2.2 somethings- it’s clear from observation that it can’t possibly be inches. In fact, it’s got to be something variable, perhaps based on a roll of the dice, or the ever fluctuating girth of Andy Cairns.
Otherwise, how can a 2.35 and 2.5 Swampthing be almost exactly the same size, and a 2.4 Advantage be bigger than a 2.35 Highroller (or, a 2.5 highroller actually measure 2.35, while a 2.7 highroller measures 2.5)?
I hear Alan Turing’s last great cryptoanalytic work was to calculate the relationship between bike tyre claimed sizes and reality, but Continental had him killed with a poisoned Mountain King. (or, some say, just a non-poisoned OEM spec Mountain King, and a slightly damp corner)