Yes! Each car is unique, and exact numbers will vary between models, but gas mileage sharply declines at speeds over 60 mph. It’s estimated that for every 5 mph faster (over 60) you drive, it’s like adding a quarter to every gallon of gas bought. It is another incentive to drive the speed limit! Weight also has an impact on gas mileage. The heavier the load, the worse the gas mileage.
I agree with the above answer, from research and personal experience. Most cars get the best gas mileage at 55 mpg. Any faster and the engine has to work too hard to overcome air resistance.
How fast you accelerate has a huge impact on your mpg’s. I remember watching a documentary (Click and Clack Search for a Green Car Future) that said accelerating hard uphill will get 6 mpg from a car that normally gets 30!
Another example of poor accelerating worsening mpg’s: Top Gear has a Prius drive as fast as possible around a track with a BMW following. The Prius got worse mpg because it’s smaller engine had to work much harder than the BMW.
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Yes, fuel efficiency works on a bell curve. Anything less than ~15mph and anything over ~60mph tends to make any vehicle’s engine work harder. Basically, extreme low and extreme high speeds prevent vehicles from using momentum.
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