I had an epiphany

[sheepfarmer]

This is a good point!

Force pulling on the draw bar (it being below the rear axle) will cause the front of the tractor to be pushed down.

But as sheepfarmer says, if the rear wheels do not lose traction, a force lifting the front of the tractor will be developed by the engine power to the rear wheels.

IF the rotational force of the tires on the rear axle exceeds the force generated by the pull on the drawbar, which is below the axle, the front of the tractor will lift.

This must of been the situation that Skeets experieced.

Do not recall this ever being pointed out in safety literature I have read in the past, related to the reasons why using a drawbar is the safe way to pull something...

I think we have the answer to what Skeets experienced!

Added thought: As the front of the tractor lifts, due to the geometry, the force generated by the draw bar increases, so there is a bit of self correcting action that occurs, tending to oppose the lift of the front of the tractor...how much this help, no clue here...

As skeets pointed out above in tractor pulls the front end of a tractor can lift off the ground, so a hill is not critical to seeing the problem, but might make it worse.

 

[Henro]

As skeets pointed out above in tractor pulls the front end of a tractor can lift off the ground, so a hill is not critical to seeing the problem, but might make it worse.

I am pretty sure those tractors are driving the rear wheels only, and if so, they would want the front to lift off the ground a little, so all the weight would be on the rear axle for maximum traction.

There must be a bit of science/engineering involved with positioning of the draw bar so the tractor lifts the front wheels, but does not flip over backwards...

 

[NHSleddog]

Explains why the old tractor dad had would only pull a wheelie if I let it roll backwards down hill and dropped the clutch it wouldn’t do that on flat ground.

@NHSleddog can we get another picture please?

LOL - not a chance.

This is pure math and the answer is quite easy and has nothing to do with tractors or drawbars. But do a google on drawbar wheelies anyway.

The tractor pulls are a perfect example. And Henro, many tractor pulls are "factory" tractors with OEM drawbar as well as 4x4 - maximum traction is the name of the game. The lift is from the successful "maximum traction". Do a google on tractor wheelie bars.

Let me throw one thought out there and then let the math challenged try to explain around it.

Screw the drawbar. Go all the way UNDER the tractor and grab the front bumper, this SHOULD hold the front end down better than anything.

Now apply enough power/traction to the rear wheel and still watch the front end come up and the tractor flip over. If the object is unmovable and the tractor won't slip, something will break.

 

[Henro]

OK NHSleddog, I'll bite...LOL

Let me throw one thought out there and then let the math challenged try to explain around it.

I don't see any math in you example...

Screw the drawbar. Go all the way UNDER the tractor and grab the front bumper, this SHOULD hold the front end down better than anything.

Your cable exerts essentially no downward force on the front of the tractor. Nearly all the force is towards the back of the tractor.

Now apply enough power/traction to the rear wheel and still watch the front end come up and the tractor flip over.

Since your cable exerts no downward force (possibly a tiny bit, depending if it angles downward between the front tie point and tie point on the load being pulled) the tractor acts the same as if the cable is not there.

If the object is unmovable and the tractor won't slip, something will break.
.
OR (if lucky) the engine will stall before something breaks...