According to AAA, about 80 percent of the cars on the road are driving with one or more inflated tires. Tires lose air through normal driving, especially after hitting pot holes or curbs, permeation and seasonal changes in temperature. They may lose one or two psi per month in the winter and even more in the summer. And, it is not possible to say if they are properly inflated just by looking at them. Not only is inflation low for your tires, but it is also bad for your gas mileage, it affects the way your car drives and is generally unsafe.
When the tires are inflated, the tread wears out more quickly. According to Goodyear, this equates to 15 percent fewer miles than you can drive in them for every 20 percent you are under-inflated. Deflated tires also overheat more quickly than properly inflated tires, which causes more damage to tires. Areas faded below indicate areas of excessive tread wear.
Because the tires are flexible, they flatten on the bottom when they roll. This contact patch rebounds to its original shape once it is no longer in contact with the ground. This rebound creates a wave of movement along with some friction. When there is less air in the tire, that wave is larger and the friction created is greater and friction creates heat. If enough heat is generated, the rubber that holds the tire strings begins to melt and the tire fails.
Due to the extra resistance that an inflated tire has when it rolls, the engine of your automobile has to work harder. AAA statistics show that tires that are inflated by as little as 2 psi reduce fuel efficiency by 10 percent. More than a year of driving, it can amount to several hundred dollars in extra gas purchases.
The self-inflating tires, on the other hand, are designed to constantly maintain the tire pressure at the right level. Self-inflating systems are designed more for slow leaks and to optimize performance and safety than to keep a vehicle moving on a tire that can no longer contain air.