Pull from the front or the rear?

[CalG]

When we were clearing the land for my house I had cut down a group of 3 trees. These 3 trees were down a 50 degree slope. I had I use both of my hands to assist climbing up this slope to get to the tractor on dead flat level ground. I had hooked all 3 trees together for the pull. These were not real big trees, maybe 8 inches in diameter. So I attached them to the immovable drawbar. My father in law in his 60 hp tractor with no FEL but had weights on the front (used this tractor for bailing) started to pull. In what seemed like a split second the front end shot up. He quickly pushed in the clutch and it dropped back down. He absolutely would have went over if he didn稚 push in the clutch.

Yes, Do a little "vector drawing", of where that hitch line crosses the rear wheel axle centerline.
Likely very high! /-O
ohh ohh!

 

[jdorenbosch]

While the draw bar is as stated above, either direction can lead to a wrecked tractor and maybe a dead driver.

When it flips over backwards it is due to using too much acceleration with good traction from the rear tires on a non movable object. Even using the draw bar will not prevent it from happening. Many a tractor pulls have ended that way.

The same could happen when pulling from the front, but it would be harder.

It does not matter whether the point of attachment is above or below the axle. It matters how high it is above the ground. Lower is better. The drawbar pulls backwards and the bottom of the wheel pulls forward. This produces a torque on the tractor that could flip it over backward. Next you have to know where the center of gravity is of the tractor and the tractor's total weight. Then do the math or do the experiment. With a little luck the wheels will slip before the tractor flips backwards.

 

[RaydaKub]

The forces would be extreme. But you don't need vector analysis to imagine the scenario where the rear axle can't move forward (due to the drawbar chained to an immovable object) and a mechanical driveline continues to send torque to the rear axle that has perfect traction. If nothing breaks then rotating the tractor up and over backward is inevitable. I suppose if the drawbar extended out beyond the tires and didn't bend then the rotation would end when the weight of the tractor rested on the tip of the drawbar so the tires lost traction.

I don't think this completely accurate. At the point where the nose of the tractor is straight up in the air, the drawbar has rotated down. Since it starts below the axle, we have now rotated it further below, but also in front of the axle the same amount that it would hang below the axle normally. The object is immovable, but that distance had to come from somewhere. The traction is perfect, so it didn't come from slipping the wheels backwards. The chain presumably didn't stretch, either. However this also illustrates the position where the only place the drawbar can go to allow the wheels to move forward is to rotate backwards again and bring the front wheels back down. The only component left is the engine; my choice here is a stall.

This leads me to the conclusion that the scenario is contrived.

I haven't been to a tractor pull in a long time, but it seems to me that just about every tractor there either keeps the front wheels on the ground or they float a foot off the ground. Floating signifies to me the actively balanced situation that is a compromise between solidly on the ground and the nose straight up. As the torque brings the wheels up, the pull below the axle brings them back down.

 

[California]

Yes but ... I think in a real-world scenario the drive tires can hop and move backward. Then assuming nothing breaks, pouring torque into the ring gear will continue to 'climb the ring gear' and walk the tractor over backward if tire slip is insufficient. That torque has to go somewhere. Aside from tire slip, where else can it go?

I'll repeat a point I mentioned above - a friend told me his father became disabled when an old small crawler came over backward due to a trailer with locked brakes.

 

[kenmac]

The key here is traction. If something that is attached to the rear and gets stuck, etc, and the rear wheels get traction. I can see the tractor flipping backwards.
If the rear wheels spin, and the tractor sits there and spins the rears, I doubt it flipping over, but you never know if/when the rears may gain traction

 

[RaydaKub]

Yes but ... I think in a real-world scenario the drive tires can hop and move backward. Then assuming nothing breaks, pouring torque into the ring gear will continue to 'climb the ring gear' and walk the tractor over backward if tire slip is insufficient. That torque has to go somewhere. Aside from tire slip, where else can it go?

