The Chevy Volt: As Efficient As You Want It To Be
If the recent flap over the Volt’s drivetrain has taught us anything
it’s that A) GM’s internal-combustion-assisted plug-in is more
complicated than we thought, and B) GM is fine with simplifying its
complex reality in order to make it appear as attractive as possible.
Which is just fine: they’re the ones trying to sell a $41k car, and as
such they’re entitled to do what they can to make it seem worth its many
shortcomings. What the automotive media needs to take away from the
brou-ha-ha isn’t necessarily that GM’s hesitance to bring forward “the
whole truth” is an intrinsically big deal (let’s just say this wasn’t
the first time), but rather that knowledgeable writers should focus on
explaining the Volt in ways that are both comprehensible and fully
accurate. In this spirit, the most important question isn’t “what should
we call the Volt?” but “how efficient is the Volt in the real world?”And
on this point, there’s plenty of room for some truthful clarification.
But as with questions of the Volt’s taxonomic category, objectively
analyzing the Volt’s efficiency requires a certain amount of semantic
clarity. After all, unlike any car that has come before, the Volt
operates in two discrete modes: “EV mode,” in which it drives on pure
electrical energy, and “Charge Sustaining” or “CS Mode,” in which its
gas “range extending” engine generates electricity and (under certain
circumstances) even sends torque directly the Volt’s wheels. Unlike a
Prius (or other parallel hybrids), the Volt doesn’t continuously vary
between gas and electric drive, but runs on pure plug-in power until the
battery reaches 30 percent capacity, and then switches to CS Mode.
Because of this drivetrain concept, it’s crucial that EV Mode range is
presented separately from CS Mode MPG. After all, combined MPGs from a
trip using both EV and CS modes will depend entirely upon the length of
the trip. If a trip lasts (say) five miles longer than the EV range
(say, 40 miles in EV mode and five miles in CS mode), and the car
returns (say) 50 MPG over those last five miles, it will have burnt .1
gallons for the entire trip, resulting in an average MPG of 450 MPG. But
if you charge the car’s battery once (giving another hypothetical 40
miles of EV range) and then drive 450 miles (410 of which burn gas at
the hypothetical rate of 50 MPG), you’d be lucky to get 55 miles per
gallon for the trip. In short, how often you recharge the Volt’s
batteries is the single defining factor in determining an overall MPG
rating for the Volt.
And this reality is already leading to confusion. Over at Motor Trend,
former TTAC writer Jonny Liebermann claims to have wrung 127 MPG out of
his Volt tester, gushing
Broken down, over the course of 299 miles on Los Angeles highways,
byways and freeways, the Volt burned 2.36 gallons of gasoline (fine,
2.359 gallons — we rounded up). Most other cars use up a tank of gas
going 299 miles. The Volt, to reiterate, used 2.36 gallons over 299
miles. That’s freaking amazing!
Unfortunately, Lieberman prevents us from concurring with his breathless
assessment by failing to include an accurate log of the trips he took to
achieve that number. Working backwards through his
less-than-scientifically-presented data, we reckon Lieberman got about
52.6 MPG in CS mode, with at least one battery recharge somewhere in the
middle. That’s better than the consensus forming around the Volt’s
CS-Mode efficiency (somewhere around 35 MPG according to Popular
Mechanics and Car & Driver), but it’s still nowhere close to supporting
127 MPG as a consistently-achievable CS Mode rating (it’s also a number
that GM would likely not stand by if pressed).Unsurprisingly, this
hasn’t prevented GM’s social media and PR team from sending copious
numbers of detractors to Lieberman’s piece by way of “educating” them.
Of course, Lieberman’s analysis is not without value: it shows that the
Volt can achieve 127 MPG in “normal” driving. But with an extra
charge-up somewhere in his poorly-defined test, he could easily have
achieved twice that number (think the infamous “230 MPG“). Without an
actual trip log showing how much gas and electricity were used on each
leg of his test, however, Lieberman’s 127 MPG number means nothing. By
using it as proof that the Volt is indeed a “game changer” GM’s PR team
is simply proving the extent to which they’re willing to exploit
confusion (even among the august ranks of buff book contributors) in
order to hype their car.
At the end of the day, the Volt’s efficiency will most accurately be
represented to consumers by outlets that test EV range and CS mode range
independently and transparently. Actual EV mode is important, because it
will give consumers a real-world sense of how far they can go without
using any gas (i.e. whether their commute is short enough to use the
Volt regularly in EV mode alone). CS mode MPG is also important because
it tells consumers what they can expect when the Volt’s EV range is
expended. Any attempt to fuse the two into a number that can be compared
to the MPG of a Prius or Escalade must be clearly qualified by a
transparent accounting of the trips used to get that rating.
Thus far, a consensus on these points is building:
Popular Mechanics calculates a 33 mile average EV mode range, and
between 32 and 36 MPG in CS mode.
C&D claims between 26 and “the upper 30s” for EV range in miles, and 35
MPG for CS mode.
We’ll keep a close eye on efficiency test results for the Volt, and
report them here at TTAC in terms of EV range and CS mode efficiency.
Anything else would be less than the whole truth.
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