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

Example 1

The Unballasted Tractor Weight Charts provides front axle, rear axle and total weights for all power train and tire size options. Considering this and the 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 Recommended Pressure Charts in Wheels, Tires, and Treads section.

 
8230 PST with Independent Link Suspension and Front Weight Support - 200 PTO-HP
       
  Front Tires 420/90 R30  
  Dual Rear Tires 480/80 R46  
  Front Ballast Weight Support
  Rear Ballast None  
       
According to the Unballasted Tractor Weight Charts on following pages, the front axle weight is 4534 kg (9995 lb) and the rear axle weight is 6674 kg (14713 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 Weight 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 4534 kg (9995 lb) 6674 kg (14713 lb) 11208 kg (24708 lb)
Front Weight Support 250 kg (551 lb) -80 kg (176 lb) 170 kg (375 lb)
Total 4784 kg (10546 lb) 6594 kg (14537 lb) 11378 kg (25083 lb)

 

So the tractor is ballasted to the level of 11378 kg (25083 lb) / 200 PTO-HP = 56.9 kg (125 lb) per PTO-HP (Medium).

The percentage of weight on the front axle is 4784 kg / 11378 kg (10546 lb / 25083 lb) x 100% = 42%.

From the Table of Recommended Inflation Pressures in Wheels, Tires, Treads (section 80) for calculated axle loads, the required inflation pressures are:

Front Inflation Pressure 140 kPa (1.4 bar; 21 psi)

Rear Inflation Pressure 60 kPa (0.6 bar; 9 psi) but only if tractor is towing an implement that places very little 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 420/90 R30  
  Rear Tires 480/80 R46  
  Front Ballast 4 QUIK-TATCH Weights on Front Support
  Rear Ballast 1 pair - 635 kg (1400 lb) Wheel Weights and
1 pair - 75 kg (165 lb) Wheel Weights
       
According to the Unballasted Tractor Weight Charts, the front axle weight is 3899 kg (8595 lb) and the rear is 6674 kg (14713 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)
       
Front Axle Weight ADDED by 4 QUIK-TATCH Weights: 47 kg (104 lb) x 4 x 1.55 = 292 kg (644 lb)
Rear Axle Weight REMOVED by 4 QUIK-TATCH Weights: 47 kg (104 lb) x 4 x -0.55 = -104 kg (228 lb)
       
The pair of rear 635 kg (1400 lb) wheel weights and 75 kg (165 lb) wheel weights add nothing to the front axle and 1420 kg (3130 lb) to the rear axle.
       
Combine all of these as shown
  Front Axle Rear Axle Total
Base Tractor Weight 3899 kg (8595 lb) 6674 kg (14713 lb) 10573 kg (23310 lb)
Weight Support 247 kg (544 lb) - 77 kg (169 lb) 170 kg (375 lb)
4 QUIK-TATCH Weights 292 kg (644 lb) - 104 kg (228 lb) 188 kg (416 lb)
1 Pair 635 kg (1400 lb) Wheel Weights 0 kg (lb) 1270 kg (2800 lb) 1270 kg (2800 lb)
1 Pair 75 kg (165 lb) Wheel Weights 0 kg (lb) 150 kg (330 lb) 150 kg (330 lb)
Total 4438 kg (9783 lb) 7913 kg (17446 lb) 12351 kg (27231 lb)

 

So the tractor is ballasted to the level of 12351 kg (27231 lb) / 225 = 55 kg (121 lb) per PTO-HP (Medium).

The percentage of weight on the front axle is 4438 kg (9783 lb) / 12351 kg (27231 lb) x 100% = 36%

From the Table of Recommended Inflation Pressures in Wheels, Tires, and Treads for the calculated axle loads, the required inflation pressures are:

Front Inflation Pressure 120 kPa (1.2 bar; 18 psi)

Rear Inflation Pressure 80 kPa (0.8 bar; 12 psi) but only if the tractor is towing an implement that places very small load on the drawbar (planter or air seeder).

This is the ideal configuration for a 8330 MFWD tractor 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. Although this tractor is slightly over 35%, it is close enough. Power hop can still occur, but it can be controlled using the procedures given in this section of the manual. If the percentage is much higher, control may not be possible.

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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