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Tractor vs truck pulling ability

J

JohnV2000

Member
I am always confused by how a tractor, like a Farmall H, has a 2.5L 4 cylinder engine yet only produces 25 to 30 HP, whereas a similar sized car is at least 4 times that much horsepower. I get that the tractor runs at lower RPMs and is geared differently, but really, is a tractor that much less powerful?

If a truck, like an F150 with a V6 gas engine, and a tractor, like a Farmall H of M, were both trying to pull a giant log, which one would be better?

Thanks for helping me understand this,

John
 
It's all speed related, a tractor will pull a lot up to about 4-5 mph, a truck will pull a load at highway speeds. I think the force
necessary to move a load squares with velocity. Some people have put tractor engines in pickups, they work but the speed is limited, I
think there was a video posted just recently.
 
A tractor has weight, gearing, and traction
going for it. Horsepower numbers are also
a poor comparison. Torque is really what
makes it happen. That low tractor
horsepower number is also not flywheel
horsepower, as cars are commonly rated.
Tractor horsepower is rated as drawbar pull
or PTO load.
 
Drawbar pulling force has very little to do with the engine's horsepower. Given enough weight
for traction, suitable tires to put the force to the ground, and low enough gearing even a small,
low-powered engine can pull a huge load. The problem is that it won't be able to do it very
fast. A good example is an electric winch that can pull 10000+ pounds with a motor with just a
couple of horsepower. In order to pull a certain load at a certain speed, however, requires a
certain amount of engine horsepower. A tractor is designed to provide drawbar pulling force at
relatively low ground speeds so as a result the needed engine power is also relatively low. On
the other hand, road-going vehicles are expected to maintain speed up hills at 70-80 mph which
requires quite a bit of power. This large amount of engine power, though, doesn't mean the truck
will pull like a tractor at low speeds because it won't be able to get enough traction to make
anywhere near full use of the engine's potential. An engine is only making full power at wide
open throttle with the engine at the rated speed which for a car or pickup very rarely occurs in
normal use. On the other hand, a tractor engine is designed to produce full rated power non-stop
for hours on end. To allow for this type of usage the tractor engine runs at far lower speeds
which limits the amount of power it can produce.
 
It takes a certain amount of power to move a weight upward, or a log sideways. If the 150 was loaded with 1500
pounds, and had slicks on the rear wheels, and was on pavement, it would win. But it is not equipped as such. The
H with about 5000 pounds and most of it on the rear wheels when pulling, would take its time, but it's tractive
force and time allow it to move the log. Energy near equal, time different. Watt are power as is horse power.
Watt hours is horse power hours. Jim
 
Makes me think of the ad that GM put out back in the late seventies showing one of their trucks pulling a John Deere plow. Think it was a k20 with 400 V8 and a bit of cast iron weight in the box and obviously four wheel drive. I've got the ad saved here somewhere.
 
If You compare two engines that are the same like
say a 5.9 Cummins in a tractor or 5.9 Cummins In a
pickup the tractor will have ground speed in the field
gears of maybe 5 or 6 mph at 2000 rpm but the
pickup will go 70 mph at 2000 rpm . Just depends
on how it?s geared or take an Isx Cummins In a 4wd
tractor the same thing tractor can probably work
about 6 mph but the same engine in a semi can go
70 or 75 at 1900 rpm.
 
The real answer is GEARS. Tractors are geared so much lower than cars and trucks that they have a tremendous mechanical advantage.

Look into the six simple machines - like the lever, screw, pulley, wedge, inclined plane, and wheel and axle. One renaissance scientist said that given a large enough lever and a fulcrum, he could move the world. Same principles apply here.
 
There is a certain maximum horsepower per cubic inch ratio that can’t be surpassed in a hard working engine without a combustion heat related problem. I’m guessing it’s something less than 1/2 hp per cubic inch. Seems like the new diesel tractors today are raising that ratio and half way getting away with it. A certain piston speed can’t be surpassed in a working engine because of the cooling transfer speed from the piston into the liner and then into the cooling system. This is engines that don’t shoot oil into the underside of the piston. Maybe someone who knows more about this than me can correct me if I’m wrong.
 
A working tractor is able to produce 100% of it's rated horsepower for thousands of hours, YEARS, working steady for eight or ten hour days.

While a fancy pickup "may" have 400 to 600 engine horsepower, how long do you think it would last if pulled to that capacity all day long, for days on end?

What HP does it take for even a BIG pickup to cruise along at highway speeds?

I've seen some numbers in the past, and my memory isn't good enough to quote 'em, but they are FAR less than the 400 to 600 HP the engine may be capable of.
 
Comparing the F150 to a Farmall, if the F150 were a 4x4 with low range, and you could put the power to the ground, it could easily pull as much or more than the Farmall.

But looking at the big picture, it couldn't do it over and over or pull the same load all day, day after day. It would soon stress the engine, frame, suspension, and drive train to the breaking point.

As for engine differences, an automotive engine is typically a high compression, short stroke, big bore, big valves, lots of valve overlap, light flywheel, light block, gets it's best power up around 6000 RPM, and rarely runs in that range. Good thing too, cause it wouldn't last long doing that!

