Fourth Place: BMW X5 4.4i cont...
At the wet racetrack, we thought the X5 finally would leap out ahead of the much larger SRX, which had been nipping at its heels on every other test. The X5 made the circuit a second quicker than the SRX at 1:13. We found the X5 produced terminal understeer even under full throttle in a high-speed sweeping turn, where two of the others' AWD systems seemed to overcome this tendency.
BMW's new xDrive AWD system is a departure from last year's, which used a planetary center differential to permanently apportion front/rear torque at 38/62 percent.
Just for the record, we made laps in all four with their stability systems activated (and busy) to make sure we weren't unfairly disabling a system that might produce better lap times. It turned out all four made their quicker laps with the systems shut off.
The new multidisc-clutch transfer case continually interprets a multitude of dynamic data to vary the amount of power being routed to front or rear axles. In normal driving, the system operates on a 40-front/60-rear split, but it can make an even 50/50 or lopsided 0/100 front/rear split under certain circumstances. Unfortunately, one of the circumstances where the front wheels were effectively undriven was severe understeer as described above. This means that, even under full throttle in a fast corner, only the rear wheels were getting power, producing a bigger push. The solution was to gradually lift out of the gas until the front wheels bit and obeyed the steering input.
Certainly, the X5 is a beauty inside and out, and we can appreciate its flawless build, communicative driving dynamics, and strict adherence to BMW values. However, the X5 just can't run with this capable pack at the track.