California is pressing for more cars to be fitted with fuel efficient tires. In this article they state that most cars come from the factory with fuel efficient tires on them. The problem is when these tires are replaced. Most people are doing so with less efficient tires. They go on to say that if more cars were fitted with sensors letting the driver know when the tire pressure is low, and drivers were to check their tires more often, this could save more than 500 million dollars annually.