Tractor tires are going through a growth spurt. Up until six or seven years ago, the biggest farm tire you could buy for a tractor or combine was 6.8 ft. tall, categorized as Group 48. Now, tire manufacturers are producing even taller tires, called Group 49 and Group 50, with tire diameters of 7.2 ft. and 7.6 ft., respectively. In one roll, these tires can cover up to 22 ft. (see RCI chart below).

These extra-tall tires can be found on 4-wd tractors, grain carts, large combines and, most recently, high-hp row-crop tractors. This year, Case IH, New Holland and John Deere came out with high-hp row-crop tractors that can fit a Group 49 tire. The tires are available on other makes and models, too.

Tire makers say these larger-diameter tires are able to transfer more power to the ground and provide better traction than the next size down without increasing soil compaction as machines grow in size. This change in classes happens roughly every four to five years.

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“We are in a transition in equipment in terms of size, and we, as tire makers, have to keep up or stay ahead of it,” says Tom Rodgers, director of sales and marketing for Firestone agricultural tires. “Tractors keep getting bigger in terms of horsepower. Farmers can now get a 360-, 380-, 390-hp row-crop tractor, which 10 to 15 years ago was considered a big 4-wd. Group 49 tires give you more tire to carry the load and transfer additional horsepower at lower inflation pressures.”

Every size jump in equipment requires a corresponding jump in tire groupings, which are roughly separated by 4- to 5-in. increments, Rodgers says.

When you change the size of the tire, the geometry of the machine changes, too, he adds. “As you go up in tire size, equipment manufacturers must change the height of the axle and fender to make room for the bigger tires,” he says. “The machine will sit up higher, which will affect the height of a tractor’s 3-pt. hitch, the ground-engaging components on an implement or the feeder house of a combine. So growers will notice some differences on the machine, too, when they move to a different size of tire.”