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When spotting a red light or similar, I often release the gas pedal, gear down and let the engine decelerate instead of pressing the brake pedal. I was taught that this was more energy efficient for some reason, but I never really understood why. Is thIs true?

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Might be worth reading mechanics.stackexchange.com/questions/1210/… –  Cornelius Jun 14 '14 at 11:38
I've removed two theoretical answers, including the accepted one. Please remember that we don't allow answers based on mere theoretical models - you have to link to evidence. –  Sklivvz Jun 16 '14 at 22:53
The only efficiency claim is one that I've anecdotally tested with the trip computer on the car. Downshifting to higher revs, and coasting, causes the instant fuel consumption to report 0.0l/h. But braking only reports 1.1l/h (l/h is used over l/100km when not throttling). So hardly a massive difference in economy, and personally not worth the extra wear on the gearbox. But also sounds very, very cool if you have a large capacity engine or a nice exhaust. –  Mark Henderson Jun 17 '14 at 3:37
I think there was even a mythbuster episode where they tested all of this quite precisely. Depending on the conditions I would say that I personally save 10-15% with this style, as this is about the only major difference in me and my wifes driving style. –  PlasmaHH Jun 18 '14 at 10:03
When you gear down you use the inertia of the vehicle to turn the engine over thus the resistance of the engine slows the vehicle. Converting the inertia of the vehicle in to energy to turn the engine over means you do not have to use fuel to do that. - my own understanding –  Mark Price Jul 4 '14 at 16:12

protected by Community Jul 4 '14 at 1:31

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