Power comes from a silky 4.4L twin-turbo V8 that makes 523 horsepower and 553 pound-feet of torque between 1,800 and 4,400 rpm. More importantly, when the top is down it sings a glorious song through the quad pipes — the crackling pops during overrun in Sport mode is sublime.
Of course, the real sweetness is found in the numbers. The wide, meaty torque plateau means the M850i responds instantly to a healthy stab at the gas. It runs from rest to 100 kilometres an hour in a tick under four seconds. That’s good, but it really catches fire through the mid-range — the 80-120 km/h passing move comes in at 2.8 seconds!
The M850i fairs equally well in terms of the manner in which it blends ride comfort with cornering ability. It starts with the adaptive suspension and runs through the M Sport rear differential and active steering. At low speeds, the rear wheels turn in the opposite direction to the front wheels, which shortens the turning circle and eases the parking chore. When the speeds are elevated, the rear steer points the wheels in the same direction as the front wheels. This improves the response to input and adds to the sense of stability. It also helps to mask the M850i’s full-bodied size — it is a big car, but it has a mid-sized feel to the way it dives into a corner.
What separates the good from the bad in the convertible world is cowl shake. The easiest way of understanding this phenomenon is to look at a shoe box. With the lid in place the box has surprising torsional strength; take the lid off and it has the structural integrity of a soggy noodle. So it is with a car. Removing the second largest panel hurts the structural integrity. Yes, extra bracing and structural supports help replace the strength, but if it’s not done properly the body shakes and shimmies like a crazed go-go dancer when running a rutted corner. In this case, cowl shake in a non-issue. The result is a drive that has grand touring comfort about town, yet on a twisty backroad it’s nimble when heading into a corner and planted as it hauls out after clipping the apex.
Where things do get complicated is the drive modes. There are Eco Pro, Comfort, Sport and Adaptive, but within each there are choices. For example, in Sport there are Standard and Plus settings along with an individual mode that allows the driver to tweak the suspension, steering, engine and transmission separately. Frankly, adopting a back-to-basics approach would suffice — Comfort for the city and Sport Plus for the fun times.
The BMW M850i xDrive has a sharp style and it’s very quick, but, more importantly, it manages to blur the line between a grand touring convertible and a drop-top sports car. It is a boulevardier when out for a sedate evening cruise; ramp everything up to hyper and its M side really shines brightly.
