CAT 143H Motor Grader Tire Inflation

[MikePhua]

Common Issue: Blade Walking During Finishing
Operators of the CAT 143H motor grader often experience a problem where the blade "walks" or drifts sideways during finishing work. This behavior can negatively affect the quality of grading by causing uneven surfaces. One common factor influencing this issue is tire inflation pressure, especially when using radial tires like Continental radials.
Recommended Tire Pressure Ranges
For the CAT 143H with 17.5R25 tires, typical recommended tire pressures vary but often fall in the range of:

• Front tires: 45 to 55 psi
  
• Rear tires: 40 to 50 psi
  

Exact pressures may depend on tire ply rating and load. For example, 10-ply tires might have lower max pressures compared to 12-ply tires, which can handle higher psi.
Effect of Tire Pressure on Traction and Blade Control

• Higher tire pressures tend to reduce tire footprint, decreasing traction. This can cause less control of the blade and contribute to blade walking.
  
• Lower tire pressures increase the footprint and traction but might accelerate tire wear or risk tire damage if too low.
  
• Balancing the pressure to optimize traction while protecting tires is key to stable blade operation.
  

Strategies Used by Operators to Mitigate Blade Walking

• Some operators use differential tire pressures where diagonal pairs have different pressures, for example:
  • Front-left and rear-right tires at a slightly higher psi (4-5 psi more) than their opposite tires.
    
  • This pattern helps stabilize lateral movement and reduce the walking effect though it may not eliminate it completely.
    
• Adjusting pressures slightly from recommended specs during finishing passes based on surface condition can improve control.
  

Additional Considerations

• Tire condition and tread type (radial vs bias-ply) influence traction and blade behavior. Radials provide better flotation but may slip more at high psi.
  
• Surface conditions such as moisture, grade, and material type affect needed pressures and blade control.
  
• Regularly check tire pressures with a quality gauge to maintain consistency.
  

Terminology Explained

• Blade Walking: Unintended lateral movement of the grader blade causing uneven grading.
  
• Tire Footprint: The contact area of the tire with the ground, impacting traction.
  
• Radial Tire: Tire with cords arranged radially, offering improved traction and wear properties over bias-ply tires.
  
• Diagonal Tire Pressure Pattern: A scheme where tires on diagonal axles have staggered pressures to improve vehicle stability.
  

Operator Experience and Anecdote
An experienced superintendent from Alberta shared that running tires at about 50-55 psi usually balanced traction and tire life well on a CAT 143H. However, when blade walking occurred, applying a slight pressure difference diagonally helped improve stability. Others reported running slightly lower pressure on rear tires for better traction while keeping fronts higher for steering precision.
Conclusion
Proper inflation of tires on a CAT 143H motor grader is a critical factor in controlling blade walking during finishing work. Tire pressures typically recommended range between 40 and 55 psi depending on ply rating and tire type. Differential inflation patterns across diagonals can mitigate side-to-side blade movement. Operators are encouraged to adjust pressures based on field conditions while monitoring tire health to optimize grader performance and finish quality.