Bedford Tyres question, Pre WWII.

[David Herbert]

Terance,
You will be familiar with modern tyres being designated like this: 255 55 16. In this case the tyre has a nominal width of 255mm, the extra radius beyond the inner diameter of the tyre is 55% (known as the 'profile') of 255mm - ie. 140mm, and the inner diameter that fits the rim is 16 inches. Before radial tyres it was normal for the width to be in inches too and the profile of 1960's car tyres was generally 80%, though that was rarely marked on the tyre. In the 1940's tyres were almost always 100% profile so the width was normally also the height (extra radius). Thus a 7.00 - 20 tyre was 7 + 20 + 7 = 34 inches diameter. Pre WW2 that same tyre would have been designated 34 x 7 but it was exactly the same.
If the tyre were marked 7.50 - 20 it would be 0.5 inch wider than a 7.00 - 20 and an inch larger in overall diameter. The one common anomaly is 9.25 - 16 British WW2 tyres which are about the same width but significantly lower profile than 9.00 - 16. At that time no one had thought to have a separate profile designation.
So your example of a 38 x 7 tyre would have a width and height of 7 inches, a total diameter of 38 inches and fit a 24 inch wheel. It was a common size on fire engines and buses.

David