Standard fitment for the MkIV was a 700-15 or 760-15 crossply tyre. A radial replacementfor this would be something like a 225/75R15.
Humber modernised the Super Snipe, a bit, in 1948. Continued improvement lead to the MkIV of 1952, when the styling of the Hawk models was adopted for the Super Snipe too.