[Steve Ciccalone]

Changes to tires and tubes were generally dictated by the Tire and Rim Association (they issued the TR numbers to the various stem manufacturers for various applications), established in 1908 to help ensure and promote industry wide standardization like SAE. Ford used metal stems through 1934. The vulcanized integral rubber coated stem tubes were undoudtedly not proven or readily available until 1935. Use of these tubes saved several production steps and would have been employed earlier if they were reliable in my opinion.