How heavy can an unbraked trailer be on Northern Ireland roads?

As a general rule, an unbraked trailer used behind a car in Northern Ireland must not exceed 750 kg MAM, and the towing vehicle may impose a lower unbraked limit.

For Northern Ireland motorists, the key is to use the NI rule rather than assuming a Great Britain article says exactly the same thing. The 750 kg figure is not permission to tow that weight behind every car. Vehicle manufacturers specify separate braked and unbraked towing capacities.

For this exact issue — “How heavy can an unbraked trailer be on Northern Ireland roads?” — separate four things that are often confused: the entitlement on the NI driving licence, the trailer’s plated MAM, the towing vehicle’s manufacturer limits and the actual laden weight of the combination. Insurance and roadworthiness sit on top of those limits; meeting one figure does not make an otherwise overweight, unbraked or uninsured setup lawful.

Use the lower applicable figure from the trailer and vehicle specifications. If the trailer has brakes, they must be serviceable and compatible with the towing system. Where the facts of a journey or vehicle differ from the ordinary case, check the exact DfI/DVA or nidirect rule before travelling rather than extrapolating from a similar situation.

Before publishing this answer, the key factual point in “How heavy can an unbraked trailer be on Northern Ireland roads?” was checked against current Northern Ireland official guidance. That matters because road rules, licence entitlements and enforcement details can differ from Great Britain and can change over time; the sources attached below are the ones to re-check if the rule is updated.