Tractor Horsepower Explained

Here we help cut through the hype about engine power to find the size that’s right for you.

By Oscar H. Will III

A lot of folks think that all they need to know about purchasing a tractor is how much horsepower, but that, in a sense, is putting the cart before the horse. What the prospective buyer should do instead is list what he/she actually needs and wants to do with the machine and let that help determine the power needed. More horsepower than you need costs more to purchase and to operate. Less horsepower leads to frustration and, quite possibly, damage if you try pushing your machine beyond its limits; or even unable to perform the task at hand.

Manufacturers often compete with one another by bragging that their tractor has the highest horsepower in its class. That’s potentially useful information if you need the power, but marketing hype nonetheless. In many of these advertisements, mention of which measure of horsepower is often overlooked, or, at most, relegated to a tiny footnote.

What you need to know about horsepower is that the engine provides the power and that some of that power is used up running the tractor’s accessories and operations. The unencumbered engine might make 100 HP at the flywheel at a specific rpm value. Set that engine into the tractor and hook up the hydraulic pump, transmission, alternator, air-conditioning, power steering pump, and even with the tractor running but parked, there will be less than 100 HP available to perform the work you require. There will be even less available when operating the loader and driving the machine. So, while the engine horsepower value is useful to a point, there’s a more meaningful number: the power takeoff horsepower (PTO-HP).

Horsepower at the PTO is generally based on a measurement with the engine set at the speed that turns the PTO at either of the standard speeds of 540 or 1,000 rpm. Also, know that some tractors create more PTO HP than others so you may not need to purchase as large of tractor to do the same job. This measure is more useful to you as a new tractor buyer because it lets you know how much energy your tractor has for running PTO-powered implements such as mowers, balers and augers. Your dealer and a quick Internet search can help you understand what PTO-horsepower you need to satisfactorily operate the implements you wish to employ at your place.