Steam wagon

A steam wagon (or steam lorry, steam waggon or steamtruck) is a steam-powered truck for carrying freight. It was the earliest form of lorry (truck) and came in two basic forms: overtype and undertype, the distinction being the position of the engine relative to the boiler. Manufacturers tended to concentrate on one form or the other.

Steam wagons were a widespread form of powered road traction for commercial haulage in the early part of the twentieth century, although they were a largely British phenomenon, with few manufacturers outside Great Britain. Competition from internal-combustion-powered vehicles and adverse legislation meant that few remained in commercial use beyond the Second World War.

Although the majority of steam wagons have been scrapped, a significant number have been preserved in working order and may be seen in operation at steam fairs, particularly in the UK.

Design features

The steam wagon came in two basic forms:

The overtype design drew much from traction engine practice, and used an engine unit that consisted of a locomotive type boiler, with the cylinders, crank shaft, and motion mounted on top of the boiler. The rear axle was typically driven by a chain from the engine unit. The engine unit was attached to a chassis with the load carrying body attached.

The undertype designs used a conventional chassis, and had a self-contained engine mounted separately from the boiler, typically (although not exclusively) under the chassis. To allow for firing and water management, the boiler remained in the cab.