March 2, 2011
If you thought you were a quasi expert on something as simple as tractor tires, maybe you should think again. There’s more to know than you might think, and it could affect your tractor efficiency and power when you pull into the field this spring.
Engineers at the AgTech Centre in Lethbridge, Alberta, have identified three areas where careful attention can improve tractor performance and affect traction power costs.
Not all farm tractors are optimally ballasted.
Not all tractor tires are correctly inflated for best tire performance.
Not all farmers effectively use their available horsepower.
Ballasting advice: “On ballasting, you want your tractor weight to be right for your operation and conditions,” says Reed Turner, consulting engineer at AgTech. “Manufacturers typically give a recommended weight range in pounds per horsepower. The recommendation for a 4WD can be from 85 to 125 lbs./engine horsepower.” Rubber track machines generally have different recommendations.
Turner says rubber tire tractors typically are most efficient pulling at levels around 40% of their total weight and track tractors at around 45%. “This means your tractor should weigh about 2.5 times the load it’s pulling,” he says.
“Commonly, 2WDs are ballasted to be 25% on the front and 75% on the rear. MFWD should have 40% on the front and 60% on the rear. Four-WDs are usually 55% on the front and 45% on the rear,” he says.
So should you ballast with fluid or cast iron? Turner says either will work. Fluid costs less and has a stiffening effect on tires that can be used to help control power hop, but can be a nuisance to move around or adjust. And it tends to corrode valve stems and rims. If you use fluid, make sure you spread it out equally in all the tires on a given axle.
Cast iron costs more and doesn’t do as much for power hop, but it’s easier to add and remove.
Get Tire Pressure Right
“Tire pressure is the easiest way to improve fuel efficiency and it’s the most often ignored,” says Turner.
To help you determine the correct inflation pressure, use manufacturers’ load-inflation tables.
According to Turner and research from AgTech, correctly inflated radial tires perform better and last longer than bias ply tires. However, radials do require more careful ballast and inflation pressure management than bias tires.
AgTech tests suggest that shallower lug angles show slightly better performance in good traction conditions and steeper lug angles show slightly better performance in poor traction conditions.
Tests also suggest that taller lugs perform slightly better in poor traction conditions and slightly worse in good traction conditions.
“To get optimum performance, run tires at the correct recommended inflation pressure for the weight they carry,” says Turner. “As low as possible always gives the best traction performance and the recommended pressure for a given weight as low as they can be.”
Size Tractor To The Job
AgTech tests suggest that many farmers do not use their available horsepower effectively because they’re not operating in the most efficient engine load range. “You can use a 200-hp tractor on a 100-hp job or a 100-hp tractor on a 200-hp job and you can probably make either work, but the result is lower efficiency and higher costs,” Turner says.
“An engine is in its sweet spot at or near its point of maximum power produced for fuel used,” he says. “Remember that you are not lugging an engine when you load it enough to pull it down on its torque or power curve to the area around rated speed.”
When the engine is at its maximum efficiency range, then make sure traction is part of the equation. Turner reports that rubber tires provide their optimum power delivery at around 10% slip, rubber tracks at around 5%.
“If the slip is much below 8% for tires or 3% for tracks, and the engine is appropriately loaded at a reasonable ground speed, the tractor is probably too heavy,” he explains. “If the slip is much above 12% for tires or 7% for tracks, the tractor is probably too light.”
About the Author(s)
Greg grew up on a diversified crop and cattle operation in South Dakota, and has 22 years of experience covering the farming and livestock business. A graduate of South Dakota State University, he served as managing editor of BEEF magazine for five years, previously working for Farm Journal, Successful Farming and Feedlot Management magazines, as well as having served as an account executive with the Colle&McVoy advertising agency. Greg is the recipient of numerous writing and photography honors.
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