Speed comes at a price....
65 mph vs 60mph = 6.4% decrease in fuel economy
70 mph vs 60mph = 10.9% decrease in fuel economy
75 mph vs 60mph = 17.3% decrease in fuel economy
Pushing air isn't easy
Between 55 and 60 MPH, 50% of the fuel is used to overcome air resistance, the remaining 50% is used to overcome the load. The percentage of fuel needed to overcome air resistance increases dramatically as speed increases.
According to GM:
Drive the speed limit. Gas mileage decreases rapidly at speeds. On a typical SUV, for every 10 miles-per-hour average speed increase, you can lose four miles-per-gallon of fuel economy. In addition, for some drivers, using cruise control on the highway could help save as much as 10 percent.
http://www.gm.com/company/gmability/...ab_111805.html
There is a direct relationship between how much gas your car consumes and how fast you drive. It is a curve and the peak is around 55 mph. When you are going too fast or too slow, you use more gas.
http://auto.howstuffworks.com/framed...ning/speed.htm
As a rule of thumb, you can assume that each 5 mph you drive over 60 mph is like paying an additional $0.20 per gallon for gas.
http://www.fueleconomy.gov/feg/driveHabits.shtml
Conclusion.
Driving the speed limit, 7-23% increase in FE, saving $0.16-$0.53 per gallon
Reducing weight by 100 lbs, 2% increase in FE, saving $0.02-$0.05 per gallon
Note: Cost savings are based on an assumed fuel price of $2.31/gallon.
Annual FE improvement and money saved:
36 MPG car driving 400 miles per week
Cost per year = $1334
Same car with weight reduction and Reduced speed
25% total increase in FE.
45mpg and $1067 per year
You save: $267.00 per year
or $5.13 per week
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