John,
Chevrolet first offered 22.5" tubeless tires on 1956 model trucks which were offered for sale in late 1955. I have tons of info confirming this, such as...1956 Service Bulletins, 1956 Service Selector book, 1956 Specification book, Parts Books and a 1955 Second Series Specification book showing only 20" tube type as being offered.
Trust me on this one

Mike B
