Zero-turn mower

A zero-turn riding lawn mower (colloquially, a z-turn) is a standard riding lawn mower with a turning radius that is effectively zero. Different brands and models achieve this in different ways, but hydraulic speed control of each drive wheel is the most common method. Both commercial duty and homeowner models exist, with varying engine power options, size of cutting decks, fuel type (gasoline or diesel), and prices. A z-turn mower typically drives faster and costs more than a similarly sized conventional riding mower that has steerable front wheels.

Most current models have four wheels: two small swiveling front tires and two large drive tires in the back. Bush Hog mowers sometimes come with a small, pivoting fifth wheel mounted in the center behind the driver. Instead of controlling the swiveling tires to steer the machine, the large drive tires rotate independently of each other based on the driver's input. They may rotate in opposite directions. The mower can pivot around a point midway between the drive wheels (the classic z-turn), or it can pivot around either one of the drive wheels if one is stationary, or it can turn in a circle of any radius. Reversal of the direction of travel can be accomplished by causing both wheels to rotate in reverse.

Steering controls differ on z-turn mowers. Instead of a steering wheel, most z-turns have two throttles that control the rotational speed and direction of each drive wheel. The throttles are typically moved by a seated driver who operates levers mounted waist to shoulder high. The mower's engine throttle is controlled separately, if at all. Some zero turn mowers are steered by a joystick or a steering wheel, the advantage of either one being the location of the hands may permit less fatigue during prolonged mowing and the use of a single hand for steering.

In 1949, Warrensberg, MO resident Max Swisher invented the very first commercially available zero-turn mower and called it the "Ride King". It was a three-wheeled machine - one wheel in front and two in the rear. The patented system utilized the front wheel as the drive wheel that also was able to turn an amazing 360 degrees. The wheel was driven by the motor in the same direction 100% of the time. In order to reverse and/or utilize the zero turn capabilities, you simply turned the steering wheel 180 degrees and the mower would reverse course. In 1963, John Regier was an employee of the Hesston Corporation, a manufacturer of farm and agricultural equipment. The company had recently engineered a device called the swather, which, propelled by a series of belts, cut hay, alfalfa and other farming materials and laid them out in windrows. The way the belts and pulleys operated allowed for counter- rotation—a process which particularly struck Regier. An idea came to him one day: What if he could incorporate the same technology into lawnmowers?

...
Wikipedia