2017 Tesla Model S Transmission & Axle Gear Ratios

When discussing powertrain specifications for the 2017 Tesla Model S, the conversation shifts radically from traditional internal combustion engine (ICE) vehicles. Unlike gas-powered cars that rely on multi-speed automatic or manual transmissions and selectable rear differential ratios, the Tesla Model S utilizes an advanced all-electric drivetrain featuring single-speed fixed-gear reduction units. While you won't find a traditional 6-speed or 8-speed gearbox under the floorboards, understanding the gear reduction in the front and rear drive units is essential for EV enthusiasts, technicians, and modifiers aiming to comprehend how the Model S delivers its blistering, seamless acceleration.

Whether you own a standard rear-wheel-drive Model S 75, a Dual Motor 90D, or the flagship Performance P100D, the gear ratios are fixed by the type of drive unit installed at the factory. Below is a comprehensive breakdown of the transmission and axle reduction ratios utilized in the 2017 Tesla Model S lineup.

Transmission gear ratios

The 2017 Tesla Model S does not have a traditional transmission with multiple forward gears. Instead, it utilizes a transaxle housing a single-speed fixed reduction gear. The electric motor spins at very high RPMs (up to 18,000 RPM), and this reduction gear steps down the motor's speed to an appropriate wheel speed while simultaneously multiplying torque.

Because the Model S reverses by simply spinning the electric motor in the opposite direction, the reverse gear ratio is identical to the forward gear ratio.

Large Drive Unit (Performance Rear Motor - e.g., P100D, P90D)

Small Drive Unit (Front Motor on AWD models & Base Rear Motor)

Available axle ratios

In a Tesla, the transmission's single-speed reduction gear essentially is the axle ratio (final drive ratio). There is no separate traditional ring and pinion differential in a solid axle. Instead, an open differential is integrated directly into the drive unit. Electronic traction control and independent motor control (in Dual Motor models) handle the torque vectoring rather than a mechanical limited-slip differential.

You cannot option different axle ratios from the factory like you can with a traditional truck or muscle car; the ratio is permanently tied to the specific drive unit architecture.

How to identify your axle ratio

Because electric vehicles do not utilize traditional axle housings or selectable rear-end gears, you won't find a standard door-jamb RPO sticker (like GM) or a metal differential cover tag (like Ford or Ram) to decipher your gear ratio. Instead, identifying your gear reduction ratio comes down to identifying which drive unit(s) your Tesla Model S is equipped with.

1. VIN Decoder: The easiest way to determine your powertrain configuration is to use a Tesla-specific VIN decoder. The 8th digit of your 2017 Model S VIN indicates the motor type (e.g., Single Motor, Dual Motor Standard, or Dual Motor Performance).
2. Vehicle Trim Badge: The badge on the rear trunk lid is a direct giveaway. A "P" (e.g., P100D) indicates a Large Drive Unit in the rear, which utilizes the 9.73:1 reduction gear. Standard "D" models (e.g., 90D, 100D) use the Small Drive Units front and rear with the 9.32:1 reduction gear.
3. Drive Unit Nameplate: If you are sourcing a salvaged part, each drive unit has a metal identification plate affixed to the inverter housing detailing the exact part number, which cross-references directly to its internal gear ratio.

Towing vs MPG impact

In the traditional automotive world, a numerically lower ratio (like 3.31:1) yields better fuel economy at highway speeds, while a numerically higher ratio (like 4.10:1) increases torque for towing and off-the-line acceleration but hurts MPG.

For the 2017 Tesla Model S, the concept is similar but applied to electric efficiency (MPGe and total range) rather than liquid fuel. The massive torque curve of electric motors negates the need for multiple gears. The engineers optimized the 9.32:1 and 9.73:1 ratios to provide a perfect middle ground: enough mechanical advantage to propel a 4,900+ lb sedan from 0 to 60 mph in under 3 seconds (in the case of the P100D), yet allowing the motor to spin efficiently enough at 70 mph to achieve over 300 miles of range. Towing is generally not recommended by Tesla for the 2017 Model S, but the torque multiplication from these steep reduction gears makes moving heavy loads effortless.

Common issues

While electric transaxles are generally simpler and more robust than traditional multi-speed automatic transmissions, the 2017 Model S drive units are not without their known issues:

• Milling/Whining Noise: Early to mid-production Tesla drive units (particularly the Large Rear Drive Units) are notorious for developing a high-pitched "milling" or circular saw-like whine under acceleration. This is often caused by premature wear on the rotor bearings or the main reduction gear bearings.
• Coolant Ingress: Internal seals can occasionally fail, allowing the dielectric fluid or battery coolant to bypass and enter the main rotor assembly, leading to drive unit failure and isolation faults.
• Differential Spline Wear: High mileage or frequently hard-launched vehicles may experience wear on the splines where the axle half-shafts meet the differential output. This results in a noticeable "clunk" when transitioning from regenerative braking to acceleration.

If your Model S is experiencing drive unit noises, fluid leaks, or acceleration clunks, it is highly recommended to have a specialist inspect the transaxle assembly before catastrophic failure occurs.

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