BMW also fits the M3 and M4 with its M Dynamic Modes

Managing the power at the rear is a new Active M Differential, an electronically controlled, multi-plate setup that's a degree more sophisticated than a mechanical limited-slip unit. BMW also fits the M3 and M4 with its M Dynamic Modes, that offer tailoring for the stability control system--even turning the stability and traction control systems off completely.

The suspension teams the usual front struts and multi-link rear, with more aluminum used to reduce unsprung weight. You can add it right back in with the optional Adaptive M suspension which gives direct control over Efficiency, Comfort, and Sport settings. And on the controversial end, the M cars have electric power steering that BMW says has been designed and built with the track in mind. It too has three driver-selectable modes: Comfort, Sport, and Sport+. Carbon-ceramic brakes are an option, and Michelin Pilot Super Sport tires are standard. All the driving modes can be programmed into the M1 and M2 buttons on the steering wheel, just a tap away when you're driving.

Unlike some other pony cars we could name--let's be real, the M4 has essentially evolved into maybe the world's best Mustang--the BMW actually makes concessions at losing weight. It's down about 176 pounds to just below 3,300 pounds for the coupe, according to BMW, via an aluminum hood and front fenders, a carbon-fiber driveshaft and strut braces, less sound insulation, a composite decklid, and selective deletions like the seat-belt presenter found on 3-Series and 4-Series, non-M cars. Maybe 176 pounds isn't a huge amount, objectively, but the Bimmers are marginally larger than before--and there's more weight to be saved with the carbon-fiber reinforced-plastic roof (11 pounds lighters on the sedan, 13 on the coupe).

The weight loss works with aerodynamic tweaking around those massive front ducts and hulking wheel wells. And to keep the M3 and M4 bubbling, not boiling over, on the track, there's a track-intent cooling circuit for the engine, turbos, and transmission. Even the intercooler gets its own coolant pump.

What happens when driver inputs filter through a stronger and somewhat lighter body, via BMW's home-wired neurotransmitters, to some of the most challenging pavement we as Americans can throw at it?