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Reducing Radial Tractor Tire Pressure Can Improve Performance and Reduce Soil Compaction

Letting some air out of radial tires is an excellent way to improve performance and efficiency of your tractor and reduce soil compaction, according to a North Dakota State University agricultural engineer.

Tire manufacturers reduced radial tire pressure recommendations in 1992, notes Vern Hofman of the NDSU Extension Service. Current recommendations call for tire pressures as low as 6 pounds per square inch as long as the load-carrying capacity of the tire isn't exceeded. Previously, recommended tire pressure rates were 15 to 20 pounds per square inch. Lower pressures are possible because radial tire construction provides greater strength and flexibility than bias ply tires.

"When radials first came out, we didn't really know their capabilities so we just recommended the same tire pressures as bias ply tires," Hofman explains. "With more research, tire manufacturers were able to reduce the tire pressure."

The research shows that correctly adjusted tire pressure can reduce tire slippage by as much as 20 percent. Reducing tire pressure distributes the weight of the tractor over more soil area due to tire flexing. Also, lower tire pressure reduces soil compaction as the pressure in the tire is very closely related to the force on the soil surface. If a producer has a soil compaction problem, lower tire pressure can reduce the effect.

"More tire contact with the soil means better traction," Hofman says, "and that means more work done by the farmer in the same amount of time."

Reduced slippage can extend tire life and reduce fuel consumption. Reducing the pressure also can prevent "tractor hop," the chattering motion that makes tractors act like bucking broncos. "When a tractor is pulling hard, tires tend to break loose from the soil and then grab again," explains Hofman. "The improved traction from reduced tire pressure will reduce that effect."

Hofman also recommends reducing tire fluid to no more than one-fourth to one-third of the tire volume. Fluid reduces the flexing of tires. If fluid amounts are reduced, producers may have to replace the weight lost by adding cast iron weights, Hofman says.

Tire slippage should range from 8 to 12 percent. This needs to be measured in the field while pulling a good load behind the tractor. To adjust tire pressure properly, you need to know how much load each tire is carrying. This information is available from tractor manufacturers or by weighing the tractor.

Once you know the tire loads, refer to tire load and inflation tables from tire manufacturers to determine the correct inflation pressure.

"I think people are hesitant to reduce tire pressures because they see so much flexing on the sidewalls," Hofman says. "They figure that all the flexing will ruin their tires." Tire damage from sidewall flexing was common in bias-type tires. Radial tires are built to flex like radial tires used on cars and pickups. You can reduce tire pressure in radial tires without causing any problems, Hofman says, as long as the load-carrying capacity of the tire isn't exceeded.

But it is critical that low tire pressures are accurate, Hofman says. "Do not allow the pressure to drop below the recommended level." Tire pressures must be checked regularly and with an accurate gauge designed for low pressures in the range of 6 to 10 pound per square inch. A gauge designed for low-pressure ATV tires is recommended. Fluid from tires is extremely corrosive and may render gauges inaccurate very quickly, Hofman notes.

Ideally, tire pressures should be readjusted whenever changing a load on the tractor. Producers may want to adjust tire pressure for the heaviest load instead, says Hofman. That means tires may be somewhat overinflated for some uses but will never be underinflated.

Copyright North Dakota State University Ag Extension

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