A tractor, or industrial engine is low compression, long stroke, small bore, small valves, very little valve overlap, heavy flywheel, heavy block, gets it's best power around 1500 RPM, and is designed and governed to do that for many, many hours under the worst of conditions. Then rebuild it, and do it again!
 
(quoted from post at 17:48:28 01/16/19) I am always confused by how a tractor, like a Farmall H, has a 2.5L 4 cylinder engine yet only produces 25 to 30 HP, whereas a similar sized car is at least 4 times that much horsepower. I get that the tractor runs at lower RPMs and is geared differently, but really, is a tractor that much less powerful?

Yes, the Farmall tractor has that much less power than typical car or truck. The tractor is designed to pull heavy loads but at low speed. Therefore, it does not need the power of a car or truck which must operate at much higher speeds.

Consider:

1) [Work = Force x Distance] From this equation we see that a force does no work until it causes motion. But more to your question is the equation below.

2) [Power = Force x Distance / Time] Since Distance / Time = Speed we can substitute Speed into the equation. We have, [Power = Force x Speed].

Now lets use the equation: Lets say the tractor can pull a log comfortably at 4 MPH. The force to pull the log remains constant as we increase the speed, assuming no wind resistance. To pull the log at 40 MPH would require 10 times the HP. From this you can see the old H is going to run short of HP at the higher speed.


"If a truck, like an F150 with a V6 gas engine, and a tractor, like a Farmall H of M, were both trying to pull a giant log, which one would be better?"

The tractor is made to pull heavy loads. Really, why would one think a pick-up truck would be better for this task?

Thanks for helping me understand this,

John
Click to expand...
 
You left off the last half of your first sentence - " . . . in a certain amount of time". Without a time factor we're only dealing with a unit of force, not a unit of power.
 
(quoted from post at 17:48:28 01/16/19) I am always confused by how a tractor, like a Farmall H, has a 2.5L 4 cylinder engine yet only produces 25 to 30 HP, whereas a similar sized car is at least 4 times that much horsepower. I get that the tractor runs at lower RPMs and is geared differently, but really, is a tractor that much less powerful?

If a truck, like an F150 with a V6 gas engine, and a tractor, like a Farmall H of M, were both trying to pull a giant log, which one would be better?

Thanks for helping me understand this,

John
Click to expand...

When I was a kid working on my neighbors farm, something that I did a few times each summer was to pull two hay wagons to one of his other farms behind his Ford 841 with loader and Elenco FWA. It was all straight forward until I would come to a short steep hill on a short-cut street in town. I would charge at it full throttle, but it would slow me down rapidly and I would have to push the clutch in and stand on the brakes and put it down into third in order to climb the hill. There was plenty of power in the lower gears but not in 4th. The gearing was too tall.
 
This reminds me. Does anybody remember the TV commercial where either a Chevy or GMC truck pulled a 6 bottom plow with one of their trucks? I think that was back in the 70s. There was also an ad in the Farm Journal and/or Progressive Farmer magazines showing that truck.

Does anybody remember the fine print at the end of the magazine ad? It told all the special equipment that was on that particular truck. LIke a 3/4 or 1 ton chassis, 454 engine, heavy duty cooling, oil cooler, 4x4, heavy duty suspension, transmission, etc.

And that was just for a TV commercial. There is NO way it could do that day in or day out.
 
Another comparison is the 350 GM V8 that must have powered millions of GM cars and trucks over the years. I ran that same engine in a 1976
Massey 510 combine for years too. Not sure but I think the combine engine was rated about 120 hp but I could be out on that. It was governed
to run at around 2400 rpm and it did all day long for many years. Probably much the same rpm as your GM pickup cruising the highway at the
speed limit or more. Depending on the year and optional equipment that pickup engine likely was rated between 150 and 200 hp. Not sure what
point I was trying to make here. Just an interesting comparison of the same engine in two quite different work situations.
 

Gearing is the answer. Also the truck if it has an automatic transmission, the torque converter gives it a boost as the torque converter has a built in torque multiplication factor:

https://www.hotrod.com/articles/ccrp-0310-torque-converters/

Tractors are the answer for low pulling speeds. I’ve never understood why tractors are rated by horsepower instead of torque...

Horsepower is simply a number made up through a mathematical formula whole torque is actually the twisting force measured at the cranckshaft... torque is a much more useful number and occurs in higher numbers atmoower rpms.

HP and torque will always be the same at 5252 RPm due to the mathematical formula for HP. Only tractor engines are governed way lower than that, so HP numbers will always be lower. But torque is what moves the tractor and spins the implements.
 
Several years ago there was a fellow
that would bring an allis Chalmers
wd45 to the tractor pulls that had
one of the early GM diesel auto
engines in it. ( yes, the converted
350 gas) . Don't remember the
horsepower rating on those but sure
it is more than the output of the
farm stock tractors. Same
transmission and rear end. Tractor
with tractor engine would spin out:
gm diesel would power out. ( just
food for thought).
 
