![]() So it’s very possible a hilly path might get better mileage than a level one. ![]() However, a couple of posters brought up a couple of pretty good points that I hadn’t thought of before in that an engine may operate at a higher efficiency when working harder than just going over a level surface. Even without any downshifting/braking there’s probably going to be some degree of engine braking as long as the car is in gear. So initially that would tell me that going up and down a hill would require more energy than going level because a lot of energy would be wasted through downshifting/braking when going down hill (rather than just coasting down the mountain like a rollercoaster). Then there is the fact that one would probably have to down shift and/or brake going down hill in order to reduce speed. Because gravity is working against and working for the car the same amount of work then the difference between going up and down a mountain should cancel out, making it the same as driving over a level roadway. However, when the car goes down the mountain gravity now works with the car. Work is the dot product of force and distance and when you’re going against gravity (you’re driving uphill) less of the force that your car is exerting is going to making it go forward. When going up the mountain the car has to work harder because not only is the car working to accelerate itself forward it’s also working against gravity. To simplify things, in this case the only difference between going 100 miles up and then down a mountain (and returning to the same elevation) or going 100 miles over level roadway is gravity. Basically, if all friction/drag/etc were eliminated and the car (and engine) had the same efficiency at all speeds it wouldn’t matter what path the car takes.
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