Pull from the front or the rear?

[LouNY]

The statement about if you have power and traction and the pulled load exceeds your tractors pulling capacity is just plain wrong

If you are pulling from a drawbar below the rear axle the front will be forced down not up

Draw the force vectors

We did hundreds of times in engineering school

Up violates the laws of physics

Andy

It is not wrong, I have seen it happen, I have had it happen.
You can draw all the force vectors you wish too,
when you start to calculate the rotational torque applied to the wheel and hub as compared to the front end weight and a drawbar that does not stick out beyond the outside of the tires we can discuss this again,
till then you are just plain incorrect.

Lou

 

[Threepoint]

Seems to me the nose of the trailer is going to exert downward force if its brakes are locked, regardless of up/down slope.

Haven't you seen the nose of a car drop when the brakes are applied? You think the nose wouldn't drop if driving uphill? Trying to pull a trailer with locked brakes is the same physics. It's not (primarily) the CG moving forward from the axle (or back as you say), it's the forward force exerted at higher elevation than where the tires grip the pavement and are trying to resist motion.

A tractor pulling a trailer is not like a car at all. You really do need to work on vectors and resolution of forces.

With suitable linkages in an "automobile: suspension, You can get the body to rise on deceleration and bank when rounding corners instead of rolling.

Comparing apples to pickles is not a wise thing to do.

Have to agree with California on this, and I don't doubt that he understands vector forces. I think you guys are talking at cross purposes here because of different assumptions. Tell me whether this reasoning makes sense: When you apply the brakes to a car (or tractor) moving without a tow, its forward momentum, inertia, causes rotation around its center of mass, which is likely above the axles. This translates into vertical ground reaction forces that cause the nose to dip. For the same reason, if the brakes of a trailer under tow were somehow to lock up before the brakes of the tow vehicle (e.g., from an electrical malfunction), the front end of the trailer would dip initially. This assumes of course that the center of mass of the trailer is above its axles, which is pretty safe, especially with a payload. For that few moments, as with a car/tractor, the trailer's rotational force around its center of mass translates to vertical ground reaction forces that momentarily cause the hitch/drawbar to dive, possibly even causing the front of the tow vehicle to rise.

HOWEVER, this is only momentary, as the continued forward momentum of the un-braked tow vehicle then meets the rearward braking forces of the locked trailer wheels. That forward force immediately overtakes the downward force on the hitch/drawbar. And that is where the height of the hitch/drawbar or other attachment point relative to the tow vehicle's center of mass becomes very important. Height of the drawbar (or hitch) of the tow vehicle relative to its center of mass will affect the amount and even direction of rotation around its C of M. If below the axle of the tractor, the rear wheels are likely to unweight and lose traction (unless the towed load is pulling from well below, as in my example of a truck in a ditch). By contrast, if well above, as with a chain attached to a raised 3-pt drawbar, or looped over a raised implement, the tractor might even flip over backwards.

 

[California]

I think that's valid.

The physics I was thinking about for a trailer with locked brakes - moving or not, is:

the tire footprint is the 'hinge point' and any forward pull on the hitch is going to have a forward and a downward component as the stresses hinge around that tire contact point.

I expect pulling that locked-brake trailer with a rope would illustrate this.


Added after thinking about this some more: the stress pulling a trailer with locked brakes is going to diagram as a diagonal line downward from the hitch to the tire footprint. I'm not a pro with vector diagrams but I think you can represent this as a horizontal force and a smaller vertical force, both starting from the hitch.

 

[RickB]

It is not wrong, I have seen it happen, I have had it happen.
You can draw all the force vectors you wish too,
when you start to calculate the rotational torque applied to the wheel and hub as compared to the front end weight and a drawbar that does not stick out beyond the outside of the tires we can discuss this again,
till then you are just plain incorrect.

Lou

I知 with you, Lou.

 

[RickB]

It is not wrong, I have seen it happen, I have had it happen.
You can draw all the force vectors you wish too,
when you start to calculate the rotational torque applied to the wheel and hub as compared to the front end weight and a drawbar that does not stick out beyond the outside of the tires we can discuss this again,
till then you are just plain incorrect.

Lou

I agree with you, Lou.

 

[boomer1025]

They are NOT DRAW BARS, They are spreader bars. Made for spacing the lift arms when no attachment is fitted.

That people call them draw bars, or use them for "pulling", is testimony to human ignorance.

I have one that stays on the tractor just about all the time, has a trailer ball in the center hole I use to pull my trailer around. It also can carry rear weight when needed using the loader. Also use it to pull small sawed up lengths of trees. Comes in very handy.

CountyLine Cross Drawbar, Category 1, 3/4 in. dia. at Tractor Supply Co.

 

[bcp]

It is a drawbar, or Ford was misinformed.

Here are some clips from the 8N manual. Ford calls it the fixed drawbar, and diagrams always have drawbar stays installed to keep it at a set level. They even have a section about using the holes to offset the implement, and how it affects the handling.

Bruce

 

[WranglerX]

I have one that stays on the tractor just about all the time, has a trailer ball in the center hole I use to pull my trailer around. It also can carry rear weight when needed using the loader. Also use it to pull small sawed up lengths of trees. Comes in very handy.

CountyLine Cross Drawbar, Category 1, 3/4 in. dia. at Tractor Supply Co.

View attachment 572137

Yep....

What Category 3 Point Hitch Do I Have?

Dale

 

[CalG]

Yep....

What Category 3 Point Hitch Do I Have?

Dale

I think you will find that today, John Deere calls it an "implement bar".

Lawyers being what they are.

They are not meant for pulling maximum loads that might lodge against immovable objects. The draw bar IS!

Only a fool would use terminology to justify stupidity!

