The modern tyre designations as you illustrate Lynn follow a different format. I believe the first group of numbers is the nominal width in millimetres i.e. 185 or 205 etc. The carry over is that they still give the wheel diameter in inches.
Perhaps the reason for the 9.25 designation Richard was to differentiate the Humber tyre from something similar and was not meant to be a true indicator of size.
Grant, you've rung a bell with your mention of high pressure tyres. I think they were what my Dad referred to as 'hardwalls'. Dad grew up in the 1920s, was a vehicle enthusiast all his life and was familiar with all the old stuff. He passed away a couple of years ago at the age of 93. I sure do miss him.
David
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Hell no! I'm not that old!
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