History of 10.50-16 tyres

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As those old vehicles were superseded by modern types wanting wider profile tyres without increase in rolling diameter we started to see the width-height relationship change with percentage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

[Tony Smith]

Originally Posted by Lang

Lauren

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

Lang

Almost universally, Radial tyres with R in the size are 78% aspect ratio.

[Lang]

Tony

Where abouts is the reference to that. I can't find it in the Tyre and Rim Association manual.

Not saying you are wrong but the manual says the difference between 7.50x16 and 7.50R16 is only 4mm overall height (within normal manufacturing leeway). Everything I can find says the old tyre is 100 aspect ratio making the "R" tyre the same.

Maybe some of the other sizes went with the 78%?

Of course that stand alone "R" measurement only applied to tyres in the transition period between bias and radial construction - you can still find a few sizes so marked being produced for older applications. I think the 8.25R16 is still in use with the little 3-5 ton Isuzus and Mitsubish/Hinos.

All tyres have "R" in the size now but it is preceded by the aspect ratio so has nothing to do with size eg 185/65R14

Lang

PS

I just measured the 8.25R16 tyres on my OKA. Exactly 8.25 wide and 8.25 high giving an aspect ratio of 100.

PPS

I went looking and found a 7.50R16 M&S pattern on a wheel. Measured exactly 7.50 X 7.50. Measured the 7.50X16 Military ND on my 1/2 ton Dodge - exactly 7.50 x 7.50

[gjamo]

There appears to be seveal alternatives here.

https://www.vrakking-tires.com/14-16...tegory=14&n=75

[Lang]

This seems to sum it up for truck tyres.

Tube type tyres, whether radial or bias have a height close to width (98%) What I found with my two measured examples above.

Tubeless radial tyres unless profile specified have an 88% height.

Aspect Ratios
Truck tires sizes starting in 8, 9, 10, 11 and 12 are standard profile tubeless with the tire body width in inches. Standard profile tires have an aspect ratio of 88 percent. The height of the tire from rim to tread will be 88 percent of the width. An 11R22.5 tire will be approximately 11 inches wide and 9.5 inches high. Low profile tires show the width in millimeters and the aspect ratio. A 275/80R22.5 tire is 275 millimeters wide 220 millimeters high. Typical low aspect truck tire ratios are 70 percent, 75 percent and 80 percent. Tube-type tires are given widths as 9.00, 10.00 or 11.00, as in 1000R20, pronounced "ten hundred R twenty." Tires requiring inner tubes have an aspect ratio of 98 percent.