1956 was the first year for the 22.5 wheels on Chevy trucks.. A lot of people did not trust the tubeless tires as much as the tried and true tube type so, there were still a lot with the 20" tube tires sold as well. My 58 had 22.5 tubeless on it, except for one rear wheel, they had swapped both on that side for 20" (widow-makers). They probably needed new tires and had those sitting in the shop or on another truck that was not in use.
