Misleading Metric: Max EV Speed for Conventional Hybrids

Last week, the U.K.’s Advertising Standards Authority (ASA) stopped Porsche from running an ad claiming that the new Cayenne S Hybrid “can even travel to a speed of 37 mph without using its V6 petrol engine.” The agency believes the 37 mph claim is misleading because the vehicle travels only for a limited time and distance using power exclusively from the electric motor and batteries. The ASA is right. Hopefully, the ruling will raise awareness that the ability for conventional hybrids to travel in “all-electric mode” at high speeds is a cool trick—but relatively insignificant.

Porsche is not the only hybrid maker trumpeting the all-EV capability of its conventional hybrids. Ford promoted the Ford Fusion Hybrid’s ability to travel up to 47 mph without using gasoline. The 2010 Toyota Prius’s “EV” button allows drivers, under some conditions, to force the engine off, allowing the car to run up to 25 miles per hour from battery power alone for about one mile.

As any driver of a full hybrid—or a plug-in car—will tell you, it’s a magical feeling when a vehicle moves down the road without gasoline in near silence. But in the case of a conventional hybrid—rather than the plug-in kind—the net result of maximizing the EV mode is to quickly drain a battery that was not designed for high demand all-electric driving. Just like when you need to catch your breath after a long sprint, the hybrid’s gasoline engine is more likely to come on stronger and longer to refill that battery to an optimal level. In the end, that undermines the hybrid’s core efficiency strategy of juggling different aspects of the drive cycle with the best mix of gasoline and electric power. The mixing and matching of electricity and gasoline is how a vehicle like the Toyota Prius can achieve a remarkable 50 miles to the gallon.

Efficiency vs. Electricity

So, it’s a nice claim to say that a hybrid can travel X miles per hour all-electric, but the likely net result of high-speed EV mode is reduced MPG. This once again proves that the name of the game is efficiency, not electricity.

By the way, Porsche also says that the Cayenne hybrid can “sail” on electric power at speeds up to 97 mph.

The empty Porsche claims underscore that if you’re driving a non-plug hybrid, all of the energy to move the car ultimately comes from the gas engine—and all-EV mode is not going to last very long. This doesn’t mean that a hybrid’s all-electric mode is lame. Not at all. For example, it’s incredibly useful when traveling short distances at low speeds. That’s why Praveen Cherian, Ford’s hybrid program leader, speaking about the Ford Fusion Hybrid said the EV mode in conventional hybrids “allows drivers to maximize fuel efficiently in many driving situations. For example, this would allow drivers to travel around their subdivision and parking areas in all-electric mode.”

But the claim that a hybrid can travel up to 30 or 40 or 50 miles per hour in all-EV mode, even if true, is mostly a clever marketing claim that should be taken with a grain of salt.

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  • usbseawolf2000

    A few months back they were claiming 97 MPH in EV. Just google it. What a disappointment huh?

  • hannah

    I was planning to get this hybrid car assuming i could do local travelling for “free”, but now will have to reconsider esp as car can only do limited mileage on electricity, so what the hell are they charging so much for, its a joke…..

  • Anonymous

    I have a 2010 Prius and I stopped using the EV mode as often as I used to. The experience is, if I use it for a long time, it really drains the batter (as expected) and you pay later on the price, where the conventional engine does not turn off since it has to recharge. It all depends on the type of road. I can make good use of the EV button if I know the type of roads ahead. If I’m e.g. in slow highway traffic, I turn EV on, if I know there is a downhill stretch ahead that helps recharging the battery. But using the EV button at the wrong times, can do more damage than good (to the mpg). But in general, it seems to be wise to let the Prius decide when to turn the engine off, but if you know what’s ahead, you can make decisions a little bit smarter.

    Some people also claim you will reduce the battery life by using the EV mode to often and constantly drain and recharge the battery – but I’m not expert enough to comment on this … maybe the hybrid pros can comment on this.

  • Phillip U.

    Is this really news? As far as I know, every full parallel hybrid has this same limitation to varying degrees. Mine can go up to 25-30 mph if I don’t floor it. It’d be nice if it could go faster without firing up the gas engine because then the low end speed range which uses a lot of fuel to get through can be really efficient and once I’m at highway speeds, the charging will return that energy to the battery. That’s the way they’re supposed to work.

    @hannah: are you being serious at all? You would think about buying a Porsche for “free” travelling?

  • billbob

    What about the Tesla model-S?

  • tapra2

    The ASA is right. Hopefully, the ruling will raise awareness that the ability for conventional hybrids to travel in “all-electric mode” at high speeds is a cool trick—but relatively insignificant.Engg Blog