Tires are a common culprit when it comes to bad fuel economy. Certain tires are actually designed to create less resistance and better gas mileage. You might find that a knobbier all-terrain or snow tire produces the opposite effect. Beyond tire design, look for the following:

Low Pressure: If your tires are low on air, they will have more surface area in contact with the road, creating a greater rolling resistance. Try rolling a flat beach ball and then one filled with air as an example — air pressure makes a big difference.

Alignment Issues: Wheels that are not properly aligned will cause tires to contact the road unevenly, again producing more resistance while also wearing tires more quickly.