How do I Convert an F78-14 Tire Size?

by Tim Plaehn
itstillruns article image
classic car image by itsallgood from

In the 1960s and 1970s, the tires installed by the car manufacturer had a letter designation and aspect ratio, according to the Tire Rack website. The letter indicated both the size and load capacity. Tires of the era were bias ply, with tire bodies constructed of cloth belts laid at a angle or bias. Modern tires are radial construction with the belts laid perpendicular to the rolling directing of a tire. Bias and radial tires handle and wear significantly different from each other. Converting the size can be done to a currently used bias ply size or a modern radial tire size.

Step 1

Locate an online tire size conversion chart. Classic car websites often have a chart showing the different tire sizes and their measurements (see Resources).

Step 2

Find the chart that gives the actual measurement for an F78-14 tire. Some charts show comparable sizes, but it is better to get the actual measurements first. An F78-14 tire has a diameter of 26.5 inches and goes on a 5.5-inch wide rim.

Step 3

Look up the comparable modern tire size using the tire comparison charts. According to the charts metric tires sizes, 200/70-14 and 195/0-14 are the equivalent metric sizes for F78-14.

Step 4

Verify the modern size tires will substitute by looking up the actual tire size and recommended rim width. For example, a comparable modern tire size would be 205/70R14. This size tire will fit on a five- to seven-inch wide rim and is 25.4 inches in diameter. Moving up a size to 215/70R14 gives a tire 26.9 inches in diameter.

More Articles

article divider