Monday, February 20, 2012

MPG Ratings

I find it funny how, when news agencies talk about things the public generally knows about, they can say things that are not the full and accurate truth but nobody really complains because they know enough of the facts behind the story and can fill in the gaps for themselves. But when people don't already know, all they see is the "truth" presented to them in the news story. In many cases, that isn't a complete enough picture.

Case in point, a recent article in the respected New York Times had an article about cars that can pass up the pump and there was a lot of good, if abbreviated information in there. For example, the last car they mentioned was the new Toyota Prius plug-in. They said:
"...the new Prius plug-in hybrid can travel just 15 miles on battery juice alone — one-third the Volt’s range — but it can top 50 m.p.g. when its gas engine comes into play, beating the Chevy."
 Now, almost any Volt owner knows what's wrong with that statement, yet it is technically correct in many ways. The *rated* gasoline mileage on a Volt is indeed 35 MPG. That assumes you are driving the Volt only on the gas generator with no power from the battery. But that practically never happens. And a casual reader of the NY Times would never get that. As Paul Harvey would say, here's the rest of the story.

First, a lot depends on how and how far you routinely drive. If you are like most people, your daily drive is within the Volt's approximately 40 mile battery-only range. So until you actually burn some gas, your gas mileage is infinite. If you occasionally drive in extended range mode, the gas MPG you use will average into your battery-only rating and will give you a very high MPG rating. We're talking hundreds of miles to the gallon. Add to this averaging the fact that you can get some "free" miles even when you are in extended range mode, running the generator, and you can easily beat the pants off of any hybrid. Prius plug-in included. An article in Green Car Reports spelled these "free" miles out pretty clearly. Some drivers report mileage as high as 45 mpg while the gas engine is running, not counting any averaging for electric miles. The short reason for this is that once the Volt has recharged its battery somewhat via regenerative braking (and unused juice from the generator, I imagine), it will then switch back to electric-drive mode for a few miles here and there. These miles get recorded under the gas-driven mileage, but no gas is being used while the car is driving them, so the official rating gets recorded as fewer MPG than the car actually got.

The MPG estimate stated in the NY Times article is quoting official figures. Officially, the Volt gets 35 MPG when running only on gas. They are correct to compare official numbers across the board, so when they quote a 15 mile battery-only electric range, they don't really need to explain that 15 miles is about the best you'll do in warm weather and city driving. Likewise, 50 MPG gas-only range is an official estimate. But article after article talks about how Prius owners find getting 50 MPG nearly impossible, as anyone who understands official MPG ratings can easily realize. Unless you drive like you have an egg between your foot and the gas pedal, and drive on flat terrain, at surface street speeds, it isn't going to happen. The Volt's official 35 MPG rating is, conversely, about the worst you can expect to get. My real, every day driving in a combination of city and freeway, in traffic and clear highways has given me an average of 685 MPG since I got the car in May of last year. And I have filled the 8 gallon tank one time since I got the car. (The tank was filled when I got it, so I've used about 7.5 gallons in 9 months.) My electricity usage has cost me $30 a month. The car is on a dedicated meter, so it's clearly separated out from the rest of the electric bill. Try to find a Prius driver who spends $30 a month to drive 32 miles a day, 5 days a week. You won't find one.

Good day!

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