BMW electrifies its X5 SAV

When is a transmission not just a box of gears? When it’s the 8P75XPH, a brand-new device — and concept — from ZF, the German supplier of automatic transmissions to many high-end cars. Not only does it offer eight speeds ahead and one in reverse, it also tucks a powerful electric motor inside its housing, where it can help out a vehicle’s gasoline engine right at the source, as it were.

This unique package is barely larger than a normal transmission, which means Mr. Carmaker has only to figure out where to hide the electric batteries. In its new X5 xDrive40e plug-in hybrid SAV, sport activity vehicle, which is so equipped, BMW has put the high-voltage lithium-ion battery pack in the back, beneath the cargo bay floor.

Converting a large internal-combustion rig into a “green machine” isn’t that simple.

The engineers also have to coordinate the work of the two engines, gas and electric, and figure out how to recharge that battery pack and deal with the extra weight of all this new hardware. The plug-and-play X5 weighs 5,220 pounds, almost a quarter of a ton more than a gas-only six-cylinder X5.

That’s significant, but in BMW fashion the mass seems to have disappeared. Its clumsy name aside, the X5 xDrive40e is light on its feet — agile, responsive and fast — and shows no regenerative-braking drag.

It is also fiendishly complicated. Like all high-end German cars, seemingly everything in the X5-e is endlessly adjustable. But many people thrive on complexity — wristwatches bristling with buttons and subdials, and smartphone apps out the wazoo — so I’ll just have to get over it.

From the outside, the only clue to the vehicle’s electrified nature is what looks like a second gas-filler cap, on the left front fender. Open it and insert the supplied plug. Normal household current takes overnight to refill the 9.2-kilowatt-hour battery after a deep discharge; with 240-volt current, it can be done in about two hours. (The light-emitting-diode ring around the port pulses blue-green until charging is complete.)

Then the X5-e is good to go, with 111 horsepower and 184 pound-feet of torque from the electric motor plus 240 horsepower and 260 pound-feet from the turbocharged, 2.0-liter four-cylinder gas engine. BMW says this is good for a zero-to-60 mph dash in 6.5 seconds, but the X5-e feels quicker than that. And the system never lets the battery go flat entirely, so that substantial electric boost is always instantly available.

The X5-e is limited to 130 miles per hour, and BMW says it can hit 75 mph on volts alone. That may be, but not in 45-degree “spring” weather; no matter what buttons we pushed, the gas motor lit up as we reached about 60 mph. That’s hardly a deal-breaker — this is not an electric-only Tesla, after all — and the transition to internal combustion is largely transparent.

What you think is the engine starting is the transmission shifting down under load. The best indication that the electrics need help is that the tachometer dial suddenly wakes up. Until then, it’s slightly eerie to ghost around town with the engine-rpm needle flat-lined on zero and no noise save for tire hiss. Sneaking up on crosswalks can be fun.

Overall, we got an indicated 23 miles per gallon. BMW claims 24 mph in combined highway/city driving on gasoline alone and 56 miles per gallon equivalent on electricity + gas — in stop-and-go city traffic, say. (According to Consumer Reports, the most fuel-efficient sport utility vehicle is the Toyota RAV4 Hybrid, at 31 mpg overall.)

This is transitional technology, and the efficiency will improve as the X5-e cross-pollinates with its i3 and i8 electric cousins and the also-new 330e. The point is that (with ZF’s help) BMW is greening up one of its largest, heaviest and most popular cars.

Driving the X5 xDrive40e also is satisfying and rewarding, and — at $75,000 as equipped, or about $5,000 more than an X5 xDrive35i — ours is appropriately luxurious and safety-equipped, too. Is the X5-e a car or a statement? I’d have to live with it longer to say for sure.

But I’d look forward to doing so. Maybe that answers the question.