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Tires versus tracks: separating fact from fiction

Experts weigh in on tires, tracks and minimizing soil compaction

If conversation slows in a room full of farmers, three little words can ramp up a rowdy discussion: tracks or tires? Tracks have gained loads of attention and growing popularity over the past decade. However, does science back up their many supposed benefits, especially when it comes to minimizing soil compaction?

Partial fact: Tracks produce less contact pressure on the ground

It’s true that across North American fields today, tracks are generally doing a better job of distributing the weight of equipment across a wider surface area, resulting in less compaction. However, that’s not because the technology of tracks is so much better, it’s because farmers who rely on tires may not be managing their tires correctly.

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“Compaction is based on both tire p.s.i. and axle load,” says Jodi DeJong-Hughes, a regional extension educator with the University of Minnesota.

From a pure axle load perspective, tracked machines are generally heavier than their wheeled counterparts. However, from a pounds per square inch (p.s.i.) perspective, tracked machines have a fixed p.s.i., whereas wheeled machines need to be checked often for the manufacturer’s recommended p.s.i.

“There is a lot of hype about tracks and tires,” says Marla Riekman, a soil management specialist with Manitoba Agriculture. “If tires are run at their rates of pressure for field work, they typically are equal to tracks in terms of the total pressure that is being exerted on the soil causing compaction.”

Unfortunately, the majority of farmers overinflate their tires, resulting in unnecessary compaction. By comparison, tracks offer the significant benefit of eliminating that form of operator error.

“One guy told me: ‘Where I plant behind my tractor with tracks, the plants do better than tires.’ I asked: ‘What is the p.s.i. of those tires?’ He didn’t know. He can’t make a comparison because if his tires were overinflated to 30 p.s.i. and his tracks were at 15 p.s.i. (ground pressure), that’s not comparing the same thing,” says DeJong-Hughes.

According to research conducted by Firestone Ag and published in the journals of the American Society of Agricultural and Biological Engineers, tires inflated to less than 20 p.s.i. transmit less contact pressure to the soil than tracks. Tires inflated to between 20 and 35 p.s.i. produced comparable pressure to track systems. Tires inflated over 35 p.s.i. resulted in the track system offering lower contact pressure than the tires.

“One of the biggest bangs for your buck is going up to a larger tire so you can go to a lower p.s.i.,” says DeJong-Hughes.

Fiction: Track = no compaction

If you send two tractors across a field — one with tracks and the other with tires — track advocates will point out that the tires create significantly more rutting than tracks virtually every time. While that observation is true, the difference in rutting isn’t related to the level of floatation or compaction occurring. Instead, it’s related to the difference between how tracks and tires propel machines. A wheel pushes the machine forward, creating a wave of displaced soil ahead of each wheel and a rut behind. Tracks, on the other hand, dig into the ground and pull the machine forward, mostly leaving soil in place.

“There’s a big misconception that no ruts mean no compaction. If you have a track and you think you’re not compacting, think again. It’s not a magic bullet,” says DeJong-Hughes.

Partial fact: Tracks spread the equipment’s weight over a wider surface area

A track’s footprint looks much bigger than a tire’s, leading farmers to assume that weight is distributed across the entire surface. That assumption is not, in fact, always true.

“If the track is not the same size as the carriage — say the track is three feet wide and the carriage is only two — you’ll have six inches of track hanging off each side. That track is pretty stiff rubber so it’ll be carrying some weight, but not as much as you might think. You might calculate the track at an average of four or five p.s.i. but that’s not completely accurate: under the dolly wheels are probably more like 15, especially since the rocking of the tractor changes weight distribution,” says DeJong-Hughes.

Fiction: Track produce consistent contact pressure on the ground

Because a large surface area is always in contact with the ground, tracks appear to provide a very even distribution of weight. That’s not really the case. In fact, pressure is highest under the drive wheel and significantly lower between the dolly wheels. “Farmers need to keep in mind that soil is compacted by the highest pressure point,” says DeJong-Hughes. “There’s surprisingly inconsistent pressure along a track.”

Fact: Track and tire systems each offer pros and cons

Tracks cost more, both in upfront cost and in ongoing maintenance. While tires have no moving parts, tracks have many. Tracks also require more horsepower to operate, which translates to higher fuel consumption. However, tracks offer the big advantage of better traction and less slippage, especially in wet soil. And, smaller tracked machines offer more pull than machines with tires because the tracks grip better.

Ultimately, farmers need to determine what’s right for their operations. Regardless of the option they choose, they should make sure they understand the realities of the technology and set the equipment up for success.

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