The Complete Handbook of Motor Vehicle Trailers

Chapter 1: Understanding Motor Vehicle Trailers

A motor vehicle trailer is not a vehicle. That is the first fact to internalize. A vehicle, by regulation and by design, contains its own power source and its own braking system capable of bringing it to a controlled stop under all normal operating conditions. A trailer has neither. It is a load-carrying structure with two or more wheels, attached to a powered vehicle by a mechanical coupling, and it places demands on that towing vehicle — demands on its powertrain, its brakes, its suspension, and its frame — that the vehicle was never designed to handle alone. The instant you attach a trailer, you have created a new machine: a combination unit. The behavior of that combination unit is governed by physics, and the physics are unforgiving.

The most useful way to understand a trailer is as a system with four interacting subsystems: the structural frame and deck, the suspension and running gear, the coupling and tongue, and the electrical and braking provisions. Everything else — the sides, the roof, the tailgate, the dump hoist, the refrigerator, the spare tire mount — is cargo on top of that basic architecture. When you evaluate a trailer, you are evaluating those four subsystems. A 7,000-pound gross vehicle weight rating (GVWR) utility trailer with a badly designed tongue will drag its rear axle through a dip in a driveway and scrape its frame on a speed bump. A 25,000-pound equipment trailer with undersized brakes will overheat