Hydrostatic walk-behind lawn mowers use a hydraulic pump to provide the power to the wheels. A belt-driven mower uses belts to supply the power. Some hydro-driven models have a separate pump for each wheel, resulting in quick, agile steering. Overall, hydrostatic walk-behind mowers are easier to use and more versatile, but they are also more expensive to buy and repair.
The gas motor in a hydrostatic mower uses a pulley to run the hydraulic pump that powers the wheels. If one wheel turns faster than the other, the mower will move on a curved path. If the wheels turn in opposite directions or if one wheel stops while the other keeps turning, the mower will pivot in a 180-degree circle. This is called a zero turn, a capability of hydrostatic mowers. Likewise, the operator can shift the direction of the wheels to reverse, a capability that belt-driven machines do not have. A belt-driven machine uses a belt to drive the wheels, making the mower less flexible and requiring more effort by the operator.
Mowers driven by belts are by far the cheapest. Hydro-driven mowers are much more expensive. Lawnandlandscape.com says a hydro-driven mower can cost from $700 to $1,000 more than a comparable belt-driven model. The added expense is a cost of doing business for lawn care professionals but might be a budget-buster for a homeowner with a small lawn. Golf courses and turf maintenance professionals get more productivity out of hydro-driven walk-behind mowers.
A mower driven by a belt has no reverse. If you can only go forward, the inability of a belt-driven mower to back up may be an issue. Belt-driven mowers usually have pistol-grip steering systems, making them awkward and hard to use. Hydro-driven mowers are considered easier to negotiate around tight curves in a lawn, flower beds, trees and other obstacles. Many hydrostatic models have variable speeds so the operator can slow down or speed up with ease.
The belts on belt-driven mowers sometimes slip, especially in wet weather. Belt-driven mowers require more maintenance, usually in the form of tightening and replacing belts, but the repairs are easier and cheaper than those on hydro-driven mowers. The hydraulic oil and filters usually have to be replaced once a year on the hydrostatic models.
Belt-driven mowers require more work to operate; they are best used for backup mowers or for a small yard. Hydro-driven mowers are better for larger lawns. A hydro system delivers more torque to the wheels, making the push-behind mower easier to use on hilly lawns. A hydro-driven push mower is likely better for an older operator or for persons lacking physical strength or endurance.