A ballast tractor is a heavy haulage road vehicle designed to pull or push heavy or exceptional loads. Unlike the tractor unit from an articulated trailer, the ballast tractor is designed or adapted to pull or push loads from a drawbar. By contrast an articulated tractor unit pulls from a fifth wheel, and only pushes when reversing its load.
Ballast tractors may have all wheel drive, or any useful combination of driven axles.
Derivation of the name
The name ballast
is derived from the nautical term (see sailing ballast
) describing heavy material added to a vessel to improve stability. In the case of a ballast tractor, weight must be added over the driving wheels to increase the available tractive effort
. The weight increases the friction between the tyres and the road surface. Without such ballast, the tractor would be unable to overcome the inertia of a heavy trailed load, and its wheels would rotate without generating forward motion.
Apart from being used by fairgrounds as a direct replacement for the steam powered showman's engine, specialist moving and haulage companies use ballast tractors. These include:
When deployed as a showman's engine, many users mount a separately powered generating set
on the rear of the ballast tractor, which is used to power fairground attractions, while the pure ballast tractor used in general haulage is not so equipped.