18" tyres

[Lynn Eades]

David, For many years I was of the belief that the first number was the height of the side wall, ie 9.00 x 16 meaning an overall height 9+16+9 (total of 34 inches)
I was later told on this forum that the 9.00 was the foot print (width) and that it had nothing to do with the sidewall height.
As you have explained with the 100 percent aspect ratio, I was still right.

I do know that when the 70 series radials came out, that the size given (say 185 x 70 x 13) that the 185 related to the width, and that the height of the side wall was 70 % of the width.
I am not 100% convinced which is correct for the early cross plies.

[Richard Farrant]

Originally Posted by Lynn Eades

David, For many years I was of the belief that the first number was the height of the side wall, ie 9.00 x 16 meaning an overall height 9+16+9 (total of 34 inches)
I was later told on this forum that the 9.00 was the foot print (width) and that it had nothing to do with the sidewall height.
As you have explained with the 100 percent aspect ratio, I was still right.

I do know that when the 70 series radials came out, that the size given (say 185 x 70 x 13) that the 185 related to the width, and that the height of the side wall was 70 % of the width.
I am not 100% convinced which is correct for the early cross plies.

Think there were a few anomalies such as the 9.25-16 tyres as used on Humber 4x4 vehicles. Unavailable nowadays and replaced by 9.00-16 with is in fact larger diameter than a 9.25 !
Incidentally, on tyre sizes, the old crossply such as 11.00-20 has the "-" dash between tyre and rim size, but only uses the "x" cross on the older designations that used rim and overall diameters, eg 7x34