Tire Expert Center
Aug 21, 2018
How can I get the most efficiency from my tractor?
To get the most efficiency from a tractor it’s critical to have the proper amount of ballast and the weight appropriately split between the front and rear axle. There are some general rules that tractor and tire manufacturers use when helping customers set up tractors used for fieldwork. These guidelines help make sure there is enough weight on the tractor to transmit the horsepower to the ground, while making sure the tractor is not so heavy that horsepower is wasted trying to move the tractor. To properly set up a tractor, a short five-step procedure can be used:
Step One: Identify the horsepower rating of the tractor. For 2WD and mechanical front wheel drive (MFWD) tractors, the rated PTO horsepower is used. For 4WD tractors, the tractor’s rated engine horsepower is used. For the following calculations, we will use a MFWD tractor with 180 PTO horsepower being used to pull drawbar implements as the example.
Step Two: Calculate the target total tractor weight. The target tractor weight is based on the driveline of the tractor. Chart 1 has the target weight per horsepower for the three types of tractor
Chart 1: Weight per horsepower recommendations
Example Target Tractor weight: 180 PTO HP x 130 LBS/PTO HP = 23,400 lbs.
Step Three: Calculate the recommended front and rear axle weight splits. Just like determining the tractor weight, the weight split is based on the tractor type and how the tractor is being used. Chart 2 has the target weight splits, according to standard industry practices. Keep in mind these are all target weight splits with no equipment mounted to the tractor. If 3-point equipment is being used, make sure there is enough weight on the front axle to keep the front axle on the ground.
Chart 2: Weight Split Targets
Example Tractor Weight Splits:
Front Axle 35%: 23,400 lbs. x 0.35 = 8,190 lbs.
Rear Axle 65%: 23,400 lbs. x 0.65 = 15,210 lbs.
Step Four: Weigh the tractor. The most accurate way to find the weight is to use a scale. This can be done on a platform scale or on portable scales. When weighing a tractor, make sure all the fluids are topped off, especially the fuel tank. If for some reason the tractor cannot be weighed, please consult your operator manual or your equipment dealership. With most newer tractors, the manufacturer has a procedure to calculate the tractor weight based on the base tractor and the weight package on the tractor. If aftermarket items (Saddle tanks, loaders, etc.) are added to the tractor, I recommend using a scale.
Example Tractor weighed with portable scales:
Front axle: 10,150 lbs.
Rear axle: 15,500 lbs.
Step Five: Add or remove weight. In most cases a tractor cannot be ballasted to the exact target weight outlined in Chart 2. In the example, the target front axle weight is 8,190 lbs., but it weighed 10,150 lbs. Let’s assume the example tractor has six front suitcase weights. Since the front axle weight is heavier than the target weight, we would remove the suitcase weight and re-weigh the front axle. Even though the suitcase weights are 100 lbs., they add 130 lbs. to the front axle because the weights are in front of the axle. When the weights are removed, the tractor is weighed and the new front axle weight is 9,370 lbs.
Step Six: Set the inflation pressure of the front and rear tires. Now that the front axle and rear axle weights are known, we can use the tire inflation tables to look up the minimum inflation pressure required to carry the load. To help customers with setting correct pressures, most tire manufactures have free tire inflation pressure calculators on their websites or as an app. On FirestoneAg.com, there is a new inflation pressure calculator to help determine the recommended inflation pressure. With these calculators, all the customer needs to do is select the type of equipment being used, select the tire setup (singles, duals, triples), enter the tire size, and input the axle load. The calculator will determine the minimum inflation pressure required to carry the load. In this example, the front tires were 420/90R30 used as singles. The minimum inflation pressure to carry the 9,370 lbs. is 17 psi. The rear tires were 480/80R46 used as duals. The minimum inflation pressure to carry the 15,500 lbs. is 12 psi.
When the tires are inflated to the recommended inflation pressure, the tire is able to develop the proper footprint. Proper inflation pressures allow the tire to develop the maximum traction, minimize tire wear and allow the tire’s sidewall to flex without causing damage to the tire. If the inflation pressure drops below the minimum recommended inflation pressure, the tire will over deflect, or squat more, which will cause internal damage or faster wear. However, over-inflating tires (even by 10 to 15 psi) will reduce the footprint size, reducing traction and increasing soil compaction. To get the most performance out of a tire, it is so important to check tire pressures daily when using the tractor.
If a tractor’s setup doesn’t change, and the tire configurations stay the same all the time, the axle weights and recommended inflation pressures will not change on the tractor. But if the duals are removed on the rear axle, the inflation pressure on the inside tires needs to increase to 23 psi to carry the 15,500 lbs. If the tractor is going to pull a 3-point ripper, it is necessary to weigh the tractor with that 3-pt ripper attached to the tractor to get accurate axle weights. Those new axle weights should be entered into a tire inflation calculator to find the new minimum inflation pressure.
Tractor setup and setting the tire inflation pressure is not a hard job, but it does take time to properly determine the weight needed on the tractor. Weighing the tractor, using tools like a tire inflation calculator to determine the recommended inflation pressure, and using an inflation pressure gauge to check the pressure are easy ways to remove the guesswork and increase efficiencies in the field.