The original YA saloon and YT tourer had 16 inch wheels, and were fited with 525-16 crossply tyres. The later YB saloon moved to 15 inch wheels and a 550-15, or 590-15 sized crossply tyre.
MG's postwar saloon/tourer was a prewar design, and used the engines from the T-series sportscars. Not hugely fast or modern, they were good value and full of character.