BOSTON -- In the world of car tires, there may be a change in the air. It seems air might not be the best thing to pump into them.

NewsCenter 5's Jim Boyd reported Thursday that those who deal with cars everyday said one of the key ways motorists can save gas is by paying attention to the rubber that hits the road.

"Forty percent of the tires that are on the road are underinflated, and that kills the gas mileage," auto technician Jim Lahaise said.

Lahaise said that motorists could check inside the driver's door for information on the proper tire pressure for maximum efficiency of their automobile.

Motorists will soon have the benefit of a new option -- inflating their tires with nitrogen.

Service manager Gene Robbins said that it's all in the science.

"With nitrogen, the molecules are bigger. They won't escape out of the pores of the tire," Robbins said. "The reason you get the fuel economy is because you are always going to maintain consistent tire pressure."

Robbins said that using nitrogen could save in other ways than fuel economy.

"It's going to prolong the tire. You'll get maximum tire life. It might even exceed what the manufacturer recommends," Robbins said.

Also key to a smooth running car is making sure that the engine air filter is clean.

"Anything that restricts the air flow is going to bring down the fuel economy," Lahaise said.

Robbins said that he expects to begin providing nitrogen for consumer tires around June 1. But considering the cost of the new machinery, he said he regrets for the first time in history he'll have to charge customers to fill their tires not with air, but with nitrogen. It will cost about $8 per tire.