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

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 FT4/Stage IV 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 Unballasted Tractor Weight Charts on following pages, front axle weight is 3963 kg (8736 lb.) and rear axle weight is 5720 kg (12611 lb.). These charts assume that a front weight support is mounted and does not include effect of a front hitch.
NET changes from deducting front support and adding front hitch are to add 277 kg (611 lb.) to front axle and subtract 93 kg (205 lb.) from rear axle.
900 kg (1984 lb.) block weight when attached to a Front Hitch adds 900 x 1.44 = 1296 kg (2857 lb.) to front axle and subtracts 900 x 0.44 = 396 kg (873 lb.) from rear axle due to leveraging.
Combine all of these as shown:
	Front Axle	Rear Axle
Base Tractor	3963 kg (8736 lb.)	5720 kg (12611 lb.)
Front Hitch	+277 kg (611 lb.)	-93 kg (205 lb.)
900 kg (1984 lb.) Block on Front Hitch	+1296 kg (2857 lb.)	-396 kg (873 lb.)	Total
Totals	5536 kg (12203 lb.)	5231 kg (11512 lb.)	10767 kg (23715 lb.)

Tractor is ballasted to level of 10767 kg (23715 lb.) / 230 Eng-HP = 47 kg (103 lb.) per Eng-HP (Medium)

Percentage of weight on front axle is 5720 kg / 10767 kg (12611 lb. / 23715 lb.) x 100% = 53.1%.

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

Front Inflation Pressure = 1.5 bar (22 psi)

Rear Inflation Pressure = 0.6 bar (9 psi) 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 aid of an assistant, visually check tire deflection when tractor is pulling hard in field to confirm tires are not under-inflated with these pressures.

For trailers, tankers, or any heavy integral implement rear inflation pressures must be increased substantially to support extra weight at transport speeds. Exact amount depends on extra load. Usually it will be more than double 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

7210R FT4/Stage IV MFWD with CommandQuad™, Standard Front Weight Support, No Front Hitch, and No Front Suspension — 210 Eng-HP
	Front Tires	420/85R34
	Rear Tires	480/80R50
	Front Ballast	10 Suitcase Weights on Front Support
	Rear Ballast	1 pair - 625 kg (1378 lb.) Wheel Weights
From Unballasted Tractor Weight Charts, front axle weight is 3963 kg (8736 lb.) and rear weight is 5720 kg (12611 lb.).
Ten suitcase weights [43 kg (95 lb.) each] on standard front support add 10 x 43 x 1.44 = 619 kg (1365 lb.) to front axle and subtract 10 x 43 x 0.44 = 189 kg (417 lb) from rear axle due to leveraging.
Pair of rear 625 kg (1378 lb.) wheel weights adds nothing to front axle and 1250 kg (2756 lb.) to rear axle.
Combine all of these as shown:
	Front Axle	Rear Axle
Base Tractor	3963 kg (8736 lb.)	5720 kg (12611 lb.)
10 Front Suitcase Weights	+619 kg (1365 lb.)	-189 kg (417 lb.)
1 Pair 625 kg (1378 lb.) Wheel Weights	0	+1250 kg (2756 lb.)	Total
Totals	4582 kg (10102 lb.)	6781 kg (14950 lb.)	11363 kg (25052 lb.)

Tractor is ballasted to level of 11363 kg (25052 lb.) / 210 = 54.1 kg (119 lb.) per Eng-HP (Light).

Percentage of weight on front axle is 4582 kg / 11363 kg (10102 lb. / 25052 lb.) x 100% = 40.3%

From Recommended Pressures tables for calculated axle loads, required inflation pressures are:

Front Inflation Pressure = 0.8 bar (12 psi)

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

This is ideal configuration for a 7210R MFWD tractor without front suspension when it is used with towed tillage implements such as disks, chisels, and field cultivators. Front weight percentage should be approximately 40% or less to help prevent power hop. Although this tractor is slightly under 40%, it is close enough. Power hop can still occur, but it can be controlled using procedures given in this section. If percentage is much higher, control may not be possible.

When this tractor is used to tow large trailers, 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.