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Technical Bulletins

Maximize Tractive Performance of Radial Rear Tractor Tires with Proper Inflation

Date: MAY, 1994

NOTE: This bulletin replaces F-039-X dated April 1992.

Many operators are not taking full advantage of their radial drive tires, especially when using duals and triples on large tractors. Studies have shown tires are being overinflated by as much as 20 psi.


How does tire pressure affect operating performance?


  • Loss of traction
  • Excessive soil compaction
  • Fast wear both in field and on road
  • Higher fuel consumption
  • Fewer acres tilled per day
  • Harsh ride
  • Impact breaks


  • Sidewall damage
  • Poor ride
  • Bead un-seating
  • Fast wear


  • Traction
  • Compaction
  • Wear
  • Fuel efficiency
  • Acres worked
  • Ride

Isn't the tire inflation OK as long as the tire does not have a big bulge?

This is a myth from the bias tire days when ANY kind of sidewall bulge meant the BIAS TIRE was low on air. RADIAL TIRES MUST HAVE A CERTAIN BULGE in order for the tire to develop its superior traction. (DIAGRAM INSERTED)BIAS TIRES, at their proper inflation, will OUTPULL an OVERINFLATED RADIAL.The radial's superior performance is realized only with proper inflation. See attached load/inflation tables.

Doesn't the tractor or tire dealer set the tires to the proper inflation when the tractor or new tires are delivered?

Unfortunately, they do not always set the inflation properly. New tractor tires are normally inflated to 30 psi when shipped from the factory to minimize bouncing on the trailer. Dealers may overlook reducing the tire pressures or may not reduce the pressure to the proper level for the load on the axle. Tire changers often times inflate tire to 35 psi to set the tire beads on the rim. Again, the pressure must be reduced to match the load on the axle. SAFETY WARNING: Never exceed 35 psi when mounting. For complete instructions, consult the 1991 Firestone Farm Tire Data Book (D402) available at all Firestone stores and dealers.

How does the operator set the tires to the proper inflation?

  • Determine the axle load for your tractor.
  • A grain elevator scale is best.
  • If an elevator scale is not available, call you tractor dealer for the tractor's front and rear axle load.
  • Include any cast or liquid weights, tanks, loaders and the implement hitch weight.* 
  • Divide the axle load by the number of tires on that axle.  
  • Turn to the single, dual or triple load table for your tire size. Begin at the left side of the table and move right until you either find the load for your tire or the next higher load. Move up the column to find the correct tire pressure.  
  • Set all the tires on the axle to that pressure.**  

Follow steps 1 through 4 for the second axle.

*When using heavy 3-point hitch mounted equipment, adjust rear inflation pressures based on the weight being carried on the rear axle with the implement raised. Return to the lower rear inflation pressures when using towed implements. NOTE: For towed implements which transfer heavy vertical loads to the drawbar (i.e., laser scrapers, grain carts), weigh tractor with maximum axle load and adjust inflation accordingly.

**It is very important to use an accurate tire gauge. Checking with a gauge that is off by 2 psi can lead to serious tire durability problems when setting tires at these lower pressures. Tires pressures fluctuate with air temperatures and should always be rechecked on a weekly basis.