Tires made for harvesting

LOUISVILLE, Ken. — Farm power unit tires are asked to do many things.

They provide traction for pulling and weight dispersion without compaction — both without excessive field disturbance. And, if they’re on a combine, they have to be able to take a load of up to 30,000 pounds coming and going with each hopper load.

Tractors only see a variable fuel load, and the tires that are found on most combines were designed for tractors.

At February’s National Farm Machinery Show in Louisville, Kentucky, Michelin released its first ultra-flexible tire specifically for combines and forage harvesters.

The CerexBib, as the new rubber is dubbed, is available in IF and VF ratings, meaning it can take the same load as a standard tire, but at either 20 percent or 40 percent less inflation. That results in tires that can maintain a larger surface area than a standard tire while carrying the same load. The lower the pressure and the bigger the surface, the less compaction there is in the soil. The IFs go on the front, VFs on the back.

“For the most part it will mean that our combine tire, the CerexBib, will carry about 40 percent less (air) pressure than most other tires that are on combines today,” said Michael Vandel of Michelin North America Ag Tires.

The front IF rated tires can take a cyclic field operation, the technical phrase used to describe what happens to a tire that gets loaded and unloaded in the field, while maintaining all of its design qualities and without requiring increases or decreases in pressure. In this case, it’s up to 86 percent in load variation.

“Those back tires are often overlooked. They get the biggest load of all on the combine. These smaller tires get their share of what is in the hopper, but what happens when you drop that header off. All that weight is gone in front, shifting the load of the engine and threshing to the back of the machine.

“Typically you have them overinflated for the field or underinflated for the road. We’ve fixed that,” he said.

The rear tires are VF rated and come as a 58 inch tall, 20 inch wide 520/80R26 or a 59 inch tall, 24 inch wide 620/70R26.

The IF rated front tires are available in four sizes. There are three 800s — a 65R32, a 70R32 and a 70R38 — and a 680/85R32.

The biggest has a diameter of nearly 81 inches and is about 31 inches across.

The extra deep lugs are swept back at a 45 degree angle and splayed at the bottom, adding additional rubber. Added rubber can also be found in the shoulders and bead areas. This combination allows the tires to carry the additional load at the lower pressures.

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