If an electric car comes with an on-board range-extending gasoline engine, should its range per charge be given excluding or including said range-extending engine?
Traditionally, automakers have erred towards the side of caution, quoting range per charge as an ‘all-electric’ figure, but BMW USA has broken from the pack, advertising its 2014 BMW i3 BEVx range-extended electric car as having a ‘range per charge’ figure which includes both gasoline and electricity.
On the front page of its BMW i3 BEV model microsite, BMW proudly proclaims the all-electric variant of the i3 to have a range of somewhere between 80 and 100 miles per charge. Although official U.S. economy figures have yet to be released for the i3 or the i3 BEVx, what we know of European range estimates — and the fact that they are notoriously optimistic — we’d say BMW’s quoted range is reasonably accurate.
Yet on the BMW i3 BEVx model microsite, BMW quotes the range per-charge figure for the i3 BEVx as being between 160 and 180 miles.
A technicality of nomenclature
On paper this would appear to indicate the BMW i3 BEVx has a larger battery pack than its all-electric sibling. In reality however, this isn’t true: the BMW i3 BEVx and BMW i3 BEV are identically specced in terms of battery pack, electric motor and charging circuit.
So what’s going on? To explain, we think it’s worth looking at the way in which the car works.
The BMW i3 BEVx is sold as an all-electric car with a range-extending gasoline engine on board. Its purpose is to extend the useable range of the i3’s lithium-ion battery pack in emergency situations when there isn’t quite enough charge to reach the next charging point.
Unlike the Chevrolet Volt and the Toyota Prius Plug-in Hybrid, which will both run quite happily in gasoline-only mode for extended periods of time, the BMW i3 BEVx’s engine isn’t designed to operate for long periods of time. It’s something you’ll probably never really use — unless there’s an emergency, you need to go a little bit further than your car can comfortably cope with, or you have a charging station malfunction.
Further, unlike the Volt or Prius, whose engines stay off until the battery pack is completely depleted, the BMW i3 BEVx in certain markets comes with the ability to switch on the gasoline engine before the battery pack is empty. This has the effect of slowing down the rate at which the battery pack is depleted, since electricity from the battery pack is being supplemented by the on-board generator.
With that in mind, we’re guessing BMW executives think of the gasoline range-extender as literally enabling further all-electric range.
This leads to some very clever math, where range per charge could be seen as being equivalent to electric+gasoline.
Not ‘all electric’
Of course, the challenge here is the fact that while BMW is technically correct that ‘range per charge’ is as much as 180 miles, ‘electric only range,’ or range where the battery pack alone has provided motive power, remains at somewhere between 80 and 100 miles, depending on driving style.
Further still, because of the weight of the gasoline tank and range-extending engine, expect the BMW i3 BEVx to travel slightly less far per charge in all-electric mode than its all-electric sibling.
Had BMW quoted a ‘total range’ figure alongside an ‘all-electric’ figure, we’d be far happier — and we suspect many buyers would be too.
With so much confusion already in the electric car marketplace surrounding real-world range and charging requirements, we think it’s unfortunate that BMW has chosen to break from the normal nomenclature used when advertising plug-in hybrids and range-extended electric cars. Given the infancy of the market and the naivety of many of its would-be customers, we think quoting combined range figures as ‘per charge’ only serves to alienate rather than educate.
Moreover, with many salespeople using official automaker websites to provide ‘backup data’ for their own sales, we can see situations arising where customers — who do not fully understand the subtle difference between range and all-electric range — buying a car believing it to travel almost double the distance it is capable of in electric-only mode.
But what do you think? Is BMW being fair? Is this one nuance too far?
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