“Managing the ballast and tire inflation pressures can maximize traction, minimize compaction, increase the life of the tractor drivetrain, and increase productivity,” says Dave Paulk, manager field technical services at BKT USA, Inc.
Proper ballast and inflation is also needed to get the most out of your equipment. “The bottom line is that if you’ve paid good money for horsepower, proper ballast is essential to make sure you’re getting your money’s worth,” says James Crouch, national product manager for agriculture at Yokohama Off Highway Tires.
Follow these six steps from Firestone Ag to adjust the ballast on your tractor.
1. IDENTIFY THE HORSEPOWER RATING OF YOUR TRACTOR
The correct horsepower rating depends on the type of tractor you’re using. For two-wheel drive (2WD) and mechanical front wheel drive (MFWD) tractors, use the rated PTO horsepower. For four-wheel drive (4WD) tractors, use the tractor’s rated engine horsepower.
This example will use a MFWD tractor with 180-PTO hp. that is being used to pull drawbar implements.
2. CALCULATE THE TARGET TOTAL TRACTOR WEIGHT
The target tractor weight is based on the driveline of the tractor. The chart below outlines the weight per horsepower.
| Tractor type | Target tractor weight |
| 2WD | 145 pounds/PTO hp. |
| MFWD | 130 pounds/PTO hp. |
| 4WD | 110 pounds/engine hp. |
To continue with the example, a MFWD tractor with 180-PTO hp. multiplied by 130 pounds would equal 23,400 pounds.
3. CALCULATE THE RECOMMENDED FRONT AND REAR AXLE WEIGHT SPLITS
Determining the weight split is also dependent on the tractor type and how it’s used. The chart below shows the target weight splits, according to standard industry practices.
| Tractor type | Front axle | Rear axle |
| 2WD | 25% | 75% |
| MFWD draw bar | 35% | 65% |
| MFWD 3-point hitch | 40% | 60% |
| 4WD | 51-55% | 45-49% |
“Keep in mind these are all target weight splits with no equipment mounted to the tractor,” says Bradley Harris, global agricultural field engineering from Firestone Ag. “If 3-point equipment is being used, make sure there is enough weight on the front axle to keep it on the ground.”
For the MFWD 180-PTO hp. tractor, there should be 8,190 pounds on the front axle (35% of 23,400 pounds) and 15,210 pounds on the rear axle (65% of 23,400 pounds).
4. WEIGH THE TRACTOR
The most accurate way to find the weight is to use a platform or portable scale, says Harris. “When weighing a tractor, make sure all of the fluids are topped off, especially the fuel tank,” he adds.
If you aren’t able to weigh your tractor, consult your operator manual or dealership. With most newer tractors the manufacturer has a procedure to calculate the tractor weight. However, if aftermarket items like saddle tanks or loaders are added, Harris recommends using a scale.
For the example MFWD 180-PTO hp. tractor, portable scales weighed in at 10,150 pounds on the front axle and 15,500 pounds on the rear.
5. ADD OR REMOVE WEIGHT
Using the target weight, adjust the weight distribution using cast weights or liquid. “Cast weights on MFWD and 4WD tractors are easier to work with if power hop becomes an issue,” says Paulk. “They are the most convenient and can be changed according to ballasting needs. Fluid is more economical, but is harder to change.”
In most cases, a tractor cannot be ballasted to the exact target weight.
In the example, the target front axle weight is 8,190 pounds but it weighed 10,150 pounds. Assume that the example tractor has six front suitcase weights. Since the front axle is heavier than the target weight, you would remove the suitcase weight and re-weigh the front axle, explains Harris. Even though the suitcase weights are 100 pounds, they add 130 pounds to the front axle because the weights are in front of the axle. When the weights are removed, the tractor is weighted and the new front axle weight is 9,370 pounds.
To follow the math: 6 suitcases multiplied by 130 pounds equals 780 pounds. The initial weight of 10,150 pounds minus 780 equals 9,370 pounds.
The correct weight will help keep slip within the recommended rates: 10-15% for 2WD tractors and 8-12% for 4WD and MFWD tractors.
“Too much weight can, in addition to using more fuel, mean not enough slip resulting in soil structure damage and possibly overstressing of transmission components,” says Mark Turner, senior product marketing manager for agriculture tires at Maxam Tire International. “Too little weight results in slip rates that are too high, which can mean longer time is required to finish the work and also lead to excessive fuel consumption.”
6. SET THE TIRE INFLATION PRESSURE
With the front and rear axle weights determined, you can use a tire inflation table to look up the minimum inflation pressure required to carry the load. Most tire manufacturers have free tire inflation pressure calculators on their websites or as an app, like this one from Firestone Ag. Plug in the type of equipment, tire setup, tire size, and input the axle load and the calculator will determine the minimum inflation pressure.
In this example, the front tires were 420/90R30 used as singles. The minimum inflation pressure to carry the 9,370 pounds is 17 psi. The rear tires were 480/80R46 used as duals. The minimum inflation pressure to carry the 15,500 pounds is 12 psi.
Soil compaction in the top 12 to 16 inches of soil is primarily a function of tire pressure, says Turner. “Below this level, compaction and structural soil damage is related to total vehicle weight,” he adds. “It is easy to see why correct ballasting that allows efficient traction and enables good speed across the ground is a major contribution to soil health.”
