Help Me Convert!
Former Vendor
Joined: May 2000
Posts: 4,776
Likes: 147
From: 877-522-8473 ext. 4362
St. Jude Donor '11-'12
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 G78-14 (27.01"), G70-14 (26.5") and G60-14 (25.4") 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 from the P-metric 60-series column).
or to make it a little more simple your tires would be:
G78-14 = 215/75-14 / 26.7"
G70-14 = 225/70-14 / 26.4"
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 from the P-metric 60-series column).
or to make it a little more simple your tires would be:
G78-14 = 215/75-14 / 26.7"
G70-14 = 225/70-14 / 26.4"
