PAYBACK FROM NARROW TIRES
Here are the estimated production losses from spraying late in the season with a tractor on a quarter-section field. This is based on wheat yield of 30 bushel per acre wheat and a price of $5 per bushel.
Rear tire width
Dollar cost of loss 18 inch
We’re all used to seeing those arrow-straight sprayer
tracks through stands of grain in fields across the prairies. The widespread use of GPS has minimized the number of tracks in a field now that growers can work to a high precision and minimize overlaps, but the tracks are still there. And producers aren’t getting any grain production in those spots.
Overall, the total area of tire tracks in a field seems pretty small. But is it? Just how much production is lost due to tire tracks from sprayer passes? Specialized replacement tires for tractors minimize the amount of crop trampled by a tractor pulling a sprayer. And there are specialty manufacturers that make conversion wheel kits to install them on nearly any tractor model. But, can producers really save money by investing in a set of these narrow tires for crop spraying?
To answer that question there are a few costs to consider. First, like nearly every component these days, converting the wheels on a tractor isn’t exactly cheap. And it will also be necessary to spend some time making the change over.
Greg Setter runs Setter Manufacturing in Russell, Man., a company that specializes in tractor conversion. He says you’ll likely pay $3,600 to $5,000 for a set of rear wheel rims to equip a two-wheel drive tractor. Then there is the expense of the tires on top of that, which can run as high as $4,000 per pair of 9.5 by 48s.
DOING THE MATH
To see if going this route makes financial sense, you need to know just what kind of production is lost. Using a quarter-section field as an example makes for a good place to start. At half a square mile, the length and width of the field is about 2,640 feet.
The width of the tractor’s existing tires will determine the overall area trampled. Since 18-inch rear tractor tires are pretty common, calculating the area trampled by a set of them makes for a good benchmark. But boom width will really make a difference in the numbers, too, so let’s consider two sizes, 60-and 100-foot widths.
A tractor spraying a quarter-section field, with 18-inch tires pulling a 60-foot boom will trample about eight acres. Pulling a 100-foot boom, that number drops to 4.8 acres. Assuming a 30-bushel-per-acre crop of wheat at $5 per bushel, that means a production loss of $1,200 on the 60-foot boom and $720 on the 100 foot.
Using the same tractor equipped with special 9.5-inch rubber, those numbers drop significantly. The area trampled becomes 4.2 acres on a 60-foot boom and 2.5 acres with a 100-foot boom. The dollar losses plummet, too. It means a $630 loss on 60 feet and only $375 for a 100-foot boom. Spread that over your whole farm and, clearly, there are some serious gains to be had by making the change to narrow rubber.
“The payback (after converting to narrow tires) should be the same year,” says Greg Setter. But Setter says producers shouldn’t try to gain under-body clearance by significantly increasing the diameter from the tractor’s original tires. Using that method could lead to trouble.
A WARNING ABOUT TALL WHEELS
Setter says significantly taller tires, if you can fit them under cab fenders, could increase the torque load on the tractor’s driveline. And that might create stresses beyond the manufacturer’s original design specifications. “Where the problem really comes in is on hydro drives. You can overload those orbital motors,” he says.
But if you want to spray in mature crops, companies like Setters make under-body shielding that allows tall crops to pass smoothly under a tractor body to minimize shelling and other crop damage. With this kind of shielding, Setter says damage is minimal, “Just as long as the heads aren’t hitting something sharp.”
And if high clearance on a budget is important in your farming plans, companies such as Setter’s also make conversion kits that transform self-propelled swathers into high-clearance sprayers. Converting them to narrow wheels will minimize their footprint and give you a machine that can easily navigate through mature crop stands without any major modifications. For information on conversion costs for both tractors and swathers, check out www.settermfg.com.
A set of narrow tires and rims for a tractor requires some investment. And if the tractor is going to be put to use for anything other than spraying, you’ll still need to keep the original wider tire set on hand. The narrower tires will provide limited pulling efficiency and increase soil compaction. The difficulty in changing back and forth isn’t likely to be high, depending on the model of tractor, but it will take a little time. “It’s more than a five-minute job,” adds Setter. But the potential increase in crop production is likely to make it a sensible one.
Scott Garvey specializes in writing about tractors and farm machinery technology for publications in Canada and Great Britain. He’s also a former affiliate member of the Society of Automotive Engineers (SAE). He farms near Moosomin, Sask.