Ag Section Circle

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The Right Tire Pressure

 

The Issue

The quality of your harvest and preservation of your land.

Over Inflated tires cause excessive soil compaction with the formation of ruts (in damp conditions).
The consequences:

  • The root development of the crops planted is adversely affected
  • Limited development of microbial life
  • Stagnation of water is encouraged

The results:

  • Loss of yield.
  • Lower quality results.
  • Excess operating costs resulting from extensive work such as deep tillage to break the compaction layer.
The Performance Tractors and Combines

Over inflation increases the amount of spin and depth a machine sinks into the soil.
The consequences:

  • Excessive spin
  • High resistance to forward movement due to the "step" effect, caused by ruts

The results:

  • Excess fuel consumption
  • Time wasted
  • Wear on machine and tires

The right pressure means an optimum soil contact and therefore a larger footprint which causes spin and penetration to be reduced.

The service live of your tires

The wrong pressure may have a serious effect on the life of your agricultural tires:

  • Over inflation causes excessive spin in the fields. On hard, stony soil, it causes premature wear. On the road, over inflation causes fast, irregular wear on the lugs – the footprint is too small.
  • Under inflation causes irreversible damage to tire casings: risk of failure. It also leads to excessive wear on roads: too much rolling resistance.
Your comfort

The wrong pressure affects your comfort:

  • Over inflation causes bouncing and vibration.
  • Under inflation causes power handling. Maneuvering at low speeds or on the spot is more difficult.

4 Criterias to Calculate the Right Pressure

1- The sizes of tires and their characteristics (load and speed index)
2- The maximum speed at which you use your machines
3- The total weight supported by your tires = machine weight + weight of tools + load transfer
4- Operating use: cyclical or non-cyclical

Take an example:

  • Tractor + Front weight and 3 point implement, max. speed 25mph/40 kph.
  • Front tires: Michelin Machxbibs 600/65R28 154A8 / 154B
  • Rear tires: Michelin Machxbibs 650/75R38 169A8 / 169B.

Weight per tire on the front axle:
Total weight front axle: 9920 lbs (Weight of front axle) + 660 lbs (Weight Transfer) + 1984 lbs (Weight Transfer) – 2204 lbs (Shedding of the rear load transfer) = 10,361 lbs 4,700 Kg
Total weight per front tire: 10,361 lbs / 2

Weight per tire on the rear axle:
Total weight rear axle: 11464 lbs (weight of rear axle) + 2204 lbs (Weight transfer on Implement) + 4400 lbs (Weight of Implement) – 660 lbs (Shedding of front load transfer) = 17416 lbs
Total weight per rear tire: 17416 lbs / 2 = 8,708 lbs

Dimensions Max. Speed Load per Tire Pressure
600/65R28 154A8 / 154B

25 mph

5180 lbs

14.5 psi

650/75R38 169A8 / 169B 8708 lbs

Notes: Pressure calculation
Be careful, the pressure of agricultural tires must always be calculated using maximum load and speed without damaging your tires.

The weight of a vehicle may change according to use, when the front weight is removed, for example. In this case, the rear tires will have to support an additional weight equivalent to the front load transfer. This additional weight means that the pressure of the rear tires must be increased, or they will be damaged.

To avoid adjusting pressures, it is advisable to retain the load transfers in the calculation of the axle weight. In the above example, you should therefore add onto the front axle the 661 lbs of the front tool load transfer and add the 2204 lbs of the rear tool load transfer onto the rear axle.

For traction work (E.g.: plowing/deep tillage) if the tractor is not used on the road, the pressure per tire should be defined according to the field speed.

Notes: Balance of pressure
Should the work being carried out not call for a high level of traction and the levels of pressure between front and rear tires differ considerably (E.g.: 14 psi at the front and 22 psi at the rear), it is advisable to balance the pressure of the 4 tires to the highest pressure to satisfy the mechanical balance ratios for tractors.

The Risks of Incorrect Pressure

Pressure Too High Pressure Too Low
Excessive soil compaction
Extensive rut formation
Excessive spin (overconsumption)
Fast, irregular wear on roads
High risk of tearing tread blocks
Uncomfortable ride
Risk for tire casing durability
Rotation on wheel rim
Irregular wear on roads
Overconsumption on roads
Vehicle instability