At what speed is highway mileage calculated?

The Chevrolet Equinox with a four-cylinder engine is advertising 32 mpg. At what speed is this calculated? Also, if we drive to Colorado on Interstate 80 with a speed limit of 75 mph, what kind of mpg could I expect at 75 mph? Would I be better off with the six-cylinder?

Paul B., New Lenox, Ill.

To answer your last question first, if fuel economy is a concern, you’re much better off with the 2.4-liter four-cylinder in the Chevrolet Equinox than the optional 3.0-liter V-6. With front-wheel drive, the four-cylinder Equinox’s EPA mileage estimates are 22/32 mpg city/highway. With the V-6, the numbers drop to 17/24 mpg (25 percent lower for the latter). The estimates for all-wheel-drive versions are 20/29 mpg with the four-cylinder and 16/22 mpg with the V-6.

2011 Chevrolet Equinox

Can you achieve these highway estimates cruising at 75 mph? Probably not, though you may come close if you keep the windows rolled up, don’t overload the vehicle with people and cargo (or put stuff on the roof) and maintain a steady pace (cruise control helps).

We have tested the Equinox many times, and it is the most commented-on model regarding varying fuel estimates that we’ve ever encountered. It seems to be a hot-button topic on internet forums and blogs. We even wrote a blog post on how the Equinox didn’t hold up to its 32 mpg rating during a recent mileage test.

The EPA says a vehicle that gets 30 mpg at 55 mph will drop to about 28 mpg when the speed reaches 65 mph and fall to 24 mpg once you hit 75 mph. In our experience, the speed penalty is less than that, and we usually match or exceed the EPA highway number if we keep it under 70 mph. That is for a tank of gas, not brief readings from trip computers that can give false impressions. Your results will vary, of course, depending on the vehicle, the load, weather and your driving style.

The EPA derives its estimates from driving simulations done in a laboratory. The highway simulation covers 10.3 miles at an average speed of 48.3 mph, with about half the time spent at 55-60 mph. Not exactly real-world. Since 2008 the EPA has included an 8-mile trip that adds more aggressive acceleration, spurts up to 80 mph and more than half the time over 60 mph — somewhat closer to reality. Neither test runs at a steady speed, the kind of driving you will likely do and an approach that should improve your mileage.

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Answered by Rick Popely on May 4, 2011 in Chevrolet , Chevrolet Equinox , How Does That Work? | Permalink

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