The only contact between tractor and soil is the tire. It is also the only opportunity farmers have to connect their fuel investment to their land investment.
The obvious exceptions are rubber track tractors that do an excellent job putting down the power while removing most of the variables that exist with tires.
However, if producers have round rubber tires under their tractors, they have variables with which to gain optimum tractor performance and reduce diesel consumption.
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When ballast and tire inflation are correct, the engine transfers the optimal amount of power to the ground and thus burns the least amount of fuel for the work performed.
When tires are not tuned, tractor performance is lower and petroleum energy wasted.
Over and underballasting will waste fuel and prevent farmers from extracting the most work from their tractors.
Overballasting is the most common mistake, according to the Prairie Agricultural Machinery Institute (PAMI) and the Alberta Farm Machinery Research Centre.
An overballasted tractor will feel like it doesn’t have enough power and will burn more fuel because of excess weight.
The tractor may also experience premature drive train failures, according to PAMI.
Tire condition provides the first visual clue that a tractor is overballasted. If tires aren’t wearing as quickly as expected it’s possible there has not been enough slippage.
If the tractor reaches 4,000 hours and the drive tires still have nice square lugs, that indicates it has been firmly anchored to the soil by excess ballast. The tires would show wear if there had been the correct amount of ballast and slippage.
Another clue is galling on the teeth of the final drive planet pinion, which occurs when a tractor burns a lot of extra fuel that produces no work.
Underballasting is just as bad. The first clue is quick tread wear, caused by excessive slippage. Not only do producers pay for early tire replacement, but they pay in wasted diesel fuel every time the tire turns without performing the optimal amount of work.
Ballast controls wheel spin. Front-wheel assist and four-wheel drive tractors are designed for eight to 12 percent slippage.
A conventional two-wheel drive tractor is designed to have 10 to 15 percent slippage.
Ground speed is a slippage factor many people overlook. Higher ground speed requires less ballast because the mechanical properties of the soil allow only a limited degree of deformation in a given period of time.
If a tractor tire is slowly rolling over the soil, it gives the soil more time to give and deform and allow the tire to slip. A slower tractor needs more ballast.
On the other hand, a tire that quickly rolls over the soil gives it less time to deform and allows less slippage. A faster tractor needs less ballast.
There are general recommendations for total tractor weight at different speeds. For example, at a working field speed of six mph, a tractor should weigh 108 pounds per one engine horsepower. This means a 200 h.p. tractor at six mph should have a total ballasted weight of 21,600 pounds for optimal performance.
If ground speed drops to four mph, the total tractor weight jumps to 163 lb. per h.p. The same tractor now needs a total ballasted weight of 32,600 lb.
These figures are provided by PAMI and the Alberta Farm Machinery Research Centre to serve as a starting point for producers to make their own calculations. Manufacturer recommendations will vary, so it’s best to check the manual or a dealer for the exact data.
The significant answers begin to be apparent once producers get into the field to measure wheel slip at full power and the speed at which the tractor will be worked.
This procedure documents the number of wheel turns over a fixed distance with the tractor unloaded, but at the producer’s normal ground speed.
That number is compared to the number of wheel turns over the same fixed distance with the tractor under full load at normal ground speed.
The operator’s manual outlines the procedure. Newer tractors have radar sensors to indicate actual slip in real time.
As producers try to extract the most work from each gallon of diesel burned, they realize total tractor weight is only one part of the equation. Weight distribution front-to-back is another.
Front-wheel assist tractors should carry 40 percent of total weight at the front and 60 percent at the rear.
Four-wheel drive tractors need 55 percent of total weight at the front and 45 percent at the rear.
On conventional two-wheel drive tractors, 70 percent of the weight goes over the rear tires and the remaining 30 percent goes to the front. That may seem like an odd balance, but on many two-wheel drive tractors, weight will need to be added to the front to reach that percentage.
The debate of chloride ballast versus iron ballast continues, with chloride still the price favourite despite problems with wheel corrosion and environmental concerns. If global metal prices continue their long-term climb, chloride may continue as the price favourite.
Cast iron weights don’t cause corrosion and have the extra advantage of being removable if ballast needs to be changed for different tasks. Once chloride is in the tire, it usually stays there.
If producers want liquid ballast in their tires but don’t want to risk corroding their steel rims and valve stems, they can consider an environmentally friendly liquid ballast called Rim Guard Tire Ballast.
This liquid ballast is made of de-sugared molasses, which is a byproduct from sugar beet plants. It remains fluid at – 40 C and costs about 28 cents per pound.
Regular chloride weighs 11 and 11.5 lb. per gallon. The molasses product is slightly lighter at 10.7 to 11 lb. per gallon.
If there’s a spill, plants and animals benefit from the nutrients because it is organic, but the main advantage is that it will not corrode the wheels.
Once the correct ballast has been determined, other factors must be considered.
Pressures higher than 35 psi can be dangerous. The pressure recommendations molded into the sidewall are maximum pressures for maximum load. Using these higher pressures when the load isn’t maximum can adversely affect tire and tractor performance.
Some producers hike up the tire pressure to stiffen the sidewall so it supports more weight.
However, a tire that is stiffer and harder causes more slippage and soil compaction. It wastes diesel fuel, digs deeper ruts and lets the tractor get stuck in soft spots.
Check tire pressures regularly, even those difficult inner duals.
When running duals or triples, follow the manufacturers’ recommendation for all tires on the same axle.
Use an accurate pressure gauge, especially when checking low-pressure tires. An error of two psi isn’t too important on a tire that’s inflated to 30 psi. However, an error of two psi on a pressure of 12 psi is a 20 percent mistake that will have a major impact on tire and tractor performance.
Producers should remember that if they change tire sizes, they need to start from scratch to figure out the right ballast, weight distribution and tire pressure.
Tire manufacturers are working to develop new technology to increase tire efficiency. One example is the new Uniflex Axiobib radials that Michelin introduced recently when it dropped all non-radial tires from its ag lineup. Michelin calls the basic concept Ultraflex because the sidewall is extremely flexible.
Michelin says the new tires can operate at inflation pressures 20 percent lower than its regular MachXBib radial. Conversely, when run at the same pressure as standard radials, the new tire can carry 20 percent more load.
The tires create a 22 percent larger footprint so the tire transfers more power to the ground. More power to the ground means better traction and better fuel economy.
For more information on molasses ballast, visit www.rimguard.biz.
For more information on Ultraflex, visit www.michelinag.com.
