Choosing the Perfect Tractor

Enlarge Image Image Gallery iStockPhoto.com/Michelle Junior

When Charles W. Hart and Charles H. Parr first coined the term tractor in reference to one of their petroleum-powered pieces about a century ago, they described a machine capable of easing the physical burden on farms of all sizes. Although the steel-wheeled contraptions that Hart-Parr Manufacturing Co. first offered bear little resemblance to today’s sleek, smooth-running machines, their early success was sufficient to provide the foundation for one of the longest-running and most recognizable symbols of modern agriculture.

In the early years, tractors had engines, drive trains (complete with clutches, transmissions and rear axles), stationary power drive systems (belt-pulleys and power take-offs PTOs), and a drawbar for pulling. Step forward a few years to the arrival of specialized hitches for mounted implements and hydraulic systems to raise and lower them, offering even more versatility. Today’s tractors are as fully evolved as our computer-controlled cars and trucks. On the surface, they still have most of their predecessors’ principal components. But those components have changed dramatically, and in many cases include two or more variations.

When shopping for a new (or recent-used) tractor, buyers choose more than just engine size and hitch equipment. There are no fewer than four discrete types of transmissions, at least three styles of tires and two drive systems to decide on, in addition to drawbars, hydraulic outlets, operator amenities, ballast and more. Making informed choices when putting together a new tractor or carefully choosing a used model is key to having a fully functional, enjoyable and safe farm power experience.

Horsepower with Bite

Tractor marketing pitches universally point to engine power to lure prospective buyers, but that isn’t the most useful number when trying to understand a machine’s capabilities. No one would ask a 25-horsepower lawn tractor weighing 750 pounds to do the same kind of work expected from a 4,000-pound, 25-horsepower farm tractor. A better measure of a tractor’s capabilities comes from drawbar and PTO ratings, which will be much higher for the farm tractor than the lawn tractor.
Although the value is different for each machine, most tractors offer between 75 and 85 percent of their engine’s power at the PTO, which is then available to run powered implements such as balers or mowers. The tractor’s drawbar horsepower, on the other hand, cannot be accurately estimated from engine power because it depends on the tractor’s weight, tires and traction characteristics. In the same operating conditions, the heavier of two otherwise identical tractors will have more pulling power, but tire patterns will also make a difference.