The i8 isn’t the first carbon-fiber-intensive car. But along with its cousin, the i3, the i8 is the clearest indication yet that the future belongs to cars made from material that’s ultrastrong yet weighs half as much as steel.

Whereas the US $42,300 i3 is a toaster-shaped urban runabout, the i8 is a two-plus-two sports car that can sip fuel, cruise on electricity for short hops, or scorch the asphalt anytime you like. Channeling the spirit of Messrs. Jekyll and Hyde, I took test drives in New York and the Midwest, including thrilling laps at GingerMan Raceway, in western Michigan.

The carbon-fiber passenger cell of an i8, its technical heart, is molded in a patented process that takes minutes rather than the hundreds of hours needed to handcraft the material in recent supercars that cost $1 million. A 7.1-kilowatt-hour lithium-ion battery pack nestles below the floor. A 96-kW (129-horsepower) electric motor drives the front wheels through a full automatic two-speed transmission. The rear wheels get their urge from a 1.5-liter three-cylinder gasoline engine borrowed from BMW’s Mini Cooper but turbocharged to 170 kW (228 hp). Drivers manage the combined 266 kW (357 hp) and 569 newton meters (420 foot-pounds) of torque through a superlative six-speed, paddle-shifted automatic transmission.

Toggle up the console’s eDrive mode and the BMW will cover up to 35 km entirely on front-drive electricity, albeit at a leisurely 9.5-second pace to 100 km/h and a 120 km/h top speed. But cleverly, those 35 km don’t have to tick off sequentially the instant you unplug from a wall charger. The all-wheel-drive Sport mode replenishes the battery on the fly, adding about 1 km of pure electric-vehicle range for every 17 km driven. That feature enables drivers to preserve or add electric miles for urban use. A few cities, notably London, charge hefty entry fees for internal-combustion vehicles—and may eventually ban them outright.

Traveling up New York’s Hudson River, I spent some hours in the BMW’s Comfort mode, which maximizes electric efficiency but will seamlessly blend in gasoline power when you goose the throttle. Here, gentle highway driving produced a knockout 6.2 liters per 100 km (38 miles per gallon), roughly twice the efficiency of a similarly sized luxury GT, the Aston Martin DB9. Credit in part the BMW’s svelte 1,567-kilogram (3,455-pound) curb weight, some 220 fewer kilograms than the aluminum-chassis Aston and 540 fewer than the battery-stuffed Tesla Model S sedan. Overall, the BMW showed me 7.6 L/100 km (31 mpg) over several hard-driving days. That’s 3 mpg better than the car’s U.S. federal estimate and about 50 percent better than that of the latest Corvette Z06 or Porsche 911.

Solid-citizen duties complete, it was time for some fun. Tromp the i8’s throttle and you’re whisked into motion like protons in a collider. The instant signature shove of electric torque helps. The miniature gas engine chimes in with a backup duet voice. It’s canned but uncanny: a synthesized simulation of engine sound piped through door speakers to complement the actual exhaust note. You’d never know that a three-cylinder engine was at work; instead, the BMW’s chesty rumble sounds like a Porsche flat-six mating with a flying saucer.

Admiring that performance is easy, but admiring the electric motor is hard: As with the iPhone, another lowercase techno marvel, the i8’s hood is sealed, as it’s meant to be opened only by certified technicians. Other drawbacks include a toddler-size backseat and stingy storage.

But blasting down the road, bypassing the gas stations, you really won’t care. The i8 might have ended up as another Fisker Karma, a poorly integrated stew of hybrid technology. Instead, the BMW is real, and it’s here. Just in time for the future.