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Bulging Tires Build Profit

So what’s wrong with the tractor tire shown at right?  

Nothing, if the tractor that tire is on is only used to run around the farm without a load. But if that tire is in the field this spring doing tilling or planting work, its sidewall isn’t showing enough bulge (or deflection).

“You want to see a bulge, no matter how disconcerting it may seem. We were all raised to look at a tire with a bulge and think it automatically needs air,” says Tom Rodgers of Firestone. “The impact of overinflated tires is that they cost you more fuel, more time in the field, and more compaction.”

Proof of that is offered by field research. The USDA’s Agricultural Research Service finds that properly inflated tires generate nearly 25% more pull than tires running at higher pressures. 

Properly inflated tires also reduce the depth and degree of compaction in the top foot of the soil. Such compaction slays soybean yields, in particular, by limiting root growth, reducing nodulation, inhibiting potassium and phosphorus uptake, and promoting disease.

pinpoint weight

Determining the exact pressure of tractor tires depends on the tractor, how much weight it is carrying, and how it is being used, in addition to other factors. 

“The only way to know for sure what your tire inflation pressure should be is to take some time and do some calculations,” Rodgers urges. “Yes, it takes time. But really no more time than preparing  a planter or a piece of tillage equipment so that it operates accurately or efficiently during use.”

The process of determining exactly what a tractor’s tractive tire inflation starts with nailing down a tractor’s PTO hp., which is available online or from your dealer.

Next, take that horsepower times these weights:

  • For two-wheel-drive (2WD) tractors, a tractor should weigh 145 pounds for every 1 hp. it generates.
  • For front-wheel-drive (FWD) tractors, 130 pounds is needed for every 1 hp.
  • For four-wheel-drive (4WD) tractors, 110 pounds is needed for every 1 hp.

After you have determined how much weight your tractor should be carrying, you need to split that weight between the tractor’s front and rear axle according to this guide:

  • For 2WD tractors, 25% of total weight should be on the front axle and 75% on the rear axle.
  • For FWD tractors carrying hitch-mounted implements, the weight split should be 35% front axle and 65% rear axle.
  • For FWD tractors pulling an implement, the weight split should be 40% front axle and 60% rear axle.
  • For 4WD tractors, the weight split should be 55% front axle and 45% rear axle.

Rodgers provides an example using a typical row-crop vehicle, a John Deere 8530 FWD tractor.

“This is a 275 PTO hp. tractor,” he explains. “So you calculate 275 hp. multiplied by 130 pounds per hp. That adds up to 35,750 total pounds, which is what that tractor should weigh after adding ballast,” Rodger points out.

If this tractor is pulling a planter, you distribute added ballast on the tractors so that the front axle weighs 14,300 pounds and the rear axle weighs 21,450 pounds.

“See how much weight you have to add to the front and rear axles, separately,” says Scott Sloan of Titan Goodyear. “Do this by running the tractor on scales (at your local elevator) and weighing the front and rear axles separately.”

If you don’t have access to a scale, you can roughly calculate weight by looking at the front and rear axle weights supplied by the manufacturer (you can get that from your dealer).

Finally, divide the calculated weight by the number of tires per axle. This gives you the amount of weight each tire is carrying. Some adjustments will be needed before adding or adjusting ballast and then determining proper inflation pressure. For example, some weight is transferred from a drawn implement onto a tractor’s drawbar. That weight needs to be added to your calculations. “Three-point hitch-mounted implements can transfer more weight to a tractor,” Rodgers points out.

go to the tables

Use load and inflation tables (available from any tractor tire manufacturer website) and inflate tires to lowest recommended pressure per tire. “Always use the manufacturer’s recommendations for your tire configuration (single, dual, or triple tires) on each axle,” Rodgers says. “Adjust inflation whenever axle loads change.”

When it comes to taking inflation pressure, always “use a high-quality digital gauge,” Rodgers urges. “Inflation pressures can be so low these days (approaching as low as 6 psi) that an old-fashioned stick gauge can’t give you an exact reading. Buy a gauge that gives you reading down to 1∕10 psi for accuracy.”

Finally, don’t be alarmed if your tractor tires seem way underinflated. “There is a certain disbelief when the manufacturer’s data book says to inflate tires as low as 7 psi, for example,” Rodgers has found. “Trust those figures. Manufacturers construct their tires with more capacity than the tractor demands. That construction allows tires to run efficiently at lower pressure without damaging the tire.”

Lower pressures allow tires to deflect and, in doing so, create a longer tire footprint. That footprint distributes the weight load over more area to reduce ground pressure, thereby, reducing soil compaction. 

preplanting checklist for maximum traction

Before heading to the field this spring, add the following to-do items to your planting checklist.

  • Check all your tires’ sidewalls for cracks, cuts, or other damage.
  • Check tire tread. If there is less than 20% left on the tire, consider new tires, says Scott Sloan of Titan International.
  • Check the tread area for stubble damage and exposed cords. If any damage is detected, it’s time to replace the tires.
  • Check tire contact area to make sure there is no space between the lugs and the ground, says Brad Harris of Firestone Farm Tire.
  • Check tire valve stems, looking for cracks, corrosion, and dirt. Replace any missing valve caps.
  • Check nuts and bolts on rims to ensure they are properly tightened.
  • Write correct inflation pressures on all tires (tractor and implement) with a paint stick or use a stick you can get from most tire dealers. 
  • Check tire pressure at least weekly – if not daily. “Remember, inflation pressure can change several psi during the day as temperatures go up and down,” explains Firestone’s Tom Rodgers. 
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