I'll repeat a point I mentioned above - a friend told me his father became disabled when an old small crawler came over backward due to a trailer with locked brakes.

Yes, vector analysis is very helpful to attempt to maximize your tractor's capabilities. Any of these assume constant pull, constant power, constant positioning, even constant weight. The problem is that none of the forces are constant. Wheels might grab on a rock, or the ground is more firm. The bounce of the front end might set off wheel hop. I used the term active balancing on purpose to try to describe it. Unfortunately, there are forces that we can't necessarily see or predict that throw the balance off.

 

[Automan45]

I haven't seen mention but typical chevron tread rear tractor tires are made to pull from the back. Pulling from front, the tread fills with soil and will stop gripping.

 

[kthompson]

I grew up in small farm country. Way before roll bar or front end loaders being common. It is basically flat ground but have plenty of ditches and branches to drop tire in. Have one person I knew who died when being drunk he rolled his tractor over sideways when wheel dropped off side of small hill in ditch. Have a friend who rolled tractor on it's side when he turned too short onto a road and dropped rear wheel in ditch. There were more accidents but the best I can remember none were with a tractor flipping over backwards. Have heard horror stories of years ago people chaining log under the tractor to the rear tires and driving tractor out of bog and the log coming around hitting and killing the driver.

Have seen many and I mean many tractors with the 3 pth drawbar mostly used to pull farm trailers especially tobacco trailers and you will like this one, logs for you would use the lift to pick the butt end up to clear the ground when pulling. Never heard of a tractor rolling over backwards even doing such dumb stuff. Right before Hurricane Florence hit us. Neighbor had construction trash bin full of trash that could have blown out damaging his house he asked if I could move. Needed to turn it around first so backed up to it with subsoiler on the 3 pth and used chain hooked short to the bin so could lift it so I could swing it around. Yes with lift fully raised my front end picked up to the point the front wheels cleared. Was I concerned about flipping a tractor over backwards, no. I was in low gear so tractor was not moving much above a creep and the subsoiler would also help prevent it flipping backwards (yeah I know a subsoiler is made to go into the ground but it also requires forward travel for it to) also was hooked very close to the trash bin which would have called roll bar is it had began to roll. N tother words I was in control. It was not hop on with no thought to what was doing and take off. The old farmers were not risk takers. For one thing they took care of their tractor and their equipment.

What am I trying to say? Being smart in what you are doing is very important. Speed kills as does not paying attention. I suspect with all the fel out there today more roll overs are caused by improper use of them than pulling from 3 pth drawbar. Now, for those who live and work on hills or mountains no way saying working on our grade is like your grade. There have been so many odd deaths with tractors and their implements it is amazing.

 

[MHarryE]

In theory, a pulling tractor should not be able to flip backward. In the tractor classes the drawbar can be no more than 20 inches above the ground and the pin 20 inches or more behind the centerline of the rear wheels. As the front rises the hitch drops and if vertical, the drawbar is on the ground so it will be unable to pull. There is still momentum to be considered - that’s why I said virtually impossible. In addition most pulls limit front tires to rise no more than 24 inches above the ground. If they do the driver gets a red flag and their pull is over.

A tractor will flip backward without a pull if the conditions are right. I had a near death experience in my teens. I let our Allis-Chalmers B roll backwards down a gentle slope with the clutch depressed to avoid shifting into reverse. When I had gone back far enough so I could make my turn, I popped the clutch. The front end came up so fast I couldn’t believe it, but in those days my reactions were lightning fast so I depressed the clutch and the front end crashed down. Fortunately it did not break the tractor in two but it did break the pivot bolt for the front axle. It’s one of those “Put the fear of God in you” experiences a person can never forget. So what did I end up doing as part of my career - investigating fatal accidents to determine if the cause was equipment failure or operator error.

 

[CalG]

All sorts of possibilities
Funny videos indian tractor pulling HIGH 2 - YouTube