Quote:
Originally Posted by dcb
You do need to be careful with this sort of comparison if you are going by EPA ratings as a measure of efficiency.
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This is something of a sore point for me, because in my world, there are all sorts of misleading measures of fuel efficiency. In my view, the only measure of
vehicle efficiency we have is the EPA tests (and careful constructed roads tests or computer models which emulate them, as nearly as possible.)
Driving techniques can change the numbers, but the change is a measure of
driving technique, not the
vehicular efficiency. (And your point is well taken that some transmissions effectively squelch hypermiling.) EPA survey results show that very few people actually practice hypermiling, so where sample size is large the surveys and EPA numbers match pretty well.
A couple years ago, Aptera was on the cover of Popular Mechanics with a huge 300 mpg headline. But the 300 mpg had absolutely nothing to do with vehicular efficiency -- it related only to driving profile -- they could have claimed 400, 600, 800, etc with exactly the same logic. I've always called the Zing a 100 mpg vehicle, because it gets that when operating on gasoline
alone, without any sort of hypermiling, with no change in battery charge level, and with my best approximation of EPA combined testing. Under that condition, Aptera was claiming 120 mpg for the vehicle that was promoted as 300 mpg by Popular Mechanics. The Aptera was, at that time, twice the weight and of greater frontal area than the Zing, and of not-much-lower Cd, so I was already skeptical re the 120 mpg.
I responded to the Aptera 300 mpg with my own equally valid calculation, based, like the Aptera, on a particular driving schedule... except that mine was more realistic, because I have actually done it, and because it represents a realistic average yearly accumulation. Their's was based on a hypothetical daily mileage of something like 100 miles (I'd have to look it up, or think too much, but don't have the time.) That's 36,500 miles per year -- far more than anyone would be likely to drive a two-seater commuter.
In my schedule, I drive 39 miles on electricity, followed by one mile on gasoline. I've gone 40 miles and have consumed 1/100 gallon of gas. 4000 mpg. In their case, they went something like 60 miles on electricity and 40 miles on gas: 1/3 of a gallon of gas, 100 miles: 300 mpg.
I could argue that my figures are more realistic, because 40 miles per day works out to almost the 15,000 miles that the EPA has used, and continues to use, as representative of an average driver's yearly accumulation.
So the Zing is more than 13 times as efficient as the Aptera, given a more realistic daily accumulation. Something is obviously haywire here. That's because in neither case, does the test measure the vehicle's efficiency.
The point being: I can give the Zing
any mpg figure I want (and Volt drivers do this, talking about 1200 miles per gallon, etc.) But I am not measuring the vehicle, I'm measuring the driving pattern... or in the case of hypermiling, the driver and his terrain.
Non-commercial interests and individual drivers can measure these things in ways that make sense to them, but
vehicle measurements need to be done by the same test to have any meaning, and to remain in the spirit of "truth in advertising."
At least that's my story, and I'm sticking to it.
