Tyre size increase offers more choice

About six or seven years ago, the biggest tractor or combine tyre you could buy was 2m tall, categorised as Group 48.

But now tractor tyres are going through a growth spurt.

Tyre manufacturers are producing taller tyres, called Group 49 and Group 50, with tyre diameters of 2.2m and 2.3m, respectively. In one roll, these tyres can cover up to 6.7m.

These extra-tall tyres can be found on four-wheel-drive tractors, grain carts, large combines and, most recently, high-horsepower row-crop tractors.

This year, Case IH, New Holland and John Deere came out with high-horsepower row-crop tractors that can fit a Group 49 tyre.

The tyres are available on other makes and models as well.

Tyre makers say these larger-diameter tyres 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.

"We are in a transition in equipment in terms of size and we, as tyre makers, have to keep up or stay ahead of it," Firestone Agricultural Tyres sales and marketing director Tom Rodgers said.

"Tractors keep getting bigger in terms of horsepower.

"Farmers can now get a 360, 380 or 390 horsepower row-crop tractor, which 10 to 15 years ago was considered a big four-wheel-drive.

"Group 49 tyres give you more tyre to carry the load and transfer additional horsepower at lower inflation pressures."

Every size jump in equipment requires a corresponding jump in tyre groupings, which are roughly separated by 10cm to 12cm increments, Rodgers said.

When you change the size of the tyre, the geometry of the machine changes, too, he added.

"As you go up in tyre size, equipment manufacturers must change the height of the axle and fender to make room for the bigger tyres," he said.

"The machine will sit up higher, which will affect the height of a tractor's three-point 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 tyre."

Titan and Goodyear Farm Tyres agricultural products manager Scott Sloan said there were benefits to running a taller tyre - the biggest being load capacity.

"A Group 49 tyre is going to be able to better handle the load of today's high-horsepower tractors better than a Group 48 tyre of the same width," he said.

"By being able to handle the load without raising inflation pressures, the grower can expect less ground-bearing pressure, which leads to better flotation and less soil compaction."

Mr Sloan said Goodyear Farm Tyres was one of the first companies to offer a Group 49 tractor and combine tyre in early 2000, and now offered Group 50 and Group 51 tyres as well.

"For row-crop applications, Goodyear offers Group 49 tyres in section widths ranging as low as 480mm, as well as tyres as large as Group 51 in section widths as low as 320mm."

Whether a farmer should go with a larger tyre size will depend on the load, application and design of the machine, tyre companies advise.

Older-model tractors are not designed to fit the new size categories because they are offered as an option on new-model machines.

The larger tyres are available in both standard and increased flexion versions.

IF tyres have more flexibility in the sidewalls to allow for more air and a bigger tyre footprint.

Farmers should work with their dealer to determine the best size and type.

The bottom line for farmers is the larger sizes will give them more options during the tyre-buying process.

"For new equipment purchases, a grower may get the opportunity to specify a Group 49 tyre as an upgrade versus a shorter tyre," Mr Sloan said.

"It's important that the grower looks at the load-carrying capacity and inflation pressure benefits that come with running a taller tyre.

"It's also important to look ahead to the future, knowing that any replacement tyres will need to have the same size of rim."

These larger tyres will cost more than the mainstay Group 48 because of the additional rubber and materials.

But tyre makers say the return on investment will come through better traction and less soil compaction due to the bigger footprint.

Whether a farmer should go with a larger tyre size will depend on the load, application and design of the machine