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

The Unballasted Tractor Weight Charts provide front axle, rear axle, and total weights for most power train and tire size options. From them and information previously provided on weights of various ballast elements (suitcase weights and wheel weights), front ballast multipliers and front hitch axle loads (if used), the ballasted tractor weight and axle loads can be calculated. They are needed to determine if total weight and weight split recommendations are met and to look up required tire inflation pressures.

Example 1

7230R MFWD with CommandQuad™, Front Suspension, and Front Hitch — 230 Engine HP
	Front Tires	420/85R34
	Rear Tires	480/80R50
	Front Ballast	900 kg (1984 lb) Block on Front Hitch
	Rear Ballast	None
From the Unballasted Tractor Weight Charts on following pages, the front axle weight is 4542 kg (10013 lb) and the rear axle weight is 6338 kg (10898 lb). These charts assume that a front weight support is mounted and do not include effect of a front hitch.
The NET changes from deducting the front support and adding the front hitch are to add 500 kg (1102 lb) to the front axle and subtract 135 kg (298 lb) from the rear axle.
The 900 kg (1984 lb) block weight when attached to a Front Hitch adds 900 x 1.44 = 1296 kg (2857 lb) to the front axle and subtracts 900 x 0.44 = 396 kg (873 lb) from the rear axle due to leveraging.
Combine all of these as shown:
	Front Axle	Rear Axle
Base Tractor	4542 kg (10013 lb)	6338 kg (13973 lb)
Front Hitch	+500 kg (1102 lb)	-135 kg (298 lb)
900 kg (1984 lb) Block on Front Hitch	+1296 kg (2857 lb)	-396 kg (873 lb)	Total
Totals	6338 kg (13973 lb)	5807 kg (12802 lb)	12145 kg (26775 lb)

So the tractor is ballasted to the level of 12145 kg (26775 lb) / 230 Eng-HP = 53 kg (117 lb) per Eng-HP (Medium +)

The percentage of weight on the front axle is 6338 kg / 12145 kg (13973 lb / 26775 lb) x 100% = 52.2%.

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

Front Inflation Pressure = 1.5 bar (22 psi)

Rear Inflation Pressure = 0.6 bar (9 psi) but only if tractor is towing an implement that places very little down load on drawbar (disk or field cultivator).

For semi-integral plows or towed implements that generate high weight transfer add approximately 0.5 bar (7 psi) for a total of 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 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.

Example 2

7215R MFWD with AutoQuad™ PLUS, Standard Front Weight Support, No Front Hitch, and No Front Suspension — 215 Eng-HP
	Front Tires	420/85R34
	Rear Tires	480/80R50
	Front Ballast	10 Suitcase Weights on Front Support
	Rear Ballast	1 pair - 635 kg (1400 lb) Wheel Weights
From the Unballasted Tractor Weight Charts, the front axle weight is 2920 kg (6438 lb) and the rear is 4513 kg (9956 lb).
The 4 suitcase weights (50 kg [110 lb] each) on the standard front support adds 10 x 50 x 1.44 = 720 kg (1587 lb) to the front axle and subtracts 10 x 50 x 0.44 = 220 kg (485 lb) from the rear axle due to leveraging.
The pair of rear 635 kg (1400 lb) wheel weights adds nothing to the front axle and 1270 kg (2800 lb) to the rear axle.
Combine all of these as shown
	Front Axle	Rear Axle
Base Tractor	2920 kg (6438 lb)	4513 kg (9956 lb)
4 Front Suitcase Weights	+720 kg (1587 lb)	-220 kg (485 lb)
1 Pair 635 kg (1400 lb) Wheel Weights	0	+1270 kg (2800 lb)	Total
Totals	3640 kg (8025 lb)	5263 kg (11603 lb)	8903 kg (19628 lb)

So the tractor is ballasted to the level of 8903 kg (19628 lb) / 215 = 41.4 kg (91.3 lb) per Eng-HP (Light).

The percentage of weight on the front axle is 3640 kg / 8903 kg (8025 lb /19628 lb) x 100% = 41%

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

Front Inflation Pressure = 0.8 bar (12 psi)

Rear Inflation Pressure = 0.9 bar (13 psi) Only if the tractor is towing an implement that places little load on the drawbar.

This is the ideal configuration for a 7215R MFWD tractor without front suspension when it is used with towed tillage implements such as disks, chisels, and field cultivators. 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. 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.