# Does one horsepower really = the power of one horse?

I was watching the Travel channel yesterday and they had a program about people that build monster trucks for tractor pull competitions. He boasted that he had four engines in his rig that generate 14,000 HP and can drag 60,000 pounds against the ground.

That was pretty impressive but I was thinking that if you really had 14,000 live, medium sized horses hooked up together somehow, you could do much, much better than that. Likewise, I don’t think a one horsepower motor would do very well powering a carriage with several people in it or plowing an uneven, rocky field. Horses have, and continue to do all of that.

I know the definition of a horsepower unit of measure.. What I want to know is how that compares to the work that an actual horse can do and why they choose the standard that they did?

They (they being one James Watt) chose the unit based on actual experimental results with real horses:

So, I’d say that, yes, one horse can output about one horsepower, on average.

It would be a great car commercial to strap (or just realistically animate) 300 horses to a chariot and race whatever SUV they are advertising

Maybe they’ve done it. I haven’t seen it.

I think 14,000 horses would have better traction than one monster truck so yeah…I’d expect they’d do better too. That does not mean however that 14,000 horses have more energy output…just better able to focus that output to a given task (assuming of course you could actually get 14,000 horses to pull in unison).

Well, it would be great advertising since the 300 horses still wouldn’t have a top speed much over 40 mph.

Why did he apply the half-a-horse correction factor? I’ve wondered that ever since I was little and read a trivia bit to the effect that one horsepower is actually 1.5 horses’ worth.

I believe it was to allow for frictional losses.

Agreed. In the OP, the (claimed) 14,000 hp is said to be capable of dragging 60,000 lbs - just over 4 lb/hp. I think a horse could do a bit better than that.

Another way to look at this is by means of the equation:
power = force * speed

Using this and assuming a coefficient of friction of 1.0 (that is, it takes one pound of force to drag one pound of weight), we can calculate that a 14,000 hp truck should be capable of dragging 60,000 lbs at a speed of 87 mph - obviously absurd.

I think we can conclude that the extreme power is needed to start the weight moving, and that traction is a significant issue.

Was this really a 14,000 horsepower engine? I don’t know much about truck engines but this seems an order of magnitude too big to me. Googling for semi tractors I can find a lot in the 300-500 horsepower range; four of these might make 1400 horsepower, but 14000 seems dubious.

Well, you need to remember that these are not your run of the mill truck engines. I can’t find any truck specific links right away, but here aresome tidbits from the NHRA. With 4 engines, each is putting out 3,500 hp. Doesn’t seem unreasonable.

Remember that in addition to moving the attached load, the horse has to move the horse, of course.

They were actually modified jet engines from a military helicopter. There were four of them on one rig. That was for the “unlimited” category. In lower classes, some people also used old souped up aircraft engines for less multi-thousand horsepower performance.

I seem to remember being taught that the measure of how much a horse could pull was for a particular horse in England. Wasn’t it something like the strongest horse then known?

OK. Guess I should have taken the description “monster” at face value…

At horse pulls the draft horses will pull two to three times their own weight (10000-12000lbs with two horses). The full pull is 14’, and the weight is on a flat-bottomed sledge pulled over sand. I don’t know what that works out to, but I’m pretty sure that’s more than 2hp those guys are putting out. Of course, they certainly couldn’t maintain that effort for any appreciable length of time.

doesn’t so many volts or ohms equal one hp? I remember hearing something about it in an intro to electrical circuits class once.

Watts are a power unit. 1 hp = about 750 watts. I’m too lazy to look up the exact conversion at the moment. Volts measure potential, ohms resistance. A watt is one ampere of current flowing across 1 volt of potential.

1 horsepower = 745.699872 Watts - I love google.

Back in the 1800’s when the old steam tractors were making their appearence, they were rated in drawbar HP. It is figured different today but as I heard it from old timers, they just kept hooking horses to the tractor and when the horses won the pull, they just subtracted one horse and you then had a tractor with 98 drawbar HP.

YMMV