Description
Four-wheel-drive tractors use articulate steering, which is a system by which a vehicle is split into front and rear halves connected by a vertical hinge. These tractors are designed to pull very large loads on wide open spaces. Tires are the same size on both the front and rear axles. Horsepower ranges from 250 to 500 or more. Transmissions are standard or shift-on-the-go with up to 20 forward gears and several reverse gears. They are equipped with climate-controlled cabs and have many of the same features described for front-wheel-assist tractors. These include power seats, finger-tip controls, and features to give optimum engine efficiency and hydraulic performance. Multiple hydraulic control valves for remote devices are available. Tractors are equipped with a drawbar hitch; a three-point hitch is optional. Dual or triple wheels are commonly used on both front and rear. An option available from some manufacturers is a rubber-track instead of rubber tires.
Application
Four-wheel-drive tractors are powerful and are used to pull very wide implements or implements pulled in tandem. Wheels can be adjusted for row crops. They are commonly used to pull very large subsoilers, disks, chisel plows, air seeders, and land leveling scrapers. Wheels can be adjusted for row crops. Required traction is obtained by following the manufacture’s recommendations for tire size, wheel weights, liquid added to the tires, and weight distribution (front to rear ratios). If not in balance, a noticeable vibration called “power hop” occurs under stressful pulling conditions. Reduced traction occurs during power hop and the resulting vibration can damage the tractor. Tractors used on debris-littered rangeland require special tire modifications (see section on Tractor Modifications for Rangeland Use). The rubber-track system overcomes much of the soil compaction problem associated with rubber tires, and when properly weighted, track systems are more stable on slopes.
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References / Additional Information
See also the description and explanation of Tractors and Torque.