Carrying excess weight
Myth: It doesn't matter if there's a set of golf clubs, briefcases, and other junk in the trunk. The minor weight won't affect fuel economy.
Fact: The US Energy Department says that an extra 100 pounds in your vehicle can reduce fuel economy by 2 percent, so don't carry more than you need. Car manufacturers put their cars on gram diets, trying every weight saving measure possible to increase mileage.