[Lang]

Lauren

The "R" stands for RADIAL and is not a size indicator.

For instance, the very common 7.50x16 used on Landrovers, Landcruisers etc for 50 years was a 100 profile (height equals width) tyre.

The world moved on, so for about 20 years in the 70/80 period they designed a new radial construction tyre to match equal height and width of the old bias construction. They called it 7.50R16

As those old vehicles were superseded by modern types wanting wider profile tyres without increase in rolling diameter we started to see the width-height relationship change with percentage profile measurements.

For those old vehicles still operating, they now have to go to the 235/85x16 which is the same height as the old 7.50x16. The difference is that it is 235mm (instead of 7 1/2 now about 9 1/2 inches) wide but, only 85% of that in height, to achieve the same diameter as the old tyre.

All the various commercial tyres (and most car tyres too)of whatever size went through that progressive change.

Lang