Tire Size, Location, and Pressure
Tire size and location play a crucial role in determining the recommended air pressure for tractor tires.
Tire Size
Larger tires require lower inflation pressures to carry the same load compared to smaller tires.
Tire manufacturers provide load/inflation tables specific to each tire size to determine the proper pressure based on the axle load.
For example, an 800/70R38 tire may require only 12 psi to carry 9,261 lbs at 5 mph, while a smaller 480/80R46 tire would need higher pressure for the same load.
Tire Location (Front vs Rear)
Rear tractor tires should be inflated to much lower pressures (typically 12-18 psi) than the maximum sidewall rating to maximize traction, minimize compaction, and reduce wear.
Front tractor tires can be inflated closer to the maximum sidewall pressure, usually around 25-35 psi.
The rear tires carry most of the weight and require lower pressures to increase the footprint area and traction.
Axle Load
The axle load (weight on each axle) is the primary factor in determining the recommended tire pressure for that axle's tires.
Heavier axle loads require higher inflation pressures to prevent overloading and sidewall damage.
Weighing the loaded axles (e.g. at a grain elevator scale) provides the axle loads to look up the proper pressure in the load tables.
In summary, larger tires and rear tractor tires utilize much lower pressures than smaller tires and front tires respectively. But the axle load is the key variable that must be matched to the tire size and location using the manufacturer's load/inflation data to determine the optimal pressure.
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