Paying attention to your tractor and combine tires can reap dividends

Wednesday, May 2, 2012

Choosing the right tires and the right tire pressure can reduce compaction, improve traction and add to operator comfort

by MIKE MULHERN

Buying a tractor or combine without carefully considering what tires the machine should ride on can cost time and fuel, and lead to increased compaction.

Most new equipment purchases come with a suite of tire options and buyers often go with the brand they're comfortable with. However, the tire makers themselves would rather you considered the matter in more detail.

Michael Vandel, marketing ag segment manager for Michelin North America, says farmers should not only know the weight of the machine being purchased, they should also figure out what pressure they want on their ground, and that's where tire differences apply.

When they're looking at combines, he says, farmers may consider everything but the tires because they view the machine as their office and they want to be comfortable. The question farmers should be asking is, "What is the front axle going to weigh on that machine when the hopper is full and what tire options are in the portfolio that will get me to a pressure of, say, 25 pounds per square inch (psi) in the front tires and 15 on the rear?"

Vandel says some farmers want no more than 15 psi across the field and some are comfortable with 25. The number is important because, if you reduce pressure, "you can reduce compaction, or at least spread it out further."

The reality is, Vandel says, "if you had one psi in a tire, you should have one psi of ground pressure."

Unfortunately, reduced tire pressure only reduces surface compaction. A study at the Penn State College of Agricultural Sciences Agricultural Research and Cooperative Extension found that "in completely flexible tires, surface contact pressure is similar to tire pressure." While the study showed reducing contact pressure "will cause less topsoil compaction" it does not eliminate the problem. "Lowering contact pressure will affect topsoil compaction but not subsoil compaction." That is determined by axle weight.

Tires for modern agriculture started with radial ones which came to North America in the 1970s.

The latest technologies have more to do with the inner workings of the tire. Michelin pioneered something called IF, meaning "improved flexion," which was introduced in Europe in 2004 and in North America in 2006. Other manufacturers have adopted the technology, along with the IF designation, and improvements have already been made. Now, Michelin offers tires with very high flexion and ultra-tech flexion.

Vandel says IF allows you to carry the same load per tire at a reduction in air pressure of 20 per cent. "The rolling circumference of the tire is the same, the amount of air the tire can handle is the same, even the tread pattern can be the same," he says. "The difference is the actual internal workings of the tire and how it is able to support that load minus 20 per cent of the air pressure."

The advantages are many. Setting aside cab suspension, the tires are the entire machine suspension system since there are no springs or shocks.

"We really have an air ride suspension in the tire. Lower air pressure should result in a lot more ride comfort," Vandel says. Lower air pressure also lengthens the footprint of the tire, so the weight of the machine is spread over a larger area, potentially reducing compaction.

Another benefit is an increase in "tractive capability." As you lengthen your footprint, you're transferring more of the horsepower of the engine to the ground. Better grip allows you to move forward using less energy.

Tom Rogers, director of marketing and sales for Bridgestone America's tire operations, which is part of the Firestone brand ag tire group, says "less slip, better traction means less time in the field" and less fuel burned.  

Firestone's version of IF is called Advanced Deflection Design. "It allows the tire to deflect further or run basically under-inflated," he says. The technology allows farmers to maintain the load they could carry using a standard tire and carry the same load at reduced pressure in the IF tire.

"I think the tire is a critical part of the performance of the tractor," Rogers says. Incorrectly matching loads to pressures "can take a 400-horsepower tractor and make it inefficient."

Raising the ante a bit, Michelin introduced a new combine tire to the North American market in February 2012 at farm machinery shows in Kentucky and Toronto.

The CerexBib tire will operate at pressures 30 per cent lower than standard tires while carrying the same load. Where width is an issue, either for truck transport or to be driven on the road, the new tire is 15 per cent narrower than standard tires designed for the same load.

If you're thinking of a tractor with more than 500 horsepower, Firestone just introduced the world's "largest ever agricultural radial" tire at the Agritechnica fair in Hanover, Germany, in November. The DT23, manufactured in the United States, is an IF850/75R42 tire. It weighs 510 kilograms, is seven feet six inches in diameter and has a load capacity of 9.5 tons at speeds of up to 50 kilometres an hour inflated at 23 psi. BF