What does a weight distribution hitch actually do?

A weight distribution hitch uses spring bars to lever some of the tow ball weight off the tow vehicle's rear axle and spread it back onto the front axle and the trailer's axles. It levels the combination, restores steering and headlight aim, and improves braking balance. It does not reduce the total weight you are towing and it does not change any of your rated limits.

Round bar or trunnion — which is better?

Round bar hitches hang the spring bars below the head and are the most common style in Australia, with the widest parts support and good tolerance of uneven ground. Trunnion bars slot horizontally into the head, sit higher and give more ground clearance, which suits vans with low A-frames. Performance is very similar when both are correctly sized and set up; availability and clearance usually decide it.

Does a weight distribution hitch increase towing capacity?

No. Your braked towing capacity, tow ball rating, GVM and GCM are set by the manufacturer and shown on the compliance plate. A WDH changes how the load is carried, not how much you are legally allowed to tow. Some manufacturers do require a WDH above a certain trailer mass, but that is a condition of using the existing rating, not an increase in it.

When do I need a weight distribution hitch in Australia?

Consider one when the tow ball weight causes visible rear sag, light steering, or headlights aiming skyward — typically from around 200 to 250 kg of tow ball mass on a mid-size ute or wagon. Many vehicle handbooks specify a WDH above a stated trailer mass. Always check your own handbook first, because some makers prohibit their use entirely.

Can you use a weight distribution hitch with an off-road coupling?

Usually not. Articulating off-road couplings such as the DO35, Treg and McHitch are generally not rated for the leverage a weight distribution hitch applies to the A-frame, and using one can void the coupling's approval. Check the coupling manufacturer's own guidance before fitting any WDH.

Guide

Weight Distribution Hitches in Australia: Types, Rules & Setup

What a WDH does and doesn't do, round bar versus trunnion, the vehicle and coupling rules that catch people out, and how to size and set one up properly.