In an earlier contribution to this discussion,
Osprey wrote:

Been trying to understand tyre markings on my trailer tyres.
It is marked as 205 75 R14

That should mean (I think) rim diam is 14", height of tyre is 75mm and
width is 205mm.

Form this you would assume overall diam of Tyre would be 14" (i.e.
355mm) plus 2 x 75mm so overall width of 505mm
Yest if I measure it the overall width is 635mm significantly
different.

Anybody know why the discrepancy?

As others have said, the 75 refers to the aspect ratio as a percentage. So
the 'height' of the tyre is 75% of 205 = 153.75

So the overall diameter is (14 x 25.4) + (153.75 x 2) = 663 mm

Not quite the 635 which you measured, but a lot closer than 505!

For tyre markings in general, see
http://www.ntta.co.uk/law/trailers/tyres.htm
--
Cheers,
Roger
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