The Synchro-Steer System
Zero-turn mowers use two rear transmissions to distribute energy, one powering each of the rear wheels. This is beneficial for creating zero-radius turns; with one rear wheel moving faster than the other, the moving wheel can initiate the turn and serve as the pivot point for the zero-radius circle. The transmissions of both rear wheels are operated independently, usually with a system called lap bars.
The big trouble with zero-turn mowers is found in the front wheels. Standard zero-turn mowers use casters in the front, wheels that pivot 360 degrees. The casters aren't attached to any part of the drive train; they move based on the motion initiated by the rear wheels. This allows for quick and easy movement around a zero-radius turn -- in theory.
As we've seen, lawns feature inclines and bumps and when the turf is wet, traction can become an issue. When the rear wheels begin a turn, they have to overcome resistance found in the front casters. This can lead to plowing in the front wheels, and when the front casters hold fast, the rear wheels can lose traction, leading to skidding and slipping. All of this adds up to turf damage.
The Synchro-Steer system was designed to overcome resistance found in the front wheels by never allowing it to generate in the first place. The solution is to initiate the turn at the front wheels, but control the speed at the rear wheels.
Like traditional zero-turn mowers, the Synchro-Steer system uses dual rear transmissions that distribute power to the rear wheels independently. When the steering wheel found aboard Synchro-Steer system mowers is turned, the steering box turns the front axle. But a pair of direct linkage connections that runs from the steering box to each of the rear transmissions adjusts the speed in the rear wheels as necessary.
For example, when a left (counterclockwise) turn is initiated, the linkage to the left rear transmission slows the speed of the left rear wheel. This moves the power to the right rear wheel, which carries out the zero-radius turn. Since the turn was initiated among the front wheels, there's no resistance to overcome, and hence no turf damage from plowing in the front or skidding in the rear.
It seems the Synchro-Steer engineers managed to combine Ackerman's steering with John Reiger's mower, while cutting Barney Oldfield out of the picture once and for all.
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