Is it true that driving with soft tires wastes energy and results in more pollution?
— Nanci Graham, via e-mail When tires are not inflated to the pounds per square inch (PSI) rating recommended by manufacturers, they are less “round” and require more energy to begin moving and to maintain speed. As such, under-inflated tires do indeed contribute to pollution and increase fuel costs. An informal study by students at Carnegie Mellon University found that the majority of cars on U.S. roads are operating on tires inflated to only 80 percent of capacity. According to the website, fueleconomy.gov, inflating tires to their proper pressure can improve mileage by about 3.3 percent, whereas leaving them under-inflated can lower mileage by 0.4 percent for every one PSI drop in pressure of all four tires. That may not sound like much, but it means that the average person who drives 12,000 miles yearly on under-inflated tires uses about 144 extra gallons of gas, at a cost of $300-$500 a year. And each time one of those gallons of gas is burned, 20 pounds of carbon dioxide is adde