Y YMMV
(Why Your Mileage May Vary)
(the truth behind the infamous EPA fuel economy figures)
So what's with the EPA stickers so prominent on new cars? Almost nobody believes them. They typically have wording ("Actual Mileage will vary…") in which they hedge their bets.
The problem is that when measured, consumers typically get MPG figures less than promised (excuse us, estimated) on the sticker. Few people get the same results and nobody, it seems, gets higher.
It turns out this is not just anti-government paranoia at work; there are good reasons why the public perceives these "estimates" to be unreliable. Consumer Reports tells us that 90% of the cars they test return worse MPG than what the EPA ratings are and that the average discrepancy is 9%.
Part of the reason is that the car manufacturers "tune" their cars so they do well on the when tested for their MPG rating. Since the EPA ratings are a competition that in effect awards extra $$$ to the winner, who can blame them?
The larger reason behind the discrepancy can be found in the way the EPA tests the cars. They are tested in a laboratory on a dynamometer which stimulates the car being driven. A predetermined driving routine, or schedule is strictly followed for the sake of consistency.
A look into the test routine reveals the problem. The driving pace is less than moderate; if you drove the way the EPA seems to think we all do your grandmother would be yelling "Hurry up already!". Maximum speed is 60 MPH. Acceleration, for the city test, is 3.3 mph/sec which works out to 18.2 seconds to go from a stop to 60 MPH. This is a very leisurely pace that is rarely observed in the real world.
Other problems: Hills are not part of the driving cycle, accessories (such as air conditioning, etc.) are off during the tests and cold weather is not part of the mix. All of these items can adversely affect the fuel economy of a automobile.
There is hope however. The EPA is revising their testing methods and schedule starting with 2008 cars. Highway speeds will now top off at 80 MPH - yes, we know that is usually illegal! More realistic acceleration rates, specifically 8.46 mph/sec or about a 7.0 second zero to sixty MPH, will be used. Cold climate testing will be included and air conditioning will be used.
What will the result likely be? Our prediction is that at first there will be some confusion, as consumers compare figures generated under the new system with those from the older system. Indications are that hybrid vehicles will see more of a drop in their MPG figures than non hybrids. The EPA says we can expect the CIty MPG rating to fall from 12% to as much as 30% and that Highway figures will drop an average of 8% to as much as 25%.
Our reward for tolerating this confusion is that we will have more realistic figures to help make car buying decisions. You mileage however, as before, may vary.
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