There are three trailer measurements that will help to find the correct towing solution:
- Aggregate Trailer Mass (ATM) The total mass of the laden trailer when carrying the maximum load recommended by the manufacturer. This includes the towball weight and is measured when the trailer is not coupled to the tow vehicle. The ATM will be specified by the trailer manufacturer and must not be exceeded. You can find this by looking at the id plate on the trailer or by contacting the manufacturer.
- Gross Trailer Mass (GTM) The mass transmitted to the ground by the axle or axles of the trailer when coupled to the towing vehicle and carrying its’ maximum load approximately uniformly distributed over the load bearing area. The GTM will be specified by the trailer manufacturer and must not be exceeded. You can find this by looking at the id plate on the trailer or by contacting the manufacturer.
- Ball Weight The weight imposed on the tow vehicle’s towball from the coupling of a trailer. Ball weight is often around 10% of the ATM. The ball weight can be determined by using a weighbridge.
This can be done by disconnecting the fully laden trailer from the tow vehicle and resting only the trailer’s draw bar (via the jockey wheel) on the scales.
A vehicle’s towing capacity is determined by the vehicle manufacturer. The manufacturer will specify:
- The maximum towing mass for the vehicle
- The maximum ball weight for the vehicle