Determining Ballasted Tractor Weight, Weight Split, Axle Loads and Required Tire Inflation Pressures

Example 1

The Unballasted Tractor Weight Charts provide front axle, rear axle and total weights for all power train and tire size options. From this and information previously provided on weights of various ballast elements (QUIK-TATCH weights and wheel weights), front ballast multipliers and front hitch axle loads (if used),

the ballasted tractor weight and axle loads can be calculated. These are needed to determine if total weight and weight split recommendations are met and to look up required tire inflation pressures from the Recommended Pressures charts in Wheels, Tires, and Treads section.

 
8230 PST with Independent Link Suspension and Front Weight Support- 200 PTO-HP
       
  Front Tires 480/70 R30  
  Rear Tires 710/70 R38  
  Front Ballast Weight Support
  Rear Ballast None  
       
According to the Unballasted Tractor Weight Charts on following pages, the front axle weight is 4767 kg (10510 lb) and the rear axle weight is 6280 kg (13844 lb). Note that these charts do not assume that a front weight support is mounted.
       
Front Axle Weight ADDED by Front Weight Support: 170 kg (375 lb) x 1.47 = 250 kg (551 lb)
Rear Axle Weight REMOVED by Front Support: 170 kg (375 lb) x -0.47 = -80 kg (176 lb)
       
Combine all of these as shown
  Front Axle Rear Axle Total
Base Tractor Weight 4767 kg (10510 lb) 6280 kg (13844 lb) 11047 kg (24354 lb)
Front Weight Support 250 kg (551 lb) -80 kg (176 lb) 170 kg (375 lb)
Total 5017 kg (11061 lb) 6200 kg (13668 lb) 11217 kg (24729 lb)

 

So the tractor is ballasted to the level of 11217 kg (24729 lb) / 200 PTO-HP = 56.1 kg (124 lb) per PTO-HP (Light)

The percentage of weight on the front axle is 5017 kg (11061 lb) / 11217 kg (24729 lb) x 100% = 45%.

From the Recommended Pressures charts in Wheels, Tires, Treads section for calculated axle loads, the required inflation pressures are:

Front Inflation Pressure: 165 kPa (1.65 bar; 24 psi)

Rear Inflation Pressure 75 kPa (0.75 bar; 11 psi) but only if tractor is towing an implement that places very little down load on drawbar (planter or air seeder).

For implements that generate high weight transfer add approximately 50 kPa (0.5 bar; 7 psi) for a total of

110 kPa (1.1 bar; 16 psi) for rear tires. With the aid of an assistant, visually check tire deflection when tractor is pulling hard in the field to confirm that tires are not under-inflated with these pressures.

For trailers, tankers, or any heavy integral implement , the rear inflation pressures MUST be increased substantially to support the extra weight at transport speeds. The exact amount depends on the extra load. Usually it will be MORE THAN DOUBLE the base amount or 130 - 150 kPa (1.3 - 1.5 bar; 19 - 22 psi) for this example. To determine rear axle load exactly, weigh rear axle of loaded tractor on a platform scale.

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Example 2

 
8330 PST with MFWD and Standard Front Weight Support - 225 PTO-HP
       
  Front Tires 540/65 R34  
  Rear Tires 520/85 R46  
  Front Ballast Weight Support
  Rear Ballast 1 pair - 635 kg (1400 lb) Wheel Weights and
2 pair - 205 kg (450 lb) Wheel Weights
       
According to the Unballasted Tractor Weight Charts, the front axle weight is 4224 kg (9312 lb) and the rear is 6175 kg (13612 lb). Note that these charts do not assume that a front weight support is mounted. The weight for the weight support and transfer effect is found in the section on attaching front weights.
       
Front Axle Weight ADDED by Front Weight Support: 170 kg (375 lb) x 1.45 = 247 kg (544 lb)
Rear Axle Weight REMOVED by Front Weight Support: 170 kg (375 lb) x -0.45 = -77 kg (169 lb)
       
The pair of 635 kg (1400 lb) rear wheel weights and two pairs of 205 kg (450 lb) wheel weights add nothing to the front axle and 2090 kg (4608 lb) to the rear axle.
       
Combine all of these as shown
  Front Axle Rear Axle Total
Base Tractor Weight 4224 kg (9312 lb) 6175 kg (13612 lb) 10399 kg (22924 lb)
Weight Support 247 kg (544 lb) -77 kg (169 lb) 170 kg (375 lb)
1 Pair 635 kg (1400 lb) Wheel Weights 0 kg (lb) 1270 kg (2800 lb) 1270 kg (2800 lb)
2 Pair 205 kg (450 lb) Wheel Weights 0 kg (lb) 820 kg (1808 lb) 820 kg (1808 lb)
Total 4471 kg (9857 lb) 8188 kg (18051 lb) 12659 kg (27908 lb)

 

So the tractor is ballasted to the level of 12659 kg (27908 lb) / 225 PTO-HP = 56 kg (124 lb) per PTO-HP (Light).

The percentage of weight on the front axle is 4471 kg (9857 lb) / 12659 kg (27908 lb) x 100% = 35%

From the Recommended Pressures charts in Wheels, Tires, and Treads section for the calculated axle loads, the required inflation pressures are:

Front Inflation Pressure: 110 kPa (1.1 bar; 16 psi)

Rear Inflation Pressure: 160 kPa (1.6 bar; 23 psi) but only if the tractor is towing an implement that places very little load on the drawbar (planter or air seeder).

This is the ideal configuration for a 8330 tractor equipped with MFWD when it is used with towed implements such as planters or air seeders. The front weight percentage should be approximately 35% or less to help prevent Power Hop. Power Hop can still occur, but it can be controlled using the procedures given in this section.

When this tractor is used to tow large trailers, the rear inflation pressure must be increased as outlined in Example 1.

If this tractor is used with heavy integral or semi-integral implements, additional front ballast and higher rear inflation pressures will be required.

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