in any case the industry says there's no evidence that aged tires are a danger but the new federal investigation by the national transportation safety board aims to find that out for sure. brian ross, abc news, new york. >> scary stuff. >> this is the biggest problem. this process of aging happens naturally obviously. whether it is being driven, it's on a shelf, it's in the backyard that somebody is going to put back on their tire or being pristinely kept in a museum, it is aging and a dangerous tire after six years. >> in 1973, the average tread life of a passenger car tire, 24,000 miles thanks to better rubber processing. now it is 100,000 miles. the tires themselves have improved but you definitely have to keep this in mind. >> yeah. and it is up to the consumer. you go to a tire shop and there are tens of hundreds of tires in these shops and they have been there a long time. >> at least we know how to do it. the week and year. in hotter climates like texas, florida, georgia, mexico, new mexico, you have to be extra