Ballast tractor
A ballast tractor is a specially weighted tractor unit of a heavy hauler combination. It is designed to utilize a drawbar to pull or push heavy or exceptionally large trailored loads. When feasible, lowboy-style semi-trailers are used to minimize a load's center of gravity. Typical drivetrains are 6×4 and 6×6.
Typical ballast tractor loads include oil rig modules, bridge sections, buildings, ship sections, and industrial machinery such as generators and turbines.
Only a handful of manufacturers produce dedicated ballast tractors. Extra heavy duty chassis versions of mass-production tractor units are fitted with drawbar hitches and a separate ballast box as an alternative.
Increasingly, remote-controlled self-propelled modular transporters (SPMT) are being employed in traditional ballast tractor/trailer roles.
Description
The ballast tractor's name derives from the nautical term "sailing ballast" describing heavy material added to a vessel to improve stability. For a ballast tractor, ballast is added over the driving wheels to maximize traction. The additional weight increases the friction between the tyres and the road surface, allowing the tractor to overcome the inertia and friction of moving a heavy trailed load. Without it, there would be unproductive wheelspin.
