How much does speeding really affect your fuel economy?
Consumer Reports drove five vehicles at 55, 65, and 75 miles per hour. They found that driving 200 miles at 75 mph instead of 55 mph saves you an hour's drive time, but it wastes about $5 to $7 in gas.
So for a thousand miles, driving 75 mph costs you an extra $30 or so.
As far as saving time, you also need to factor in those extra trips to the gas station.
These gas mileage tips can help you reduce the amount of gas you use. If you are already following these tips, you are probably getting the best gas mileage your car can deliver.