Machinery Chatter

Where Tires Go to Die -- On Purpose

Dan Miller
By  Dan Miller , Progressive Farmer Senior Editor
The drum test applies loads up to 50,000 pounds on tires, while exposing them to rubber-aging ozone to simulate damage from sunlight. (Photo courtesy of Firestone)

I took a couple of days this week to visit Brad Harris. He is manager of the field engineering group at Firestone. He took me on a tour of the Firestone Farm Tire Test Center, at Columbiana, Ohio, about an hour northwest of Pittsburg.

It is here, on a 300-acre farm where Harvey Firestone grew up, that engineers validate tire designs and ever-improving materials. The tire test center is designed to torture Firestone's newest (and future) offerings. Here, tires go to die on purpose.

"Before a tire ends up on your farm, it's got to go through the Firestone farm first," Harris said. "We don't want customers to go down in the middle of the field." Especially when a tire costs $2,000 to $5,000.

The test center sports a pair of circular tracks paved with various surfaces to test tires mounted onto an overloaded and driverless tractor, the tractor tethered to the center of the circle. Tests here may run 1,600 hours to simulate extreme wear and tear. A drum test applies loads up to 50,000 pounds on tires -- while exposing them to rubber-aging ozone to simulate damage from sunlight. Plunger tests evaluate material strength and resistance to puncture. One building contains a very large, heavy steel cylinder in which tires are examined in a vacuum by lasers measuring minute variances in shape and wear not visible to the human eye.

Firestone's one-of-a-kind "Mean Machine" is a 30-ton beast that can exert 34,000 pounds of drawbar pull, enough to stop a tractor in its tracks. Loaded with an array of diagnostics, the Mean Machine mimics the resistance of the biggest and heaviest equipment in agriculture. It measures traction, drawbar pull, tire slip, rim slip, strength and durability.

Firestone can replicate five years of heavy use in three to four months to produce a tire that does what it supposed to do in the field and on the road.

Downtime is costly, said Harris, who farms himself. Firestone calculates that downtime during the season's optimal planting window (assuming an idle 16-row planter) can cost an operation $570 per hour due to yield loss. "A 15- to 30-minute check in the winter, when we're looking for something to do, can prevent costly downtime in the field," he said.

I asked Harris, what is the biggest threat to ag tires. He didn't hesitate. "The biggest killer of ag tires is stubble."

Corn and cotton stubble may be the worst, he said. Today's plants are engineered to be strong, to stand up against wind, and insect and disease damage. Stubble is harder than ever and tires can only resist so much. Tires faces two hazards from stubble. First is stubble piercing. That's when stubble punctures the tire, causing air loss. Second is stubble erosion. That occurs, as the name implies, over time. The stubble gradually wears through the tire treads to expose the radial cords.

There are ways to fend off stubble damage, Harris said. Drive at an angle to the row, not directly down the row, is one. Another is tread design. Firestone manufactures tires with a "stubble deflector" tread design -- the pattern pushes the stubble aside similar to a cowcatcher on a train.

A second tire killer, although one much slower than stubble puncture, is improper inflation. Tire pressure must match the load. "Guessing is wrong," Harris said, suggesting a $10 to $15 air pressure gauge can save many tires. Low pressure, without consideration for load will rapidly damage the sidewall of a tire.

Air pressure changes with the equipment used and by surface conditions -- for example, a muddy field versus a road surface at speeds up to 40 miles per hour. High clearance sprayers run on 17-inch tires inflated to 64 pounds per square inch (PSI) to carry 60,000 pounds. Larger planters will transfer 10,000 pounds to the rear of the tractor going from field to road.

"We need to know two things, tire size and the axle load," Harris said. "Then we can use inflation tables or the Firestone Tire Pressure Calculator ( Type in those numbers and you'll get the correct minimum inflation pressure to carry load."

Sometimes the operator will need several inflation calculations, Harris added. Carrying a three-point tillage tool. Duals on all year, or not. These change air pressure requirements. "In all those cases, we need to know how many tires and what those axle loads are," he said.

Harris and I talked about extending tire life. Firestone offers seven ideas:

1. Check tire pressure with a calibrated gauge and set the inflation pressure using a pressure calculator such as Firestone's Tire Pressure Calculator. Harris writes the correct inflation pressure in permanent marker near the inflation valve.

2. Check the tire sidewalls for cracks, cuts, and other damage. "Unlike a human cut, a tire doesn't heal itself," Harris said. "If you are seeing cords, it is time to look at getting a new tire."

3. Check tire treads and consider replacing if there is less than 20% left. "You'll lose traction in the field," he said. "The tries will slip and lose efficiency."

4. Check tire tread areas for stubble damage and exposed cords and replace tires with obvious damage.

5. Check ground contact area to make sure there is no gap between the lugs and the ground.

6. Check valve stems for cracks, corrosion, and debris. Make sure valve caps are clean and intact.

7. Check all nuts and bolts to ensure they are torqued correctly.

Harris added an eighth tip. As with all daily preventative maintenance, check the pressure of your tires daily.

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Dan Miller