Oil & Fuel Diesel Tractor HP vs. ATV or Car

[slowzuki]

Two kinds of power:

PTO Power - how much torque at a given rpm, limited only by your engines hp.

DRAWBAR Power - related to how much weight x how fast you can pull. This is limited by two things, your engine hp and also your drawbar pull which is a function of weight.


So heavy machines can generate high drawbar pull to move things. Once the drawbar pull is exceeded, the machine can't move. If it can't move, it can't make any drawbar power.

 

[RWolf]

This is how I look at it. It's very simplified and not completly acturate but here goes. If you have a 1hp motor it will require "x" amount of force to stall/stop it. If you pass that same 1hp motor through a 1:2 gear ratio setup your motor speed will drop by 1/2 but it will take twice the amount of force to stop it. That's why with my small 14 hp subcompact tractor running through 2 inline 3 speed transmissions both in 1st gear I have something like a 500:1 (give or take) reduction in speed (a snail can go faster) but "if" I could maintain traction I could pull a house down .

 

[slaveToHorses]

The real key differentiator here is the torque. Your ATV has very little of it and the 30HP tractor will have gobs of it. The torque, combined with the weight of the tractor and the diameter of it's wheels, when applied through the low gearing, makes it ideally suited for moving things on and through dirt. But not particularly quickly.

If you park the tractor on concrete and drop the clutch in first gear, at high throttle, the tractor will simply flip over backwards. It will rotate it's mass about the rear axle. Now that is torque. Don't try this at home!

 

[slowzuki]

The last two posters are confusing torque and hp with what is really being asked.

Torque can be muliplied by gearing. HP is HP. The curves are important when you get technical about it but if you are talking about moving things, your drawbar pull is the only thing that matters, and for that for small machines, just look at the weight.

A 2000 lb 20 hp antique tractor can't generate more than 2000 lbs of drawbar pull. A 2000 lb sports car with 600 rear wheel hp, can't generate more than 2000 lb of drawbar pull (well, a tiny bit more with sticky tires and good surface, but certainly not on dirt with tractor tires on it)

So they would be roughly comparable except the car isn't geared to go slow enough for working a plow, and the tractor isn't geared doesn't have enough hp to do anything but go slow.

 

[slowzuki]

If the two engines are rated at the same brake hp and you add the correct gearing to match speeds, and you compensate for the change in weight, YES they will pull the same in the test when operated at their peak hp.

In real life there are a few other items, as you can use the weight of the big dozers rotating engine mass to smooth out small blips that would stall a light atv engine. The diesel engine would have a very flat torque curve so it wouldn't stall if you slightly reduced RPM's. And there are a few other little technical items.

Left, if it is all about gearing, does that mean that if you put an atv engine (56 hp) into a tractor or bulldozer it would have the same power as a 56 hp tractor/dozer? Or is it a separate unit that is measured.

I did read wikipedia but I didnt really understand. It looks like hp is a measure of output over time so a higher rpm engine with less torch can put out more hp. I dont understand it.

 

[MessickFarmEqu]

Also keep in mind that a tractors rated hp can be maintained for long periods of time.. IE.. hours or days of running at max rated hp and rpm.

Take yer atv, tach it out to max rated rpm under heavy load.. I bet it's lifespan will be measured in units -LESS- than hours..

This is an important point. A car engine can crank loads of HP, but only runs at about 20% of its peak load capacity at most times. If you ran it at 100% for too long, it would blow up. A tractor runs at 90% of its peak capacity, so its de-tuned to withstand more rigorous use. Someone could probably crank 50Hp out of a BX.. but the engine would not last long.

 

[Egon]

I'm starting to wonder what breed of horse the first guys used to determine horse power. Was it a Percheron or a Belgian?

And then I get really confused when I realize either one could walk away with all 16 HP of my tractor! and not break into a sweat!

 

[MossRoad]

I'm starting to wonder what breed of horse the first guys used to determine horse power. Was it a Percheron or a Belgian?

And then I get really confused when I realize either one could walk away with all 16 HP of my tractor! and not break into a sweat!

Blame Mr. Watt. He is the guy that came up with horsepower and confused everything.

Did you read that article I linked to earlier? It has some great reading about torque, corvettes and water wheels.

 

[Z-Michigan]

Long story short - the stated ratings are basically accurate and, in terms of hp, the ATV may have it over a CUT, and any car certainly will. But to accomplish tractor tasks, the tractor engine is far more suitable. ATVs can do some mild tillage but are not well suited and even the smaller SCUTs will be better for any significant use.

I'm starting to wonder what breed of horse the first guys used to determine horse power. Was it a Percheron or a Belgian?

And then I get really confused when I realize either one could walk away with all 16 HP of my tractor! and not break into a sweat!

I think it was one of the draft horses of the time, most likely a predecessor of the Shire and/or Clydesdale (Watt was in England, ya know). And the rating contemplates that the engines run non-stop but horses need time to rest, sleep, and do various other horsey things. So the instantaneous pull of your Percheron might be a lot more than a 1hp tractor can do, but theoretically at least the 1hp tractor will get more work done in 30 days (running constantly) than the horse could. All another reason it's a highly imperfect scale.

 

[jmfox]

I recall the old Cat Taxcavator with 50hp that was unstoppable. It weighed 12 ton and the engine and transmission were huge. If you compare that motor to a 50hp motorcycle motor you should notice that the Cat has a more competent delivery system, positive even when the load pulls back. The motorcycle is like the guy who looks strong but can't give you a days work. They have the muscle but not the drive, like the Belgian.

jmf