Fuel Efficiency – Constant Throttle / Load versus Cruise Control

So, in case any of you were wondering what was happening with my Twitter posts regarding driving with Cruise Control (constant speed) versus Constant Throttle (variable speed), I thought that I would add some detail.
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I\’m occasionally a hyper-miler, it entertains me on the road, and when I\’m road tripping with family or friends has an added sense of accomplishment and bragging rights. One time I remember most was in driving to Oshkosh, Wisconsin when my dad and I competed to get the best mileage. I beat my dad by a solid mile per gallon, and he beat the cruise control by a mile per gallon (in all cases over extended highway driving, Atlanta to Wisconsin.) To add to my credentials, I drive with a air flow computer in my car that tells me my current throttle %, airflow percentage, and more.
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One of the people I was responding to on my twitter post was irritated because the other had just driven a 6 hour + drive, and apparently not been maintaining a constant speed. I thought it might be worth the funny point to point out that driving variable speed can potentially be more efficient.
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To effectively drive more efficiently with variable speed you should do the following.

  • Only drive within a power range that you can stay in your top gear. If your car is struggling without downshifting, then you are going to slow to get all of the advantage from variable speed.
  • Have a maximum position that you are willing to put the throttle. In my car, I like to have this max set at 60%.
  • Make sure that you maintain a highway speed
  • Predict the open lane so that you aren\’t braking (ie throwing gas away.) Particularly, try to be nice, and move to the right before up hills and figure out how to move back left for the downhill.
  • Accelerate a lot on downhills, just maintain as much speed as you can on the uphill.

I imagine that the people in question were not driving with a \”constant throttle\” system and were instead just forgetting how fast they were going and slowing back down, or doing the opposite of what this system is supposed to do and accelerating to pass in an uphill.

This method will accelerate you on downhills (to probably faster than you want to go) and put you in a crawl going on an uphill, which is a decent way to remember that going with gravity is easier than going against it.

My father taught me to drive like there was an egg between my foot and the pedal, meaning that I\’m never changing throttle too much or too quickly.

Best of luck driving.