Allis G rear tire size?

Allis G original tire size was 6 x 30; todays tire size is 7.2 x 30.  This original size was still listed in April 26, 1951 dealers "Agricultural Price List Book".   What was the reason for this later size change?    And when did this change occur?

Tire sizes didn't change much, the numbers did. The old tire sizes were rim size for width. Later the number was changed too the maximum width of the tire. 7.2 is the same size tire as 6. The tire manufacturing association that set the standard arranged that most of the time they didn't use the same number for a tire width as had been used for a rim width usually keeping rim widths hole numbers and tire widths decimal numbers with a small fraction like the .2 in 7.2. I found a library collection of the tire standards at the ISU library and made note of the changes one time, but I don't remember the year the change was first an option or the year when they decided it was manditory. There probably were several years of overlap.

Later tires where changed again, especially road tires, to showing width and ratio of height to width. Most often used for radial tires with the width in millimeters instead of inches.

Gerald J.

6.2 is the new label for something smaller than 6, probably 5 x 30. 7.2 is the new label for the old 6x30.

Gerald J.