Linda Benedict | 12/2/2005 1:11:14 AM
It seems obvious that a wider or faster mower will cover a lawn faster than a narrower or slower mower, but this is not always true. And seldom will the increase in cutting rate be proportional to the increase in width or speed, according to an engineer with the LSU AgCenter.
"The effects of width and speed are interrelated, and both are affected by a term engineers call ‘efficiency,’ or ‘field efficiency’ in the case of farm implements," says Dr. Richard Parish.
"With any mowing operation – or any other tractor operation, for that matter – not all of your time is spent actually mowing," Parish says. "You’ll spend some time turning at the sides or ends of the lawn. You may also slow down occasionally to maneuver around trees, bushes or other obstacles.
"You may have to stop occasionally for chores like emptying a grass catcher or unplugging a machine or to move the kids’ toys and the dog’s bones out of the way," he adds. "All of these things reduce your efficiency compared with just driving in a straight line at optimum speed."
With a big, rectangular lawn, no obstacles and no grass catcher, Parish says mowing efficiency might exceed 90 percent.
"In other words, you might be actually mowing at optimum speed over 90 percent of the time," he says.
On the other hand, if your lawn is typical, you will have a much lower efficiency, and your efficiency will decrease with increasing mowing width and speed.
Parish says that while it seems logical that if you trade your mower in on a new one that’s 50 percent wider, you’ll be able to mow 50 percent more lawn per hour. Unfortunately, it isn’t so in most cases.
"As you move to a wider mower, your non-productive time will become a greater portion of your total time, and thus your efficiency will decrease," he says.
Parish says farm machinery such as planters and harvesters typically need to increase width by a factor of three or four in order to double productivity per hour.
"Mowers are not quite this bad (unless you use a grass catcher that has to be emptied), but nevertheless the relationship is not linear," the engineer says. "As you increase width, efficiency decreases, and in some cases you can actually reduce mowing rate.
"If the additional time spent maneuvering a wider mower exceeds the time saved by the wider cut, you will lose capacity."
Parish says the effect of speed is similar to the effect of width. Increasing speed does not result in a proportional increase in mowing rate because you still have to turn at the ends of the lawn and still have to maneuver around trees and obstacles.
"This nonproductive time becomes a greater percentage of total time as your speed increases, and thus your efficiency will drop with speed," he says. "In some cases, increasing width will require reducing speed, thus negating the effect of a wider mower."
Parish says often moving to a wider or faster mower means using a different type of machine.
"Therefore, it’s important to look at the overall picture," he says. "Some mower configurations are more efficient than others. It’s possible that one mower configuration will have a wider deck while another configuration offers higher speed or higher efficiency.
Parish offers two real-life examples to illustrate the situation. In one case, a 72-inch finishing mower on the back of a compact tractor was replaced with a 52-inch zero-turning radius mower. The smaller, zero-turn mower was able to cut the four-acre area in slightly less time than the 72-inch mower because the area contained many trees, a pond and multiple plantings – all of which required lots of maneuvering, and the zero-turn mower was much more maneuverable.
In the second case, the same 72-inch finishing mower on a compact tractor replaced a garden tractor with a 42-inch mid-mounted deck. In this case, mowing time decreased from six hours to two hours because the seven-acre lawn was mostly open with few obstacles, so the greater width and speed of the compact tractor/finishing mower combination could be used effectively.
"These examples illustrate the importance of considering the lawn situation and the type of mower/tractor rather than looking only at width or speed," Parish says.
"You have to consider your mowing conditions and type of mower as well as width and speed," Parish says. "The same principles apply to other implements such as tillage implements or garden spreaders."