The reason that engines are rated by power instead of torque is that torque by itself does
nothing - it has to be delivered at some rate to accomplish work. Without a unit of speed (rpm
in this case) to go along with it the torque value gives no indication of the ability of the
engine to do work. When you multiply the torque value by the engine speed you have power and
that is the only usable figure to rate the engine's work capacity - there's nothing "made up"
about it. (Besides, torque is a force multiplied by a distance so it is just the result of a
mathematical equation too.) Torque is easily manipulated through gearing so the engine's torque
rating is essentially irrelevant since you don't do work right at the flywheel. The maximum
amount of wheel torque (where the work is actually done) at any given vehicle speed will occur
when the gearing allows the engine to run at its power peak, not the torque peak. This is why
the engines in tractors and all other vehicles are rated by power as it is the single value that
gives a complete representation of work capacity.
 
Simple High School physics question.
Power = force times speed.
Tractor's gear ratio slows the speed.
Lower the speed you increase the force(pulling
ability)
Didn't you cover that in HS?
 
(quoted from post at 22:50:29 01/16/19) Makes me think of the ad that GM put out back in the late seventies showing one of their trucks pulling a John Deere plow. Think it was a k20 with 400 V8 and a bit of cast iron weight in the box and obviously four wheel drive. I've got the ad saved here somewhere.
Click to expand...

Willys used to build a Jeep called a Farm Jeep that was intended to pull a plow, even could be had with a 3 pt hitch. Look at any old Willys CJ and note the rear bumper is a drawbar with lotsa holes in it. Designed for pulling things like plows.
 
(quoted from post at 20:47:56 01/16/19) The reason that engines are rated by power instead of torque is that torque by itself does
nothing - it has to be delivered at some rate to accomplish work. Without a unit of speed (rpm
in this case) to go along with it the torque value gives no indication of the ability of the
engine to do work. When you multiply the torque value by the engine speed you have power and
that is the only usable figure to rate the engine's work capacity - there's nothing "made up"
about it. (Besides, torque is a force multiplied by a distance so it is just the result of a
mathematical equation too.) Torque is easily manipulated through gearing so the engine's torque
rating is essentially irrelevant since you don't do work right at the flywheel. The maximum
amount of wheel torque (where the work is actually done) at any given vehicle speed will occur
when the gearing allows the engine to run at its power peak, not the torque peak. This is why
the engines in tractors and all other vehicles are rated by power as it is the single value that
gives a complete representation of work capacity.
Click to expand...

Brendon-KS,

Excellent explanation of torque versus horsepower, My compliments.

Ken
 

Also, keep in mind that the horsepower of a Farmall H is measured at the PTO. The horsepower of any car or truck is measured at the crankshaft. Horsepower is lost through the transmission and differential to the point that actual horsepower getting to the ground is MUCH less than rated horsepower measured at the crankshaft.

Also, when reading those inflated horsepower figures for a car or truck, take note of the RPMs required to achieve that power. Most often the RPMs are in the 3,500 and above range.
 
(quoted from post at 21:16:08 01/16/19) A working tractor is able to produce 100% of it's rated horsepower for thousands of hours, YEARS, working steady for eight or ten hour days.

While a fancy pickup "may" have 400 to 600 engine horsepower, how long do you think it would last if pulled to that capacity all day long, for days on end?

What HP does it take for even a BIG pickup to cruise along at highway speeds?

I've seen some numbers in the past, and my memory isn't good enough to quote 'em, but they are FAR less than the 400 to 600 HP the engine may be capable of.
Click to expand...

Not saying there are very many pick up engines out there that will hold up to your criteria of;

"how long do you think it would last if pulled to that capacity all day long, for days on end"

Here is some info on the GM 8.1l in my 1-ton.

(After extensive analysis of competitors' engines, the 8.1L development team set a goal of 200,000 miles of useful life without major repairs--and then achieved it. The engine has been tested and validated to meet this 200,000-mile durability standard. Before it was ready for production, the 8.1L had to pass the ``Marine Dock'' test, in which it is run at full throttle for 300 consecutive hours, and a minimum of 1000 hours at full-throttle operation for truck applications.)

Might be a hard test for some tractors to pass now days.
 
Kinda like my Farmall Regular which is rated at 13 hp, and my lawnmower has 16 hp. Lawnmower cant pull a 2 bottom plow though !
 
Brendan has the most complete/accurate answer of the bunch.

People have a really tough time understanding these concepts. I remember in grade 9 the teacher of the shop class where you tear down a briggs engine explaining it over and over to us trying to get everyone to understand.
 
You talking about the Jeep made me remember years ago we had an elderly gentlemen that lived a few miles
from us that plowed and worked down 10 acres with a old jeep.
 

Another major factor is stroke of the motor. Longer stroke delivers more torque. Examples are the old Farmalls had very long stroke while the old Fords were much shorter, so the Fords worked at higher RPMs. Another example is two old Ford motors. The 300-6 which was long stroke and the 302 V8 which superseded it. I had a heavy built 1981 Ford E-250 with 300-6 that would pull a heavy load up steep hills pretty nicely. I traded that for 1986 E350 with a 302 V-8. That 350 with the same load would die on the hills that the older truck did well on.
 
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