks down the transmission and final drive "axle" ratios for this groundbreaking EV.

Transmission gear ratios

Unlike standard vehicles that shift through multiple gears (1st through 6th, 8th, or 10th) to keep the engine in its optimal power band, electric motors boast a massive, flat torque curve that reaches up to maximum RPM. As a result, the 2016 Tesla Model S uses a single-speed gearbox. There is no reverse gear; the vehicle simply spins the electric motor in the opposite direction to back up.

Tesla utilizes two primary drive units for the 2016 model year: the Large Drive Unit (LDU), typically found on the rear axle of Performance models (like the P90D or P100D) and older RWD models, and the Small Drive Unit (SDU), used on the front axle of Dual Motor (AWD) cars and the rear axle of standard non-performance Dual Motor trims.

Large Drive Unit (LDU) Single-Speed Gearbox

Small Drive Unit (SDU) Single-Speed Gearbox

Available axle ratios

Because the reduction gear is built directly into the drive unit as a transaxle assembly, the "axle ratio" is identical to the transmission gear ratio. There are no optional ratios (like 3.55, 3.73, or 4.10) to select when purchasing the vehicle; the ratio is permanently dictated by the drive unit equipped on your specific trim.

Note: In Dual Motor configurations (e.g., 90D, P90D), the vehicle utilizes software to blend the power seamlessly between the front SDU (9.34:1) and the rear drive unit (either 9.34:1 or 9.73:1, depending on standard or Performance trim).

How to identify your axle ratio

In traditional domestic trucks and SUVs, you might look at a door-jamb RPO sticker (for GM) or a metal axle tag (for Ford/Ram) to find a three-digit alphanumeric code.

For the 2016 Tesla Model S, the process is slightly different:

1. VIN Decoder: The easiest way to verify your drive unit configuration is by decoding the Vehicle Identification Number (VIN). The 8th digit of a Tesla VIN denotes the motor type (e.g., Single Motor, Dual Motor, Performance Dual Motor).
2. Drive Unit Tag: If the vehicle is safely lifted, you can inspect the physical data plates riveted or stickered onto the drive units themselves. A part number indicating a Large Drive Unit confirms the 9.73:1 ratio, while a Small Drive Unit indicates a 9.34:1 ratio.
3. Vehicle Software: Tapping the Tesla "T" or the "Software" tab on the central MCU screen will show exactly what trim you have (e.g., 75D, 90D, P90D), which dictates your factory drive units.

Towing vs MPG impact

In the internal combustion world, a numerically lower ratio (e.g., 3.31) provides better MPG, while a higher ratio (e.g., 4.10) provides better towing capacity.

In the 2016 Tesla Model S, the fixed 9.x:1 ratios are specifically engineered to balance low-end torque for launching the heavy vehicle and high-end rotational speeds for highway cruising.

• Fuel Economy (Range): The 9.34:1 ratio on the Small Drive Unit allows the motor to spin slightly slower at highway speeds, contributing to the excellent highway range of non-performance "D" models.
• Towing: The Model S is not officially rated for towing by Tesla. However, the immense torque multiplied by the steep 9.73:1 ratio of the Large Drive Unit gives it massive pulling power, though doing so drastically depletes battery range (often by 50% or more) due to aerodynamic drag and weight.

Common issues

While electric transaxles have far fewer moving parts than a traditional multi-speed automatic, they are not immune to issues.

• Milling Noise (Large Drive Unit): Early and mid-production Large Drive Units are known to develop a high-pitched "milling" or humming sound under acceleration. This is often caused by bearing wear inside the motor or the reduction gear housing.
• Coolant Leaks into the Rotor: Internal seals can occasionally fail, allowing stator cooling fluid to leak into the rotor cavity, which can lead to drive unit failure and necessitates replacement.
• CV Joint and Half-Shaft Wear: Because of the instant torque delivered by the 9.x:1 gear reduction, the inner CV joints and half-shafts can wear out prematurely, particularly on Performance models subject to frequent hard launches.

If your EV is experiencing driveline humming, clunking, or warnings on the dash, it requires specialized care. Find a driveline shop on Repairius to get expert diagnostics and drive unit servicing.