2018 Tesla Model X Transmission & Axle Gear Ratios

The 2018 Tesla Model X is a marvel of modern electric vehicle (EV) engineering, combining supercar-level acceleration with the practicality of a three-row SUV. Because it is a fully electric vehicle, its drivetrain operates fundamentally differently from traditional internal combustion engine (ICE) vehicles. You will not find a multi-speed automatic transmission or a heavy-duty solid rear axle with selectable ring and pinion gears. Instead, the Model X utilizes a direct-drive, single-speed reduction gear system for both the front and rear electric motors.

Understanding these fixed gear ratios is crucial for EV enthusiasts, technicians, and owners who want to fully grasp how the Model X delivers its signature instant torque and impressive towing capabilities. Here is your comprehensive guide to the 2018 Tesla Model X transmission and axle gear ratios.

Transmission gear ratios

Unlike traditional vehicles that require multiple gears (1st through 6th, 8th, or 10th) to keep an engine within its optimal power band, the electric motors in the 2018 Tesla Model X have a massive, flat torque curve. They can spin up to 18,000 RPM, meaning a single-speed reduction gear is all that is necessary to propel the vehicle from zero to its top speed. Reverse is achieved simply by spinning the electric motors in the opposite direction, rather than engaging a dedicated reverse gear.

The 2018 Model X was available in configurations such as the 75D, 100D, and P100D (Performance). All utilize a Dual Motor All-Wheel Drive setup, but the gear ratios differ slightly between the front and rear drive units to optimize efficiency and power delivery.

Front Drive Unit (All Trims)

Rear Drive Unit (75D & 100D)

Rear Drive Unit (P100D Performance)

Available axle ratios

In a conventional truck or SUV, the "axle ratio" refers to the ring and pinion gear inside the differential. Buyers often choose between ratios like 3.31, 3.73, or 4.10 depending on whether they prioritize towing power or highway fuel economy.

In the 2018 Tesla Model X, the single-speed reduction gear inside the drive unit acts as both the transmission and the axle ratio. There are no selectable axle ratios or mechanical limited-slip differentials to choose from; the vehicle uses open differentials and relies on highly advanced traction control (via individual brake application and motor modulation) to manage wheel slip.

How to identify your axle ratio

If you are accustomed to looking for a door-jamb RPO sticker on a GM vehicle or a metal axle tag bolted to the differential cover on a Ford or Ram, you will need to adjust your approach for a Tesla.

Because the gear ratios in the 2018 Model X are fixed based on the trim level, there are no specific axle codes to hunt down. To confirm what reduction gear your Model X has:

1. Check the Trim Badge: Look at the rear tailgate. If it says 75D or 100D, you have the standard 9.32:1 ratio front and rear. If it says P100D (often underlined to denote "Ludicrous" mode), you have the 9.32:1 front and 9.73:1 rear setup.
2. Use a VIN Decoder: Run your Vehicle Identification Number (VIN) through a Tesla-specific VIN decoder. This will confirm the exact battery pack and motor configuration built at the factory.
3. Inspect the Drive Unit Plate: If you have access to a lift, there is an identification plate affixed directly to the front and rear drive units that lists the motor type and part number, which dictates the internal reduction ratio.

Towing vs MPG (Range) impact

In traditional vehicles, a numerically higher gear ratio (e.g., 4.10) is better for towing but hurts MPG, while a lower ratio (e.g., 3.31) improves MPG but makes the vehicle sluggish under a load.

For the 2018 Model X, the fixed ~9.3:1 to 9.7:1 reduction ratios provide a massive mechanical advantage. When combined with the instant torque of the electric motors, this fixed setup allows the Model X to tow up to 5,000 pounds with incredible ease. However, towing with an EV heavily impacts your "MPGe" or electric range. Because electric motors are so efficient, the increased aerodynamic drag and weight of a trailer can cut your driving range by 40% to 50%. The gear ratio itself cannot be changed to mitigate this; the range loss is purely a function of physics and aerodynamics.

Common issues

While the reduction gears themselves are incredibly robust and rarely fail, the drivetrain of the 2018 Model X does have a few known issues that owners should be aware of:

• Half-Shaft Shudder: This is the most infamous issue with the Model X drivetrain. Hard acceleration, especially in a P100D with the air suspension set to "High" or "Very High," puts extreme angles on the front CV joints (half-shafts). Over time, this causes premature wear, resulting in a distinct shudder or vibration under acceleration. Tesla has issued updated half-shafts and mounts to help mitigate this.
• Drive Unit Milling Noise: A distinct hum or "milling" noise at highway speeds can indicate wear on the drive unit's internal bearings. If caught early, this can sometimes be repaired, but it often necessitates a drive unit replacement.
• Fluid Leaks: The drive units are cooled and lubricated by a specialized fluid. Though rare, seals can degrade, leading to fluid leaks that can ultimately starve the reduction gears and motor bearings of lubrication.

If your Model X is experiencing drivetrain shudder, odd humming noises, or suspension issues, it is highly recommended to have it inspected by a qualified professional. Find a driveline shop on Repairius to ensure your EV stays in top running condition.