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BMW's i8, which will go on sale late next spring, was designed from a clean sheet of paper to be the company's first plug-in hybrid. Its mission is to deliver equal measures of performance and efficiency, using unusual and unexpected technology and materials to do so. So, with us only just getting behind the wheel of a prototype for the first time, we felt compelled to share 10 things you need to know about BMW's all-new i8. 1. The Most Power per Liter of Any BMW Engine Although the i8's internal-combustion engine only has three cylinders and displaces a mere 1499 cc, it develops 228 horsepower, or 152 horses per liter. That's more than any other engine in the BMW lineup, including the various M models. Credit goes to a largish turbo with 25 psi of boost, as well as to the various efficiency and combustion improvements in BMW's newest engine family. 2. An Electric Motor with a Transmission All electric cars have a gear reduction between the electric motor and the driveline, but the i8 is the only one with a two-speed transmission. The lower gear, with an 11 to 1 ratio, provides plenty of torque multiplication when the car is in the all-electric mode, which is limited to 75 mph. However, the i8 has a top speed of 155 mph and when you shift into Sport mode, the electric motor's transmission shifts into its higher gear, with a 6 to 1 ratio, so that the motor can provide useful thrust above 75 mph.  Directing power from the 129-hp electric motor to the front wheels is a two-speed automatic transmission. 3. Not Much of a Back Seat At first glance, the i8 looks as if it might have the accommodation of the slightly shorter and narrower 4-series, but in fact, the space in its cabin is more like a Porsche 911's. There's plenty of room in front, but the back seat is woefully shy on headroom and legroom. Moreover, the rear seatback is very upright and unless the front seats are fully raised, you won't be getting your feet under them. We find it better to fold the seatbacks and use that space to supplement the modest, five-cubic-foot trunk. That's the price for packing two powertrains into one car. 4. Carbon Fiber with a New Look The i8 makes good use of the excellent strength-to-weight properties of carbon fiber. But if you were expecting to see precisely and artistically arrayed sheets of woven CF cloth under a high-gloss clear coat, you'll be disappointed. That's because BMW has pioneered a new way of molding carbon-fiber panels that's faster and cheaper than traditional hand-laid autoclave methods. The i8's CF pieces have a matte finish with a less-obvious weave and a subtle checkerboard pattern, much like ripstop nylon. They're not as sexy, but they allow the use of carbon fiber at a lower price than ever before.  BMW's carbon-fiber-reinforced plastic looks a little different from the traditional carbon weave we've grown to love. 5. Is the i8 FWD, RWD, or AWD? In fact, the i8 is all of the above. When running in purely electric mode, it's a front-driver, because the electric motor is connected only to the front wheels. On the other hand, the gasoline engine, mounted transversely behind the cabin, is connected only to the rear wheels, so when it is providing the motivation, then the i8 is rear-drive. Of course, during many modes, including maximum acceleration, both powerplants are operating and all four wheels are driven. 6. Pay Close Attention to the i8's Tires Though positioned as a sports car, efficiency was a key goal of the i8. As a result, it comes standard with narrow tires that are optimized more for low rolling resistance than for high traction. Although 20 inches in diameter, they measure a mere 195/50 in front and 215/45 in the rear—on 7.0- and 7.5-inch-wide wheels. Optional 215/45 and 245/40 Bridgestone Potenza S001s on slightly wider wheels greatly enhance the grip and even stickier tires might be offered. Just make sure you don't get the base tires unless you value mpg more than cornering mph.  The optional 245/40 rear tires are considerably narrower than we'd like. 7. There are Actually Two Electric Motors Although the i8 specs describe only one 129-hp electric motor powering the front wheels, there's actually a second motor that occasionally provides propulsion. It's a 280-volt motor/generator connected to the gasoline engine with a belt drive. Developing up to 20 horsepower and 74 lb-ft of torque, this motor is used primarily to start the engine and to generate electricity to partially charge the battery in Sport mode. However, it can also provide a burst of torque when the gasoline engine experiences turbo lag at low rpm. The improved "throttle" response, helps the three-cylinder better keep up with the instantly responsive electric motor. During maximum acceleration, it also provides a bit of extra torque to make the most of the available traction. 8. What Material Is Used in Both the i8 and Smart Phones? Chemically-hardened glass, also known as Gorilla Glass, is used on the faceplate of most smart phones because it is tough even when it's thin. For those same reasons, it's used in the noise-attenuating bulkhead between the i8's passenger and rear-engine compartments. The window uses two layers of glass sandwiching a sheet of transparent acoustic-damping plastic. To keep the panel light—to minimize both vehicle weight and help lower the center of gravity—the glass sheets are only 0.7 mm—less than a 32nd of an inch—thick. Even a minor impact would fracture regular glass that thin, but the Gorilla Glass should survive nicely.
9. BMW's First Transverse Engine The i8's three-cylinder engine is mounted sideways in the car behind the passenger compartment to take up the least amount of longitudinal space—a key consideration with two powertrains to tuck into the chassis. That's exactly why engines are mounted crosswise in most front-drive cars and BMW should get used to this layout as it will be standard in the next-generation 1-series, which will be front-drive—and not guaranteed to come stateside. 10. An Mi8 Is Not as Farfetched as It Sounds Although no M version of the i8 has been announced or even suggested, it would not be difficult to create one. The 168-hp electric motor from the i3 could be easily fitted—with uprated electronics and a higher-capacity battery. Similarly, there looks to be room for the four-cylinder version of the i8's turbo triple. A proportional increase would raise its output to 304 horsepower, bringing this theoretical Mi8's total output to 472 with perhaps 500 lb-ft of torque. Even with a modest weight increase, this increased thrust, coupled to larger and sticker tires, and a suitably modified suspension, could easily produce the first hybrid M car. from Car and Driver Blog http://blog.caranddriver.com | |||
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Friday, August 9, 2013
Ten Things You Need to Know About the BMW i8
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