The weight is distributed across the front and rear axle according to the position of the centre of gravity. Here's how to calculate the distribution — and stay under the axle-load limits.
Introduction
Even if the total overall weight is within limits, a single axle can be overloaded if the load is skewed. Luggage compartment, passenger placement and fuel shift the centre of gravity and thus the distribution on the axles.
The formula (2 axles)
Example: a bus of 18,000 kg with a wheelbase of 6.0 m and the centre of gravity 3.6 m behind the front axle. F_rear = 18,000 · 3.6/6.0 = 10,800 kg, F_front = 7,200 kg. If the rear axle is then below its limit (e.g. 11,500 kg for a drive axle), there is margin — but if the centre of gravity is moved further rearward, the limit may be exceeded.
- 01Single axle: max. 10,000 kg (the Danish dimensions regulation).
- 02Drive axle with twin tyres + road-friendly suspension: max. 11,500 kg.
- 03Distribute heavy luggage and cargo so that no axle goes over its limit.
Three-axle bus — the common one
Most large city buses and long tour buses have three axles: a steering front axle, a drive axle (typically with dual tyres) and a trailing or lifting axle at the rear (or in front of the drive axle). The two-axle formula does not work here, because the weight is now distributed over three points. In practice, you calculate the front axle separately and treat the two rear axles as an axle group, whose mutual distribution depends on the suspension.
Regneeksempel: en 3-akslet bus på 24.000 kg med afstand foraksel → bagakselgruppens midte L = 5,4 m og tyngdepunkt x_tp = 4,3 m bag forakslen (bagtung pga. hækmotor og fuld bagperron). F_bag_gruppe = 24.000 · 4,3/5,4 = 19.111 kg, og F_for = 24.000 − 19.111 = 4.889 kg. Forakslen bærer altså kun 4.889/24.000 = 20,4 % af vægten.
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