Why are tractors rated in hp?

[carpenter383]

This question has prolly been asked before but I was wondering does anyone know why they rate tractors in horse power instead of torque? It seems like torque would be a more desirable rating than horse power since tractors are not designed to be raced.

 

[knute_m]

History has a lot of momentum - or is it torque, if we add a few twists to it?

Just think how long it is taking us to convert to metric from the English system -- a system that even the English don't use anymore.

For what it is worth:

RevSearch Engine Dyno; Torque vs Horsepower

How long was earth considered flat when compared to the time it has been considered round? Old habits and old ideas are hard to overcome.

 

[Wayne County Hose]

Engines are usually rated at their peak hp for mathematical reasons. I can build 2 engines with the same exact max torque but they could be like night and day in a machine. Horsepower is a function of torque and rpm so it is a more evenly universal judge of an engine's performance.

Look at it this way. A worked 500 cid gas engine and a light truck diesel can have about the same torque. Put each engine in the same type vehicle, and the 500 cid engine blows the doors off the diesel. The 500 cid engine has way more horsepower.

 

[RobertN]

This question has prolly been asked before but I was wondering does anyone know why they rate tractors in horse power instead of torque? It seems like torque would be a more desirable rating than horse power since tractors are not designed to be raced.

Partly, because most got their start from farm tractors. As tractors were replacing horses, the main interest was in how many drawbar HP a tractor had.

Most small tractors, like my compact Kubota, are not drawbar rated. They, like most other go by HP of the engine.

And, like most diesel's in light trucks, the interest, and comparison is in HP. Especially, when comparing a diesel pickup to gas pickup. for hauling, Torque is king. But, most of the public is used to HP numbers.

 

[skidoo]

I think Tractors are designed to do work. HP is simply a measure of work per unit time. Of course, sufficient torque is necessary to overcome friction and inertia. Torque and HP are both important. But, HP is a measure of how fast "X" amount of work can be done.

 

[Marlowe]

I think it's just a matter of what we are used to. Bottom line is we don't really care how much max hp an engine is capable of; we care about what it does for us, but the rating system we are accustomed to using at least gives us somewhere to start when comparing them.