Bedford Tyres question, Pre WWII.

[Terance Wong]

I come across these two data. May I know what are their meanings please?
And how to convert them to some standard, such as 38 x 7 ins (965 x 178mm), please?

１）Bedford O series : Tyres 10.50 - 16

２）Bedford W series : Tyres Size - Front 6.50 x 20

Thanks

[Bruce Parker (RIP)]

Originally Posted by Terance Wong

I come across these two data. May I know what are their meanings please?
And how to convert them to some standard, such as 38 x 7 ins (965 x 178mm), please?

１）Bedford O series : Tyres 10.50 - 16

２）Bedford W series : Tyres Size - Front 6.50 x 20

Thanks

Those dimensions are in inches and refer to the width of the tire (or the rim) at the bead and the larger number is the diameter of the rim (or inner diameter of the tire). What it doesn't tell you is the overall outer diameter of the tire or its maximum actual width. Those could vary a little bit depending on the tire. There may be some chart I'm unaware of that correlates the rim width and diameter measurements you've shown to the actual tire dimensions.

[Terance Wong]

Originally Posted by Bruce Parker

Those dimensions are in inches and refer to the width of the tire (or the rim) at the bead and the larger number is the diameter of the rim (or inner diameter of the tire). What it doesn't tell you is the overall outer diameter of the tire or its maximum actual width. Those could vary a little bit depending on the tire. There may be some chart I'm unaware of that correlates the rim width and diameter measurements you've shown to the actual tire dimensions.

Thanks very much for your help. I have some basis idea now.

[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

[Terance Wong]

Thanks

[Ilian Filipov]

Hi Terance,
Here is one of the most useful things I've ever used for reference on all these British/Overseas tyres:


https://postimg.cc/S2dc3hSq

HTH
Cheers!

[Tony Smith]

Originally Posted by Bruce Parker

Those dimensions are in inches and refer to the width of the tire (or the rim) at the bead and the larger number is the diameter of the rim (or inner diameter of the tire).

No, they refer to the nominal width of the tyre at it's widest point (not at the tread or the bead), and do not refer to the rim width.