Small Engines May Use More Fuel Than You Expect, In Europe Especially

Decreasing an engine's displacement is one of the most straightforward ways to increase fuel efficiency.

Or is it?

According to research firm Emissions Analytics, the high fuel-economy ratings of downsized engines may not always translate to the real world.

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Claiming to have tested over 500 model variants, researchers say vehicles with smaller engines can have more difficulty replicating their rated fuel economy in the real world because of the way they're driven.

Abrupt acceleration is bad for fuel economy, particularly in smaller engines, which have to rev higher and harder to produce the power needed for quick speed changes.

This is not something that's apparent in the gentle and controlled conditions of fuel-economy testing, researchers say. And it produces increasing discrepancies between ratings from those tests and real-world results.

Researchers analyzed vehicles by engine size, and measured the variance between government-rated fuel economy and real-world test results.

For U.S. test cycles--which they noted are "much harsher" than those in Europe--the variance between the EPA combined rating and the real-world figures stayed within 3 percent one way or another.

Smaller engines had slightly higher variances, but all were well within the range produced by more or less aggressive driving styles.

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Averaging all results together, researchers concluded that cars sold in the U.S. tend to come pretty close to the combined fuel-economy ratings on their window stickers.