Loading Trailer Weight Distribution…
Name, weight, then how far back from the coupling that item’s own centre sits: Generator, 85, 1.1. Use one unit of weight and one of distance throughout and the answers come back in the same ones — the distances only ever appear as a ratio.
Centre of the ball to centre of the axle. Twin axles: the midpoint between them.
Measured on a gauge or scales, not calculated.
Leave blank unless your own documents give you a figure. This page will not.
46.8 (10.4%)
450 on the trailer altogether, of which 403.2 is carried by the axle.
This page computes where weight ends up. It does not say what your vehicle may tow, what your towbar or coupling is rated for, what nose weight is permitted, or whether any arrangement is safe to drive. Those limits are printed on the vehicle plate, the towbar plate, the coupling and the trailer plate, and the lowest of them governs regardless of what the others allow. No figure here should be read as approval.
The lever is the whole of it. An item a quarter of the way from the coupling to the axle puts three quarters of its weight on the ball; an item sitting directly over the axle puts none there at all; an item behind the axle subtracts. That is why moving one heavy thing a short distance changes the nose weight far more than adding several light ones, and why the nose weight is measured on a gauge afterwards rather than trusted from a calculation.
Weight over the axle is not free either: what leaves the coupling arrives at the tyres, bearings and suspension, and the empty trailer’s own nose weight is taken here as a measurement rather than derived, because where a trailer’s chassis, floor and body balance is a property of that trailer. Weigh it, do not assume it.
Everything on a trailer is held up by exactly two things: the axle underneath it and the tow ball at the front. Any weight placed between them is shared out in inverse proportion to how far it sits from each, which is the same arithmetic as two people carrying a ladder. Put an item a quarter of the way back from the coupling and three quarters of its weight goes onto the ball. Put it directly over the axle and the ball takes none of it at all.
Written down, the share landing on the coupling is the item’s weight multiplied by the distance from the item to the axle, divided by the distance from the coupling to the axle. Because the distances appear only as a ratio, the units cancel: metres and feet give identical answers provided one of them is used throughout, and every weight comes out in the unit it went in as.
Consider an empty trailer weighing 180 with 20 already resting on the coupling, its axle three units of distance behind the ball. A 40 toolbox at 1.8 contributes 16. An 85 generator at 2.5 contributes 14.2. A 120 stack of timber sitting directly over the axle at 3.0 contributes nothing whatsoever.
A 25 spare wheel hung at 3.4, behind the axle, contributes minus 3.3: it does not merely fail to help, it actively lifts the front of the trailer. Add those to the 20 the empty trailer already applied and the coupling carries 46.8 of a 450 total, which is 10.4%, leaving 403.2 on the axle.
Move the timber a short way forward and that single change swamps everything the smaller items are doing. This is the practical lesson hiding in the arithmetic: one heavy object shifted slightly matters far more than several light ones rearranged.
An item loaded behind the axle removes its own potential contribution and then subtracts on top of that, so the term goes negative. It also sits far from the trailer’s centre of rotation, which increases how strongly the trailer resists changing direction and how hard it swings once it starts.
A trailer whose weight has drifted rearward, and whose nose has consequently gone light, is the arrangement behind most of the alarming stories. Describing that mechanism is not the same as setting a limit for it, and this page describes rather than prescribes.
The arithmetic knows where weight ends up. It does not know what your towing vehicle is plated for, what the towbar is rated at, what the coupling itself is rated at, or what the trailer’s own plate permits. Those four figures are independent, they are printed on four different plates, and the lowest of them governs regardless of how generous the other three are.
So no output here is an approval. Use the calculation to understand which way to move a load and roughly how much difference that will make, then confirm the result on a nose weight gauge or a set of scales, because the position of any real object’s centre of gravity is an estimate until it is weighed.
This page will not name one, because the figure depends on your vehicle, your towbar, your coupling and your trailer, and any of the four can be the binding limit. Look it up in those four documents, then type the percentage you were given into the target field and the arithmetic will solve for it.
Not to the arithmetic. Distances enter only as a ratio, so they cancel, and every weight comes back in whatever unit you typed. The one rule is consistency: do not mix metres with feet on the distances, or kilograms with pounds on the weights, or the ratio quietly stops meaning anything.
Measure to the midpoint between the two axle centres, which treats the pair as one support in the middle. That is an approximation, because tandem axles rarely share load perfectly evenly and the sharing shifts as the trailer pitches, but it is close enough to tell you which direction to move a load.
Because where a bare trailer balances is a property of that trailer — its chassis, floor, sides, ramp, jockey wheel and spare carrier all sit in different places on different models. Nothing about a length and an axle position predicts it, so it is asked for here as a measurement rather than guessed at.