IMPORTANT: Avoid excessive drive train wear. Do not mix worn and new tires, bias and radial, or tires of different diameters. Do not use R2 tires in combination with R1.

With the tire industry converting to metric designations, there are many new terms which can be confusing. To simplify things, tires are placed into groups by their Rolling Circumference Index (RCI) . Rolling circumference is the distance a tire travels in one revolution. Tires within a group, regardless of rim size, are the same or nearly the same height. Knowing and understanding RCI and group sizes makes choosing front and rear tire combinations easier.

RCI is important for proper tractor setup. Since front tires are smaller than rear tires, front tires have to rotate faster to cover the same distance as the rear. Therefore it is important to select the correct size to optimize efficiency and ensure longer tire life.

The front tire must be from a group that is five group sizes smaller than the rear tire group. For example, if the rear tires are group 47, then the front tires must be group 42. The rim size is of no consequence. Different rim-size tires such as 18.4R46 and 20.8R42 have the same rolling circumference group, which is 47. Tire sizes are found in the following tables.

If you have any questions or need assistance in choosing the correct combination, see your John Deere dealer.

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