The X in the BMW 325xi

The BMW 325xi E46 has three differentials: one in the front, one in the middle and another one in the back.

The middle differential transfers power at a 32%/68% ratio favoring the back. This distribution, while providing a good grip to the car in wet conditions, favors the sporty driving experience in dry conditions by transferring more power to the back wheels.

The ratio is fixed mechanically and cannot be changed electronically like in other cars like Subaru or Saab.

The differentials are open and therefore do not have a Limited Slip Differential (LSD) mechanism. However the ADB-X (Active Differential Breaking) and DSC-X (Dynamic Stability Control) system, will enhance the grip of the vehicle by applying brakes and cutting off power to the wheels which are spinning. This system is controlled electronically via the central computer vs. the mechanical nature of LSD. It intervenes on each wheel individually to retain traction and is unoticeable to the driver.

The added AWD mechanism comes with a price. More than 100kg of weight which will make the vehicle stopping distance longer. However, it will make it start faster in normal conditions or get you off the snow in extreme weather.

The E90 models are fitted with the xDrive system, which is a bit more elaborated and designed to distribute the torque based on the road conditions.

To Disable DSC-X: Press the button once. To Disable ADB-X: Keep holding the button won't work on the 325 xit model, it is only supported on the non-X E46.