Does downshifting use more gas, or less?

Dear Car Talk

Dear Car Talk | Dec 01, 1993

Dear Tom and Ray:

Our names are Pete and Charley, and we've had an ongoing discussion for years about a certain subject. Your answer to this question will result in one of us getting a free breakfast. We've both agreed that your answer to this question will be considered gospel, so think out the answer very carefully.

Charley maintains that when you down shift, the engine speed increases, and therefore you are using more gas than if you didn't downshift. Pete says when you downshift, your foot is off the gas, therefore you can't be using any more gas. Who's right?
Pete and Charley

RAY: Sorry, Charley. What you may not realize is that there are two ways you can make the engine go faster. One is by stepping on the gas. Obviously, that uses more gas (even my brother can figure that out). Stepping on the gas makes the engine goes faster, which makes the wheels go faster.

TOM: But the opposite happens when you downshift. The spinning WHEELS make the ENGINE go faster. And in that case, you're not using any additional gasoline, because your foot's not on the gas pedal.

RAY: So does that mean you should downshift to your heart's content? Absolutely not. Downshifting is Number 15 on our list of "Ten Ways You May Be Ruining Your Car Without Even Knowing It" (we were never very good at math). And by the way, you can get a copy of the pamphlet by sending $3 to....

TOM: When you downshift, you may not be using any additional gas, but you're wearing out your clutch. So unless you're going down a long, steep hill, and need to keep your speed under control, we don't recommend downshifting to slow the car.

RAY: So if this discussion of yours has really been going on for a couple of years, you guys might as well just hold off on that breakfast. You can have it together while you're waiting for your clutches to be replaced.

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