Quote:
Originally Posted by D15r
In simple terms It's always more efficient to accelerate downhill than it is on the flat or up hill. But it needs to be applied with situational context and that's the tricky part which the driver has to compute :-P
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Its actually the other way around.
If you use your engine to accelerate down hills until the vehicle has XXX amount of energy, you will encounter higher wind speed than if you accelerate up a hill to get that same amount of energy.
That is because when you accelerate down hills, all of the energy is momentum.
When you accelerate up hills, lets say half of that energy is potential energy.
With some of the energy being in the form of potential energy, you don't encounter the same drastic wind drag losses that you would encounter if all of the energy were in the form of momentum (aka, high speeds).
Wind drag increases exponentially as speed increase, and it becomes quite costly as you go above about 60mph.
I calculated it once. It takes multiple times more energy to overcome wind drag at 80 than it does to overcome wind drag at 55.
So if you accelerate up a big hill, but hit a peak speed of 55, and then coast down the other side for 3 miles, one gallon of gas goes farther than if you spent that gallon of gas accelerating down the hill and plowing wind at 80mph.
Coast down one hill, you'll coast down to 45mph by the next hill. then accelerate up that hill, coast down the other side etc etc.
If you accelerate down that hill, you have to also overcome wind drag and still burn a lot of gas climbing the next hill.