First Drive: 2011 BMW X3 Prototype

Don Sherman
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When the crunch of CAFE regulations arrives in a few years, BMW will likely add both a turbo-diesel and a four-cylinder gasoline engine to the X3's powertrain menu.

While the current X3 is one of the few crossovers offered with a manual transmission, its replacement will drop the stick shift option. BMW cites a low take rate and certification costs as the obvious reasons. Between both of the available six-cylinder engines and the drive wheels, there's a smooth shifting and fuel economy boosting 8-speed ZF automatic transmission with a handy manual-mode and optional paddle shifting. Unfortunately, this transmission is programmed to deliver an automatic upshift at the redline in its manual-shift mode.

The standard on-demand all-wheel drive system, still called Xdrive, is shared with the big brother X5. Power to the rear axle is provided by a permanently engaged mechanical connection. A computer controlled multiplate clutch routes a measured amount of torque to the front axle. In normal driving the torque split starts at 40:60 f:r with adjustments as needed to maintain forward momentum in slippery or aggressive cornering conditions. To help the open front and rear differentials keep the wheels turning and to minimize understeer, the Dynamic Stability Control system has the authority to momentarily apply the brakes at any wheel and to automatically open the throttle to send extra torque to the outside rear wheel.

CHASSIS FINESSE WORTHY OF A BMW BADGE
The X3's suspension hardware is an offshoot of the equipment that underpins mainstream 3-series models. At the front there's a double-ball-jointed strut-type suspension with coil springs. The rear axle is a coil-sprung multilink arrangement similar to the suspension fitted to 3-series sedans equipped with Xdrive. Substantial front and rear anti-roll bars are included to deal with the X3's elevated center of gravity. Run-flat radials are standard equipment in 17-, 18-, and 19-inch sizes. No less than three different electrically assisted steering systems will be offered: a base system, a Servotronic speed-sensitive upgrade, and a sport steering option with ratios that vary according to wheel position instead of road speed. In every case, the electric assist motor is geared to the steering rack rather than to the pinion shaft to optimize the amount of road feel delivered to the steering wheel.

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