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Old 11-18-2013, 05:16 PM   #14 (permalink)
sheepdog 44
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Join Date: Dec 2011
Location: Salt Lake valley Utah
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I would suggest you get a scangauge to make it clearer in your daily driving.

One of your misconceptions is that driving slower (and therefore longer) going uphill wastes more fuel than keeping a constant and faster speed. Such is not the case. You are in fact easing the throttle to gain more mpg as you use momentum to crest the hill.

For extended hill climbs you do want to maintain a minimum mph speed so you keep your engine and transmission in an efficient zone. For example, 40mph would be good. A constant 5mph going up a long hill is terrible! For smaller hills you can bleed more speed.

Your second misconception is that the increased aerodynamic resistance going downhill is ENOUGH to NEGATE the benefits of the increased speed and kinetic energy. That is not the case until you get past 75-80mph depending on how aerodynamic your car is. Cresting a hill at 40mph, then reasonably accelerating downhill to 65mph doesn't increase aerodynamic resistance enough to be unbeneficial.
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