 

[redman135]

Hello strantor. I only had time to read the first 3 pages. At Ag college this exact senario was demonstrated. Pulling off the drawbar (mounted under the axle) the tractor can rear up, BUT there is a point where the the pull on the drawbar is PREVENTING the tractor from flipping all the way over backward. This same pull is what caused the tractor to rear up in the first place.
The tutor also made the point that from the operators seat it is scarey and most people will hit the cluch and drop the nose back to the ground and blow a tyre or break the front axle.
"and USE the flaming SEAT BELT" (tutors last word in that class)
We were also shown a film of how quickly a tractor pulling from the top link mount point WILL flip over.
Hope this helps.

 

[JohnBuffaloMN]

Hello strantor. I only had time to read the first 3 pages. At Ag college this exact senario was demonstrated. Pulling off the drawbar (mounted under the axle) the tractor can rear up, BUT there is a point where the the pull on the drawbar is PREVENTING the tractor from flipping all the way over backward. This same pull is what caused the tractor to rear up in the first place.
The tutor also made the point that from the operators seat it is scarey and most people will hit the cluch and drop the nose back to the ground and blow a tyre or break the front axle.
"and USE the flaming SEAT BELT" (tutors last word in that class)
We were also shown a film of how quickly a tractor pulling from the top link mount point WILL flip over.
Hope this helps.

Thanks redman135. Wonder why there aren't automatic seat belts for a tractors?

 

[Threepoint]

I think you will find that today, John Deere calls it an "implement bar".

Lawyers being what they are.

They are not meant for pulling maximum loads that might lodge against immovable objects. The draw bar IS!

Only a fool would use terminology to justify stupidity!

CalG, why the last sentence? When someone has to resort to personal insults in a discussion, I figure they've already lost the argument.

In fact, the use of terminology is precisely what your exchange was about. In your post #52 you said:

They are NOT DRAW BARS, They are spreader bars. Made for spacing the lift arms when no attachment is fitted.

That people call them draw bars, or use them for "pulling", is testimony to human ignorance.

No one in this thread has claimed they are "meant for pulling maximum loads that might lodge against immovable objects." But they are certainly "drawbars", not for spacing the lift arms, and the holes across their length are intended to receive clevis hitch pins and trailer balls.
CountyLine Cross Drawbar, Category 1, 3/4 in. dia. at Tractor Supply Co.

I've had one for 25 ys, bought as a cross drawbar from Central Tractor Farm and Country back before they went Ch. 11. Also have the accessory called a "drawbar lock" that locks it to the lift arm to keep it from rotating in the ball ends. That, too, is still sold under that terminology today. CountyLine Drawbar Lock, Cat 1 at Tractor Supply Co.

Very handy to move trailers and equipment. I don't use it these days because my tractors have Harbor Freight quick hitches, and I haven't taken the time to figure out a way to lock the bar in position on a quick hitch to use the trailer balls. I'm kinda hoping one of you smart TBN members will come up with an easy solution.

 

[California]

... my tractors have Harbor Freight quick hitches, and I haven't taken the time to figure out a way to lock the bar in position on a quick hitch to use the trailer balls. I'm kinda hoping one of you smart TBN members will come up with an easy solution.

Here's the solution I've used for several years to pull a light (2600 lbs) watering trailer over rough disced ground. The small plates are welded to the standard adapter sleeves used with that hitch, and the more massive weld bead (rather than the plate) bears most of the rotational force. The plate/sleeve devices are bolted on, inboard as visible here and also through the outer holes that were intended for the clevis pin.

Several years use now, no problems. I don't recommend this for a trailer heavier than how I use it.

 

[WranglerX]

CalG, why the last sentence? When someone has to resort to personal insults in a discussion, I figure they've already lost the argument.

In fact, the use of terminology is precisely what your exchange was about. In your post #52 you said:




No one in this thread has claimed they are "meant for pulling maximum loads that might lodge against immovable objects." But they are certainly "drawbars", not for spacing the lift arms, and the holes across their length are intended to receive clevis hitch pins and trailer balls.
CountyLine Cross Drawbar, Category 1, 3/4 in. dia. at Tractor Supply Co.

I've had one for 25 ys, bought as a cross drawbar from Central Tractor Farm and Country back before they went Ch. 11. Also have the accessory called a "drawbar lock" that locks it to the lift arm to keep it from rotating in the ball ends. That, too, is still sold under that terminology today. CountyLine Drawbar Lock, Cat 1 at Tractor Supply Co.

Very handy to move trailers and equipment. I don't use it these days because my tractors have Harbor Freight quick hitches, and I haven't taken the time to figure out a way to lock the bar in position on a quick hitch to use the trailer balls. I'm kinda hoping one of you smart TBN members will come up with an easy solution.

Ummm.... Sort of a universal fix for the object of discussion when using QH....



Would also leave a selection of holes in "that thing" available to attach something...

Dale

 

[Threepoint]

Here's the solution I've used for several years to pull a light (2600 lbs) watering trailer over rough disced ground. The small plates are welded to the standard adapter sleeves used with that hitch, and the more massive weld bead (rather than the plate) bears most of the rotational force. The plate/sleeve devices are bolted on, inboard as visible here and also through the outer holes that were intended for the clevis pin.

Several years use now, no problems. I don't recommend this for a trailer heavier than how I use it.

Very clever! Thanks for posting! :thumbsup:

 

[Threepoint]

Ummm.... Sort of a universal fix for the object of discussion when using QH....

View attachment 572172

Would also leave a selection of holes in "that thing" available to attach something...

Dale

Dale, thanks! I like it.

Two solutions within an hour! :salute:

 

[CalG]

except for the reliance on the roll over bar and seat belt,

I seems you know what you are doing.

IIRC this thread started with the question about pulling from the front.