Where you place the load determines how the weight is distributed across the front and rear axles. Here is how to use the moment principle to check whether you are staying below the axle limits.
Introduction
Even if you stay below the permitted gross weight, you can easily exceed an axle load if the load is placed incorrectly. The position of the load shifts weight between the front and rear axle according to the moment principle — it is pure statics.
The moment equilibrium
The kerb weight acts at the vehicle's own centre of gravity, and the load at its own. If you place a heavy load right at the rear, the rear axle can become overloaded while the front axle is relieved — which impairs both steering and braking.
How to measure in practice
- 01Weighbridge: drive the whole vehicle onto the scale for the gross weight.
- 02Axle weight: weigh each axle or axle group separately where possible.
- 03The moment method: if you know the position of the dead weight and the load, the axle loads can be calculated — that is what the calculator does.
Worked example — 2-axle lorry
En 2-akslet lastbil har akselafstand L = 5,0 m. Egenvægten er 7.000 kg med tyngdepunkt 2,0 m foran bagakslen. Vi lægger en palle på 3.000 kg 1,0 m foran bagakslen. Hvad bliver akseltrykkene?
- 01Foraksel: R_f = Σ(vægt · afstand til bagaksel) / L = (7.000 · 2,0 + 3.000 · 1,0) / 5,0 = 17.000 / 5,0 = 3.400 kg.
- 02Bagaksel: R_b = total − R_f = (7.000 + 3.000) − 3.400 = 6.600 kg.
- 03Flyt nu pallen til 0,5 m bag bagakslen (afstand −0,5 m): R_f = (14.000 − 1.500) / 5,0 = 2.500 kg, R_b = 10.000 − 2.500 = 7.500 kg.
By moving the 3,000 kg from 1.0 m in front to 0.5 m behind the rear axle, 900 kg shifts from front to rear axle. If the rear axle's limit is, for example, 10,000 kg (single axle), there is still room — but a heavier load placed incorrectly can quickly exceed the limit, even though the total weight (10,000 kg) is far below the allowed weight.
Table: before and after moving centre of gravity
| Load placement | Front axle | Rear axle |
|---|---|---|
| 1.0 m in front of rear axle | 3.400 kg | 6.600 kg |
| Over the rear axle | 2.800 kg | 7.200 kg |
| 0.5 m behind rear axle | 2.500 kg | 7.500 kg |
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