Attraction of traction
The big, smoky traction engines provided a link to the future
The big, smoky traction engines provided a link to the future through the Industrial Revolution.
You can call them tractor heads or prime movers, but the main power unit for hauling heavy loads has just one ancestor – and it had four legs. Slightly more recently though, the Industrial Revolution and its steamy glory meant that it was now possible to drive heavy loads over hill and dale.
In Great Britain, the term steam tractor is more usually applied to the smallest models of traction engine – typically those weighing seven tons or less – used for hauling small loads on public roads. Although known as light steam tractors, these engines are generally just smaller versions of the road locomotive.
They were popular in the timber trade in the UK, although variations were also designed for general light road haulage and showman’s use.
The most popular of these designs was probably the Garrett 4CD, which claimed to have four ‘compound horsepower’.
Designed for haulage of heavy loads on public highways, it was not uncommon for two or even three to be coupled together to allow heavier loads to be handled.
The characteristic features of these engines are very large rear driving wheels fitted with solid rubber tyres; three-speed gearing (most traction engine types have only two gears); rear suspension; and belly tanks to provide a greater range between the stops needed to replenish water.
All these features are to improve the ride and performance of the engine, which used to be used for journeys of hundreds of miles. Most road locomotives are fitted with a winch drum on the back axle. This can be used by removing the driving pins that secure the rear wheels, allowing the drive train to power the winch drum instead of the wheels.
A number of road locomotives are fitted with a crane boom on the front. The boom pivot is mounted on the front axle assembly, and a small winch is mounted on an extension to the smokebox in front of the chimney; the cable passing over a sheave at the top of the boom arm.
The winch is powered by bevel gears on a shaft driven directly from the engine, with some form of clutch providing control. These road locomotives can be used to load a trailer as well as to haul it to a new location. They are often referred to as ‘crane engines’.
A particularly distinctive form of road locomotive was the Showman’s engine. These were operated by travelling showmen both to tow fairground equipment and to power it when set up; either directly or by running a generator.
These could be highly decorated and formed part of the spectacle of the fair. Some were fitted with a small crane that could be used when assembling the ride.