Tire Size Conversion Chart

Two versions of numeric tire sizes were used as original equipment on vehicles between 1949 and 1970.

The early numeric tires had the equivalent of a 90-series aspect ratio, while later tires offered a "lower"

profile equivalent to a 80-series. These tires typically featured tread widths ranging from 3.5" for the

smallest 13" rim diameter tires to about 5.5" for the largest 15" rim diameter tires.

To convert Numeric sizes to today's P-metric sizes, it is important to remember that early cars were not only

equipped with narrow tires, they were equipped with narrow wheels as well. In most cases, numeric tires

should be replaced with today's 80- or 75-series sized tires. This is especially important if the original

Alpha numeric tire sizes were introduced as original equipment in the late 60's and became widely used in

the early 70's. These tires were identified with a letter which indicated the tire's load capacity, followed by a

"R" if radial ply construction, the tire's aspect ratio and wheel diameter. So while G78-15 (28.01"), G70-15

(27.5") and G60-15 (26.4") sized tires are all rated to carry the same load, their different aspect ratios

resulted in tires with the overall diameters indicated above.

To convert Alpha Numeric tires to P-metric sized tires, it is important to identify the original tire's aspect

ratio. The 78-series Alpha Numeric tires should be replaced with today's 80-, or 75 series tires. If the

vehicle was equipped with the low profile 70-, 60- or 50-series sizes, the P-metric substitution should be

selected from the P-metric size column that offers the equivalent aspect ratio as the existing tire.

For example: The 1970 Chevrolet Camaro Z-28 F60-15 would be replaced with a P235/60R15 (selected

1964

1970

NUMERIC

"80"-Series

Series "82"-Series

80-, 75-

series 70-series 65-series 60-series 50-series