The New Harvest of Mid-Sized Diesel Tractors

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Soil type, and even local climate, may influence your choice, too. You'll need more traction in dry sand and sandy loam than in dry clay soil ... while wet earth demands more "grip" than does dry. These considerations might warrant the choice of a heavier tractor than would be needed on a farm without traction problems ... and could even make optional four-wheel-drive capability worthwhile.

ENGINE LUGGING ABILITY: Lugging ability refers to the capacity of an engine to maintain its pulling force during a momentary overload, and this is where diesel units prove themselves to be "naturals" for tractor work. At normal speeds of 1,500 to 3,000 revolutions per minute (RPM), the torque of a diesel (the twisting force developed by the engine)-unlike that of a gasoline powerplant -actually increases as its RPM drops. In other words, when a diesel tractor encounters a hill-or when the baler working along behind it takes an oversized bite of hay the machine just chugs along with minimal loss of power, while a gasoline engine would slow and strain under the same circumstances.

With these general points in mind, I strongly recommend that—as your decision narrows down to one or two machines—you ask the salesman for a demonstration on your property before you buy. Most dealers welcome the chance to show what their equipment will do. So test the lugging ability on your hills—while pulling a moldboard or chisel plow—and note the machine's traction on both sod and cultivated soil.

EXERCISE YOUR OPTIONS

In the accompanying table I've compared the specifications of several of the best diesel tractors in the 20- to 32 horsepower range. These are by no means the only units to choose from, but they're all quality machines and offer a full range of the special features available in this weight and power class.

Although most of the "specs" in the chart are easily understood, there are several that might need clarification.

LIVE PTO: On most models in the 20- to 32 horsepower range, the power takeoff (PTO) at the rear of the machine—and, of course, the tractor's forward motion—will stop when the clutch pedal is depressed. With a live PTO, on the other hand, you can halt the tractor without interrupting power flow to the PTO.

The principal advantage to live PTO is that it allows you to start rotating the blades of a bush hog (or the tines of a rotovator) before you get the tractor itself underway. This reduces the initial load on the engine ... which would otherwise have to overcome the inertia of the vehicle and the implement at the same time.

Most hay balers, silage cutters, and combines require a tractor with a live PTO. From time to time these implements must be allowed to "clear" themselves before taking in more material, and the "live" option will handle-such a chore quickly and easily.

OVERRUNNINGCLUTCH: An overrunning clutch permits power to be transmitted in one direction only. Should the output side of the clutch start to turn faster than the input side (due to the "push" provided by a driven attachment), the clutch will automatically uncouple. This feature is built into the drive mechanism of the PTO-in most of the tractors summarized in the table-to prevent the backup torque of an implement (such as the heavy, swinging blades of a bush hog for "sample) from damaging the transmission or pushing the tractor.

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