18" tyres

[motto]

To explain a little further. The first group of numbers i.e. 10.50 refers to the nominal width of the tyre in inches. In this case ten and a half.
Around WW2 this would also give a good idea of the height of the tyre as most of them seem to have a 100 percent aspect ratio. By that I mean the distance from the inner diameter of the bead to the tread surface would also be close to ten and a half inches.
None of this relates to the rim width which would probably be around seven inches across the inside of the flanges.
The second group of numbers relate to wheel diameter. A 10.50-18 tyre would go on an eighteen inch wheel so the hole in the middle of the tyre would be 18 inches across.
By this reckoning a 7.50-20 tyre would be about 35 inches in overall diameter. 7.5"+20"+7.5"=35" and this works out pretty close although there is some variation between brands. Some makers back then actually gave the tyre outside diameter as part of its identity i.e. 7x34 although that wasn't general practise and fell by the wayside.

David

The foregoing is only my observation and open to correction or addition.