The xDrive system has two primary purposes. First, it improves safety by maximizing a vehicle's traction on the road. Secondly, it enhances driving dynamics and stability in curves.
The xDrive system is active all the time but only steps in when it detects a potential hazard due to low grip and uneven surfaces or a sharp change in direction. The system optimizes traction, improves agility, and works to keep a vehicle safely in its lane. It operates almost instantaneously when needed and in a manner that goes virtually unnoticed by the driver.
From a traction standpoint, the xDrive system is geared toward those who live in colder climates where snow, ice, and wintry conditions can cause wheel slippage or skidding and make driving unsafe. But it is equally valuable in wet and rainy conditions as well as off-road driving, where loose dirt and mud can result in the loss of traction.
The xDrive system permanently monitors the speed of each wheel. It can send up to 100 percent engine power to one axle, allowing the driver to gain traction quickly. Furthermore, it can direct all energy to the wheel(s) with the greatest traction, even if that means it's just one out of the four.
Under normal circumstances, xDrive distributes power between the front and rear axles in a 45-55 front-to-rear ratio. This ratio changes continuously in real-time driving at variable levels—from 50-50 to 0-100—depending on when road surface conditions change.
The system splits power between the axles using an electronically controlled multi-plate clutch located between the gearbox and the driveshaft. This configuration allows xDrive the flexibility to divide power between the axles and wheels in virtually any way it needs to maximize traction. Unlike many AWD systems, xDrive does not utilize a center differential.
Besides wheel speed, the system measures other factors such as the angle of the steering wheel, brake force, and pressure on the gas pedal. The system then employs these combined data points to ensure that the vehicle reacts in a given situation in the best possible way.
Aside from elevating safety in low-traction situations, the xDrive system inspires confidence during spirited driving, especially around curves at higher speeds. The system aims to bring every possible horsepower to the road's surface without wasting any energy to regain traction.
When driving through a curve, the xDrive system reduces the power to the inner curve wheels. This action supports the sideways motion of the vehicle and helps the driver exit the turn faster.
When a driver enters a curve with too much power going to the drive wheels, there may be a risk of oversteering or understeering. In this situation, the xDrive system shifts the power to the front or rear axle, depending on the needs.
At the first sign of understeering, drive power to the front axle is reduced. If oversteering is detected, xDrive directs more power to the front axle. Because of this dynamic redistribution of power, vehicle stability returns to normal before the driver notices an adjustment has even occurred.
The xDrive system works in tandem with Dynamic Stability Control (DSC) and uses information from the system's wheel-speed sensors to monitor road conditions. In addition, the system applies brake force when there is a traction difference between the two sides of the vehicle and wheel spin is imminent.
All these functions, together, allow xDrive to deliver maximum enjoyment in performance driving.
It takes more energy to drive four wheels than it does to drive two wheels. Plus, AWD systems bring more weight to a vehicle. These two factors will always equate to a reduction in fuel economy.
However, BMW has improved the xDrive system over the years to maximize efficiency. One way the automaker has accomplished this is to design the system only to transfer the amount of power to the respective axle that it can actually pass on to the road. This design eliminates the transference of any excess energy that would otherwise go to waste.
Whether you need AWD for wintry weather, trail riding, or zipping through curves, BMW has the answer. The xDrive AWD system offers impressive performance and the required surefootedness for both on-pavement and off-road driving.