Tractor axle load with implements and ballast

Hitching an implement moves weight between the tractor's axles. A lifted rear implement adds more than its own weight to the rear axle and lifts the front axle at the same time. A front weight does the opposite. Axle loads decide whether the tractor steers and brakes safely, whether the tyres can carry the load, and what pressure they need.

Terms

Unladen weight – the tractor without implements or ballast.
Weight distribution – the share on the front axle, for example 40 %.
Wheelbase (L) – the distance between the axles in metres.
Distances (a, b) – from the axle to the implement's centre of gravity.

The formulas

The calculation is a moment balance: the turning moment from the implement's weight about one axle must be taken by the other.

Rear-mounted implement of weight W with its centre of gravity b metres behind the rear axle:

Front axle: − W × b ÷ L Rear axle: + W × (L + b) ÷ L

Front implement or front weight of weight W, a metres ahead of the front axle:

Front axle: + W × (L + a) ÷ L Rear axle: − W × a ÷ L

Drawbar or hitch load: treat it like a rear implement, using the distance from the rear axle to the hitch point.

The changes always add up to the weight you added, which makes a useful check.

Worked example step by step

In our tractor data the Case IH Puma 215 weighs 8,400 kg with a wheelbase of 2.88 m. The 40 % front weight split and the implements below are invented examples.

1. Tractor alone

Front 8,400 × 0.40 = 3,360 kg, rear 8,400 × 0.60 = 5,040 kg.

2. Lifted rear implement: 1,800 kg, 1.5 m behind the rear axle (example)

Front: 1,800 × 1.5 ÷ 2.88 = 937.5 kg less → 2,423 kg
Rear: 1,800 × 4.38 ÷ 2.88 = 2,737.5 kg more → 7,778 kg
Check: 2,423 + 7,778 ≈ 10,200 = 8,400 + 1,800 ✔

The front axle now carries only about 24 % of the total. Many operator's manuals state a minimum front axle share for steering and braking, often around 20 %. Check what applies to your tractor.

3. Add a front weight: 900 kg, 1.0 m ahead of the front axle (example)

Front: 900 × 3.88 ÷ 2.88 = 1,212.5 kg more → 3,635 kg
Rear: 900 × 1.0 ÷ 2.88 = 312.5 kg less → 7,465 kg
Check: 3,635 + 7,465 = 11,100 = 8,400 + 1,800 + 900 ✔

The front share is now about 33 %. The front weight also unloads the rear axle because it levers over the front axle.

From axle load to tyre pressure

With two tyres per axle, step 3 gives about 1,818 kg per front tyre and 3,733 kg per rear tyre. With Michelin Multibib 540/65R30 front and 650/65R42 rear, Michelin's tables give:

	Load/tyre	Field 10 km/h	Road 40 km/h
Front 540/65R30	1,818 kg	0.4 bar (carries 1,950)	0.8 bar (carries 1,975)
Rear 650/65R42	3,733 kg	0.8 bar (carries 3,885)	1.2 bar (carries 4,000)

The lowest pressure in the table is not always the practical one. Very low pressures under high torque can let the tyre slip on the rim, and some manufacturers set conditions for high-torque use. See tractor tyre pressure.

Ballast – enough, not too much

Too little: high slip, uneven wear and poor steering, especially with heavy rear implements.
Too much: more compaction, higher rolling resistance and fuel use, and unnecessary load on tyres and axles.
Reasonable slip in heavy draft work is commonly quoted as about 10–15 % in the field. Much higher slip suggests too little weight or the wrong pressure.
Liquid-filled tyres add ballast low down but are hard to remove when not needed. Wheel weights and front weights are more flexible.

Common mistakes

Counting the implement's weight but forgetting its distance.
Forgetting the drawbar load of a heavy trailer.
Not adjusting tyre pressure when changing implements.
Exceeding permitted axle loads or tyre capacity in transport. Dynamic loads from bumps and braking come on top of the static load.

