PALM DESERT, Calif. -

Gary Sigler's boat trailer tires looked brand new when one of them suddenly blew out.

"It sits in the garage most of the year where you wouldn't think the rubber would go bad, but sure enough," Sigler said. 

The barely-used tires were seven years old, which a new investigation into tire safety shows is too old. 

"Here in the Coachella Valley, I tell my customers five or six years at the most," said Marty Hart, owner of Marty's Tires Plus in Palm Desert.

Hart told us some of his customers wait too long to replace their tires. He says many people don't realize in the desert heat, tires can actually age faster, posing a dangerous risk on the road.

"Over a period of time the tires literally dry rot, just from sitting. So they lose their integrity and their strength," Hart said.

The other issue: knowing when your tires got made. To check the age of your tires you must look at the side wall of the tire.
There's a 12-digit Department of Transportation code and the last four digits are the week and year the tire was manufactured.

"It's counterintuitive. The tire industry says it's convenient for them and that it's not that difficult to find, but most people I talked to had no idea that number was there," said Brian Ross, ABC News' Chief Investigative Correspondent.

We found the same reactions here in the valley.

"Very confusing.  I'm glad I have Marty to help me because it's something I need to pay attention to," said Willena Martin of Palm Desert.

Currently, there's no law or industry standard preventing the sale of aged tires. And, because of strong lobbying by the tire industry, proposals in eight states to require inspection of tire age went flat.