Pull from the front or the rear?

[CalG]

Wow. I can guarantee none of those dudes did any vector analysis. Half of them are pulling from well above the axle. At least one of them is dead for sure.

When BOTH are pulling high, Is there increased danger to either? **** vectors!

 

[CalG]

Does that analysis include the torque that the pinion gear is exerting against the ring gear?

Those Forces are COMPLETELY taken out internally. You know, Cast iron, with bearings and the like. The TIRE contact is the ONLY resolvable force. Don't get confused, The pinion cannot climb the ring! It can only apply a force. If not reacted upon by the TIRE contact, There is nothing....

 

[California]

So the tires will lose traction before the tractor is standing vertical even when the drawbar isn't long enough to reach the ground at any point? Seems to me the resistance to going over will lessen, not increase, as the tractor approaches vertical.

 

[CalG]

Tires losing traction is not in my play book. I'm not sure where that theme comes from.

What is wanted, is a lever arm that opposes the turning "torque".

Imagine a lever arm EXACTLY the same length as the tire Outside radius.
The tire turns one way, the lever arm opposes.

Could the tractor over turn by tractive forces alone?

No inertia etc.?

No! It could not.

 

[California]

So the tractor must stall (or strip gears etc)?

 

[gladehound]

When a tractor turns over backwards when pulling from a fixed draw bar below the rear axle, the axle of the tractor actually moves backwards (towards the immovable object) as the tractor rotates around the tires. The rear tires aslo roll backwards towards the immovable object. When this happens, it happens very fast because the tractor is rotating around the rear tires while the rear tires are rolling backwards so that draw bar (where attached to the pulling line) stays the same distance from the moving object as it moves down and forward with respect to the rear tires.

This can and does happen. I've seen it happen with a John Deere Model A. Big Ag tires, and a light front end (typical old field tractor design) makes it very possible to roll over backwards when pulling from the draw bar below the axle.

Small diameter R4 and turf tires and much more forward weight distribution make this scenario all but impossible with a modern CUT or SCUT.

Now if you pull from the top of the ROPS, you're likely to lift the front but it will lift very slowly so it's easy to react to. If you pull from the fix draw bar below the axle you are unlikely to lift the front and even less likely to roll over backwards, but if it does start to happen, it will happen very, very fast. To counter this, when pulling from the fixed draw bar, pull very slowly.

 

[MossRoad]

 

[the old grind]

As CalG says there is no actual 'climbing a ring gear'. (post #152) The term is folklore and figurative, as if whether the wheels wouldn't spin when a tractor would/did flip over backward by 'climbing'. Still, I wonder about tire slippage 'or not' ...

So looking at these pictures .. is it just me, or ...
Is there a clear view behind any of their the rear tires, or perhaps a visible hint that there could be at least some slippage? (even mere single digit %s)
Are the hookups to sled/load more or less considered to be a) connected below the axle centerline b) of common or 'class' length and .. 20"/20" height/distance?
btw, Can we, or not, see our vector analyses demonstrated here? Are all/any we mentioned clearly illustrated? :scratchchin:

Disclaimer: The following pictures are in the public domain, and shared here without permission.

 

[CalG]

Now if you pull from the top of the ROPS, you're likely to lift the front but it will lift very slowly so it's easy to react to. If you pull from the fix draw bar below the axle you are unlikely to lift the front and even less likely to roll over backwards, but if it does start to happen, it will happen very, very fast. To counter this, when pulling from the fixed draw bar, pull very slowly.

It is important to note that the "rapidity" of the over turn is proportional to the load.

A rather light pull at the ROPs will turn the tractor over rather slowly, while a very STRONG resistive force near the axle location will turn a tractor over backwards quite rapidly. (or restore equilibrium at some :front wheels off the ground attitude)

Back to vectors.. they have both direction, and magnitude!

 

[MHarryE]

Basic physics - even known when I got my engineering degree and available through every states dept of agriculture. Modify your tractor so the coefficient of traction approaches infinity and it’s going to flip backward. The diagram I posted is from a basic tractor engineering book. Pivot point is bottom of rear tires. Multiply force times lever arm to get the opposing moments. Pull times pull height is opposed by mass at CG times lever arm. If the traction is poor the pull cannot reach the point where the front end will lift. If the traction is high the front end will lift, just like shown in all these tractor pull pictures. Same thing in the picture I’m sure everyone has seen of the driver who chained logs to his wheel. Every time a log hit the ground the tractor front raised.