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Discussion Starter #1
Hi all,
Does anyone know a way to calculate how much torque a tractor is producing at the wheels or axles? I'm curious how much all of the reduction amplifies the engine's output.
 

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On most tractors,
the maximum torque at the rear axle is meaningless because you can not get enough traction to use all the torque available,,,

So, if your tractor can pull a maximum of 3,000 pounds,,
and
the distance from the dirt to the center of the axle is 2 feet,,,

your tractor is producing (2X3000=6000) 6,000 foot-pounds of torque.

If the tires are spinning and the load is not moving, the torque could be anything,,,
 

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Hi all,
Does anyone know a way to calculate how much torque a tractor is producing at the wheels or axles? I'm curious how much all of the reduction amplifies the engine's output.
Probably easier to take it somewhere and put it on a Dyno. :)
 

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I can't help with that but I can show you how to calculate PTO torque, you might find interesting.....especially if you ever get the idea to step close to a spinning one:laugh: Screen Shot 2018-10-19 at 10.30.31 AM.png
 

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Discussion Starter #5
I know how to calculate torque coming out of the engine. But tractors amplify torque. Unlike HP, torque can be amplified almost infinitely by slowing things down with gearing, which is what tractors do. So a tractor that puts out 50 ft lbs of torque from its engine at the rated RPM might amplify that to some obscene number at the wheels. I'm really curious how much torque these things are actually putting to the ground.
 

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I know how to calculate torque coming out of the engine. But tractors amplify torque. Unlike HP, torque can be amplified almost infinitely by slowing things down with gearing, which is what tractors do. So a tractor that puts out 50 ft lbs of torque from its engine at the rated RPM might amplify that to some obscene number at the wheels. I'm really curious how much torque these things are actually putting to the ground.
IIRC, the theoretical value is simply the torque at the engine multiplied by the drivetrain gear ratio. So if the torque at the engine is 100 lbs/ft and the drivetrain in 1st gear is 32:1 then the torque at the axle is 3200 lbs/ft.

Of course, transmissions have losses. Unless you know that loss, you can't determine the actual value.

Al
 

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Discussion Starter #7
IIRC, the theoretical value is simply the torque at the engine multiplied by the drivetrain gear ratio. So if the torque at the engine is 100 lbs/ft and the drivetrain in 1st gear is 32:1 then the torque at the axle is 3200 lbs/ft.

Of course, transmissions have losses. Unless you know that loss, you can't determine the actual value.

Al
Is the drivetrain ratio included in tractor specs somewhere? I've never seen it. And does it include the rear tires into the equation?
 

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Is the drivetrain ratio included in tractor specs somewhere? I've never seen it. And does it include the rear tires into the equation?
a. I don't know. I'm sure the manufacturer knows it, but whether they publish it...?
b. The wheel diameter doesn't affect the torque. It does determine the tractive effort.

Al
 

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Torque also has to do with rotating mass. Case in point is the old flywheel engines. 6 hp engines weighed several hundred pounds and with those flywheels turning a robust 600rpm or less, they could move the world.
A lil Farmall Cub was like what..9 hp.I think a good judge of torque would be the drawbar test. If you look at actual tractor tests you will see hp, pto hp, drawbar hp and even belt hp.

Sent from my LGL52VL using Tapatalk
 

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Is the drivetrain ratio included in tractor specs somewhere? I've never seen it. And does it include the rear tires into the equation?
This only works for a true geared transmission, hydros are another story altogether, to figure out the gear ration of the transmission as a whole you simply divide engine RPM by rear tire RPM. That will give you the ratio.

So say you have an engine at 1800 rpm and a rear tire at 600rpm that would be 1800/600= 3. So you would multiply your rated engine output torque at 1800 rpm by 3 to figure out wheel torque.
 

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This only works for a true geared transmission, hydros are another story altogether, to figure out the gear ration of the transmission as a whole you simply divide engine RPM by rear tire RPM. That will give you the ratio.

So say you have an engine at 1800 rpm and a rear tire at 600rpm that would be 1800/600= 3. So you would multiply your rated engine output torque at 1800 rpm by 3 to figure out wheel torque.
There are gears in a hydro trans. You have a ring and pinion as in any differential, a set of range gears( high, low, medium, A B C D depending on model. Also some have final drive gears on left and right axles. Plenty of gears and ratios to choose from.
By pushing the pedal, more or less, on a hydro you are not changing any gear ratios. You are mearly increasing or decreasing pump flow, which equates to more speed, less speed.

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There are gears in a hydro trans. You have a ring and pinion as in any differential, a set of range gears( high, low, medium, A B C D depending on model. Also some have final drive gears on left and right axles. Plenty of gears and ratios to choose from.
By pushing the pedal, more or less, on a hydro you are not changing any gear ratios. You are mearly increasing or decreasing pump flow, which equates to more speed, less speed.

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You may not be changing “gear ratios” by moving the hydro pedal, but you are changing the ratios of the input speed vs output speed.
The JD have a fixed displacement motor, so you are right, the torque is constant (assuming max pressure is maintained), but the speed (and therefore the power) is varied as the pump displacement varies.
Kubota has a 2 position variable displacement motor as well as a variable displacement pump, so they can get a torque boost, with a corrisponding speed reduction (constant power).
The point is that hydrostatic transmissions do act very similar to gear drives.
 

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Quite right Arlen. They do act the same. What was that system IH had?? Torque amplifier or something?
You may not be changing “gear ratios” by moving the hydro pedal, but you are changing the ratios of the input speed vs output speed.
The JD have a fixed displacement motor, so you are right, the torque is constant (assuming max pressure is maintained), but the speed (and therefore the power) is varied as the pump displacement varies.
Kubota has a 2 position variable displacement motor as well as a variable displacement pump, so they can get a torque boost, with a corrisponding speed reduction (constant power).
The point is that hydrostatic transmissions do act very similar to gear drives.
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Quite right Arlen. They do act the same. What was that system IH had?? Torque amplifier or something?

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I Remember people referring to it as “the torque”...and *****ing allot when they went to hell:laugh:
 

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Lol yup. On a different note, I have a 2025R Gen 1 in the shop with a window punched thru the trans center case on right side. So.. A trans removal and complete teardown, center case replacement is on my list. Now we can all see how this hydro thing works. To include PTO, range box and differential. News and photos coming soon! Now back to our regularly scheduled programming.
I Remember people referring to it as “the torque”...and *****ing allot when they went to hell
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Lol yup. On a different note, I have a 2025R Gen 1 in the shop with a window punched thru the trans center case on right side. So.. A trans removal and complete teardown, center case replacement is on my list. Now we can all see how this hydro thing works. To include PTO, range box and differential. News and photos coming soon! Now back to our regularly scheduled programming.

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That will be great! I will be looking forward to it.
:bigthumb:
 
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