View Single Post
Old 10-18-2017, 07:07 PM   #13 (permalink)
Join Date: Jul 2017
Location: Wisconsin
Posts: 48
Thanks: 20
Thanked 8 Times in 5 Posts
Originally Posted by D15r View Post
Your adding in a lot of varibles, who said anything about what speeds are involved? It takes more fuel to accelerate up hill than it does down hill, that can't be argued. Adding varibles it can be argued as you have done so.
It takes more fuel, because the vehicle is gaining potential energy in addition to momentum. More of the fuel gets turned into energy, and the vehicle goes farther with that amount of energy because it is not encountering as much wind drag.

Per unit of fuel burned, the vehicle gains more energy when accelerating up hill.

There are also fewer parasitic losses (due to less wind drag). So, the vehicles potential energy is used to move the vehicle forward (while coasting down the hill) rather than plow through wind at the higher velocities that would be encountered if you use that same amount of fuel to accelerate down the hill.

As far as the amount of energy it takes to climb the hill, it doesn't matter how fast or slow you do it. It takes X amount of energy to move your vehicle up to the top of that hill, whether you're coasting or not.

Energy consumed while climbing the hill is a recoverable loss. Energy consumed to overcome wind drag (which increases exponentially with speed) is NOT recoverable.

Not only is more of the energy recoverable when you use it to accelerate up the hill, but the vehicle operates closer to WOT. That means you are operating in a part of the engine's power band that has a more efficient brake specific fuel consumption. Translation: Your car gains more energy per unit of fuel that is burned.

Its not even about context. The engine does more work per unit of fuel when accelerating up hill. The vehicle has a lower peak speed, so there is less non-recoverable energy lost to overcome wind drag.

If two identical cars are each filled with one gallon of gas, and driven on the same hilly road, the guy who accelerates up hills will travel farther before running out of fuel than the guy who accelerates down the hills.
2007 Silverado 1500 2wd flex fuel with active fuel management. 33" Nitto Terra Grappler tires. 2.5" motofab front end leveling kit.

Last edited by Panther140; 10-18-2017 at 07:17 PM..
  Reply With Quote