There have been several instances of flat tires shortly after pit stops this year, and at least one crew chief has said lug nuts hitting the valve stems during tire changes have been the culprit. The shorter stems, it is believed, are less likely to be struck in the rush of a pit stop. "It's not a new design; we just shortened it as much as we can to allow the same core to be inside the valve stem," Greg Stucker, Director of Race Tire Sales for Goodyear, said.
"It just gets it out of the way a little bit more. It's not going to be a fix; but that's all we can do right now. It's a reaction to the people wanting us to do something so we did it as quickly as we could." NASCAR.com