If city fuel economy differs by 2 MPG and highway by 4 MPG, shouldn't the overall economy, which represents a composite of both, be expected to differ somewhere from 2-4 MPG, rather than by just 1 MPG?
The PR geniuses at Consumer Reports seem incapable of explaining this but instead simply refer back to the very numbers printed above, or they congratulate themselves for doing such a fine job answering customer inquiries.
As I understand it, the fuel economy numbers are determined by a strict protocol. You run the course and write down the numbers. Why is this such an issue for you? You ain't gonna achieve those anyway. Bitchin' about it ain't gonna change anything.
why don't you be more honest and say that this is simply your uninformed guess? "likely" and "probably" are /neither/ if you can't be bothered to at least find out how the numbers are complied.
Good point. And in the next issue (March 2012) they report on the Prius V that it gets higher MPG on the highway than in the city (city / highway 33 /
47). EPA's numbers are city / highway / combined: 44 / 40 / 42. All Toyota hybrid vehicles get greater city MPG than highway which everyone knows is due to the configuration of the drive system to run on electricity alone between intervals of highly efficient charging to restore the battery charge level when the vehicle is driven slowly. Here's an example: I got caught in an L.A. rush hour jam for 3 hours a few of years ago with my 05 Prius. When I finally reached my daughter's home I was surprised to find the average MPG since the last fillup read 56.3. I'm sure everyone's experience in a traffic jam with their fully warmed-up Prius is similar. The thing is just damn efficient when driven slowly.
But why did Consumer Reports change this relationship in their spec listing of the Prius V? Did they forget to properly warm-up the vehicle for their testing? Or was it just a slip-up by the copy writer and the proofreader? Or are they doing the auto industry a favor by slyly listing numbers that hide the great advantage of Toyota's Hybrid Drive System over the competition?
I usually achieve their highway numbers, and their city numbers seem accurate for heavily conjested traffic, but I don't drive like an angry madman who tries to make trouble.
Here is what CR says about their fuel economy test:
"We perform our own fuel-economy tests, independent of the government's often-quoted EPA figures and the manufacturers' claims. Using a precise fuel-flow measuring device spliced into the fuel line, we run three separate circuits. One is on a public highway at a steady 65 mph. That circuit is run in both directions to counteract any wind effect. A second is a stop-and-go simulated city-driving test done at our track. The third is a 150-mile "one-day trip" using several drivers taking turns around a 30-mile loop of public roads that include a highway section, secondary roads, and rural byways. CR's overall fuel-economy numbers are derived from those three fuel consumption tests."
I don't think there is anything unusal about the variatation in the results.
While the 65 mph steady state test and the simulated stop and go test might be repeatable, I suspect the results of the 150 mile trip are subject to a lot of varability since it is run on public roads with multiple drivers (traffic variations, driver variations, weather variations, etc.). Since CR uses the results of all three tests to come up with the overall number, it seems to me that variations in the 150 mile test could significantly shift the overall number reported. Also, since they are reporting interger numbers, it is possible that the 17 is really a 17.4, the 37 is really a
37.4, the 19 really a 18.5, the 41 really a 40.5 the 27 is really a 27.4, the 26 is eally a 25.4, etc.
In my opinion the repeatability of these measurements is no better than +/-
1 mpg (and probably no better than +/- 2 mpg), so there is nothing unusal about the results. Would you have felt better if CR reported the overall Fuel economy as 27 +/1 mpg and 26 +/- 1 mpg?
They are trying to provide basic infomations and not confuse housewives. If you want precise numbers, you'll proably have to do it yourself - particualy since real world fuel economy is highly dependent on driving style and where the car is driven.
I have a 2011 Fiesta. I've never seen mileage as high as the CR highway mileage (even on a trip from Florida to NC with no city driving) and never as low as their stop and go (even when commuting in stop and go traffic), and my overall is 2 mpg better than theirs. I don't think their numbers are wrong, but different drivers and conditions will acheive different results. When my SO drives my car, she usually get 1 to 2 mpg better than me. Same car, same roads, different driver. The CR numbers are a general indicator, not a precise measurement and likely different than what you will do.
Don't you suppose Toyota programs the computer in the their cars to achieve the best numbers possible in the EPA test? The EPA test is well defined, run indoors on a dynometer, is highly repeatable and the results are used by the Government to determine compliance with US fuel economy regulations. CR's test uses higher highway speeds for the highway test and I suspect their stop and go test has a lot more stop and go than the EPA city loop. It is far less repeatable than the EPA test. I asusme Toyota could adjust the programing of the PCM to do better in the CR test, but then if might not do as well in the EPA test. Which would you optimize for?
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