Example: drawbar load from a loaded trailer

The same Puma 215, without plough or front weight, hitched to a trailer giving 2,000 kg on the hitch, 0.6 m behind the rear axle. The drawbar load and distance are invented examples.

Front: 3,360 − 2,000 × 0.6 ÷ 2.88 ≈ 3,360 − 417 = 2,943 kg
Rear: 5,040 + 2,000 × 3.48 ÷ 2.88 ≈ 5,040 + 2,417 = 7,457 kg

The rear axle gets almost as much as with the plough, so rear pressure must go up for transport. With Michelin Multibib 650/65R42 and about 3,730 kg per tyre, Michelin's table needs 1.2 bar at 40 km/h, because 1.0 bar only carries 3,555 kg.

How much front ballast is needed?

Calculate the front axle load with the rear implement, as above.
Decide the front axle load you want to reach, for example the manual's minimum.
Work out the difference ΔF.
Front weight needed: W = ΔF × L ÷ (L + a), where a is the distance ahead of the front axle.

Example: with the plough the front axle had 2,423 kg. To reach 3,000 kg needs 577 kg more. With a = 1.0 m and L = 2.88 m, W = 577 × 2.88 ÷ 3.88 ≈ 428 kg. The 3,000 kg target is only an example.

Checklist before transport

Raise and lock the implement in transport position.
Check the front axle share and total axle loads against the manual.
Raise tyre pressure to the road value for load and speed.
Check the tyres' speed symbol against your speed.
Check lights, warning boards and implement width.

Troubleshooting: signs of too little front load

Steering feels light or vague, especially with a heavy linkage implement.
Front wheels slip or bounce under draft.
The tractor rears when starting off or on slopes.
Braking feels weaker, because the front wheels brake less.

These can be serious safety issues. Check the load distribution and add front ballast as the manual says.

Seasonal tips

Spring: drills and heavy harrows change weight distribution. Recalculate when changing implement.
Harvest: loaded trailers give high drawbar loads. Check the rear axle and pressure.
Autumn: the plough is often the heaviest rear implement. Check the front share.
Winter: a front snow blade and a rear sand spreader are new load cases; calculate them the same way.

How Lastkalkyl calculates

Lastkalkyl (load calculator) uses the same static moment balance about the rear axle, with lifted implements and no dynamic additions. You enter:

Unladen weight, front share (%) and wheelbase. For many models weight and tyres are pre-filled. If the wheelbase is missing, an estimate from weight is used and labelled as estimated.
Front and rear implements with weight and distance.
Optionally the drawbar load and its distance.
Front and rear tyres from the catalogue.

The app shows axle loads and load per tyre, checks them against the tyres' load capacity by load index at the tyre's speed symbol (ISO 4251), and suggests the lowest pressure from the manufacturer's table for field (about 10 km/h) and road (about 40 km/h).

Open Lastkalkyl (load calculator) in the app

Frequently asked questions

How does a rear implement affect the front axle?

The front axle is unloaded by W × b ÷ L, where W is the implement weight, b its distance behind the rear axle and L the wheelbase. The rear axle gains W × (L + b) ÷ L.

Why does a front weight reduce the rear axle load?

It sits ahead of the front axle and acts as a lever: the front axle gains more than the weight itself, and the rear axle is unloaded by W × a ÷ L.

How much weight should be on the front axle?

The tractor manufacturer specifies it. Many manuals give a minimum for steering and braking, often around 20 % of total weight.

How do I calculate how much front weight I need?

Front weight W = ΔF × L ÷ (L + a), where ΔF is the wanted increase in front axle load, L the wheelbase and a the distance ahead of the front axle.

Does a loaded trailer increase rear axle load?

Yes. Drawbar load acts like a rear implement: the rear axle gains more than the drawbar load while the front axle is unloaded.

Last updated 2026-10-15. General information. See disclaimer.