Understanding Tractor Wheel Sizes
Tractor tire sizes are indicated using both standard and metric formats.
The three formats are Standard (Imperial measurement, inches), Radial, and Metric (millimeters).
Standard tire sizes are the easier of the two measurements to read. An example is “16.9 – 30”. Here, “16.9” indicates the width of the tire in inches and “30” indicates the tire will fit a wheel that is 30 inches in diameter. The “-” indicates the tire is bias-ply design.
An example of tractor tire size expressed in Standard format would be “20.8-42”. The “20.8” means the tire is 20.8 inches wide and the “42” indicates the tire fits a 42-inch diameter wheel. The dash “-” indicates the tire construction is bias-ply (an "R" would be used if the tire were radial).
Metric Size Expression may look something like “520/85R42.” The “520” part means the tire is 520mm wide, “R” means it’s a radial tire, and “42” is the rim size expressed in inches, just like the standard method.
To measure wheel offset, there are a few steps. First, the wheel should be flat. Second, using a ruler or straightedge, measure the distance from the floor to the center of the wheel. Then, measure the distance from the floor to the edge of the wheel. If the second measurement is smaller than the first, the offset is positive. If it is larger, the offset is negative. Finally, subtract the smaller number from the larger number to get the offset.
It is important to check your existing tires and make sure your new tires will fit properly when changing your tractor tires. The largest manufacturers of farm tractor tires include Goodyear, Titan, Carlisle, and Advance.
If you need any further help or have any questions about service, tractors, implements, or anything else equipment-related, please contact your dealer, local mechanic, or call us at 602-734-9944. Please ask about our current new and used tractor supply.
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