Tire Rack.com

Tire Size Conversion Chart

Lea esta página en español

While today's P-metric passenger tire sizes have existed since the early 1980s, restoring classic muscle cars and ponycars has kept yesterday's Numeric and Alpha Numeric tires from disappearing. This chart is intended to help you determine their equivalent P-metric tire sizes.

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 an 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 wheels are to be used. Today's lower profile sizes will usually result in too wide a tire with too much gap between the wheelwell opening and the top of the tire.

For example: The 1965 Ford Mustang's 6.95-14 would be replaced with a P185/75R14.

Tire SizeOverall DiameterSection WidthLoad Capacity
6.95-1425.3"7.0"1230 lbs @ 32 psi
P185/75R1425.0"7.2"1290 lbs @ 35 psi

Alpha numeric tire sizes were introduced as Original Equipment in the late 60s and became widely used in the early 70s. These tires were identified with a letter which indicated the tire's load capacity, followed by an "R" if radial ply construction, the tire's aspect ratio and wheel diameter.

So while G78-15, G70-15 and G60-15 sized tires are all rated to carry the same maximum load, their different aspect ratios resulted in tires with the overall diameters indicated below.

Tire SizeOverall DiameterSection WidthLoad Capacity
G78-1528.0"8.4"1,620 lbs @ 32 psi
G70-1527.5"8.6"1,620 lbs @ 32 psi
G60-1526.4"9.7"1,620 lbs @ 32 psi

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 replaced with a P235/60R15 (selected from the P-metric 60-series column).

Tire SizeOverall DiameterSection WidthLoad Capacity
FR60-1525.9"9.4"1500 lbs @ 32 psi
P235/60R1526.1"9.3"1642 lbs @ 35 psi

This chart can help you determine today’s closest equivalent Euro-metric or P-metric tire sizes for popular 1949 through 1980 tire sizes.

Most Popular Links

Air Pressure - Correct, Underinflated and Overinflated
Air Pressure vs. Dry Performance
Air Pressure vs. Wet Performance
Air Pressure, Temperature Fluctuations
Air Pressure/Load Adjustment for High Speed Driving
Air Pressure: When and How to Set
Breaking In Your Tires
Calculating Tire Dimensions
Checking Tire Inflation Pressure
Determining the Age of a Tire
Diameter Comparison of Light Truck Tire Sizes
How Do I Compare Price vs. Value?
How to Read Speed Rating, Load Index & Service Descriptions
Load Range/Ply Rating Identification
Match Mounting to Enhance Tire & Wheel Uniformity
Load Reduction of Euro- and P-Metric Tires on Light Trucks
Measuring Tire Tread Depth with a Coin
Mounting and Balancing
P-Metric and Euro Metric Tire Sizing
Run-Flat Tires
Selecting the Right Tires
Sidewall Markings
Specific Mileage Warranties
The Plus Concept
Tire & Wheel Owner's Manual
Tire & Wheel Package Installation Instructions
Tire & Wheel Package Ride Uniformity Confirmation
Tire Pressure Monitoring Systems
Tire Rotation
Tire Size Conversion Chart
Tire Size Information
Tire Warranties
Uniform Tire Quality Grade (UTQG) Standards
Where to Install New Pairs of Tires?


Want to stay on the inside track?
Sign up for our emails today!