Always wondered why any land speed racing organization made this a ruling along with metal valve stems. Well, after getting the turbo flatty built and on it's maiden run I ran it up to 70mph and in a slight curve the front end suddenly had a terrible shimmy. I thought the front axle came loose. The cause? I didn't have a valve stem cap and the valve core broke in half and blew out loosing all air fast. If a cap was in place this would never of been a safety problem. Even it the core was defective the cap would of held the air.