IEEE Spectrum April, 2015 - 49

price: us $136,650 power train: 96-kW
(129-hp) aC electric motor with 1.5-l 170-kW
(228-hp) three-cylinder gasoline engine
overall fuel economy: 8.4 l/100 km (28 mpg)
on gasoline; electric equivalent of 3.1 l/100 km
(76 mpge)

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 batterystuffed 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 flatsix 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. n

Rolls-Royce Wraith
Satellite to Earth:
Downshift a bit
For 111 years, the rolls-royce experience has been
all about wafting, often in chauffeur-driven comfort.
now the stunning wraith coupe adds a computerized
wingman, using gps data to automatically select the
perfect gear for the road ahead. the wraith's satelliteaided transmission (sat) is a production-car first for
the BMw-owned rolls-royce.
rolls-royce engineer phil
harnett, formerly with BMw's
Formula one team, saw a colleague working on sat as a predevelopment project. "i saw
how perfect it was for rollsroyces-dynamic yet effortless-
and brought it into the wraith,"
harnett says.
this yachtlike fastback
coupe marries a 465-kilowatt
(624-horsepower) V-12 to the
silken, eight-speed automatic
transmission produced by the
ZF group, based in germany.
But the wraith takes the ZF
unit to the next level, adapting to a driver's individual style

and applying gps route and
location data to anticipate and
change gears. the engine's
electronic control unit adds
an algorithm that responds to
upcoming road patterns.
rolls-royce spokesman gerry
spahn says the system works
especially well on curvy terrain,
off-ramps, or roundabouts. as
the car heads into a series of
price: us $298,225 power train:
465-kW (624-hp) 6.6-l twinturbo V-12 overall fuel economy:
15.7 l/100 km (15 mpg)

curves, for example, the sat will
automatically hold a lower gear
to prevent midcorner upshifts
and to avoid upsetting the car's
occupants with needless gear
changes. in testing on public
roads, the system has reduced
the number of automated shifts
by up to 30 percent, spahn says.
Besides reducing wear and tear
on the transmission, the system
also improves responsiveness
and fuel economy. Because it
requires no additional compo-

nents beyond existing sensors,
controllers, and the navigation
system, no weight is added to
the vehicle.
the sat isn't mapped for altitude and topography, so it can't
anticipate hills and change
gears accordingly. But that kind
of functionality could be baked
into a future version.
"Customers have asked about
altitude," spahn says. "it's not
technically impossible; it just
hasn't been applied." n

Table of Contents for the Digital Edition of IEEE Spectrum April, 2015