Yeah, I've read that thread on the Commy forum, and have a few opinions on it.
Firstly, I doubt whether you will break a "healthy" tow ball with a smooth pull.
The vehicle should lose traction long before enough forces to break a tow ball, even with the best tyres.
An emergency stop, with a large trailer/caravan will most probably create larger forces.
Once you start "jerking" though, it turns into a "snatch" and anything can happen!
On snatching, and breaking tow balls / bars:
- The forces involved in snatching and those involved when towing/pulling, are not of the same order of magnitude.
Because I prefer to err on the safe side, I would never recommend doing a snatch using a tow bar or a tow ball.
I doubt however whether the forced involved in a "proper" snatch are large enough to break a "healthy" tow ball.
The question then is what a "proper" snatch is.
- I have watched many snatching videos on the web, and am convinced that most of the "experts" don't understand the physics involved fully.
I am convinced that most snatches (and certainly most of those where breakages occur) happen when the kinetic limits of the snatch rope are exceeded.
The specification for kinetic ropes usually states that snatch should be done in such a way that it is ensured that the length of the rope should never 110% of it's unstrained length (when new).
In most snatches this is ignored. The snatch is done in such a way that the kinetic rope exceeds it's kinetic limits, and it then becomes just another "solid" rope.
When this condition is reached, the recovering vehicle is still moving, and the forces exerted on the rope (and thus all attachments and connectors) FAR exceeds the design parameters of the kinetic rope.
To give an analogy of what happens, imagine this:
You have to "cushion" the weight of a falling mass.
To do this, you place a coil spring in an upright position underneath the falling mass.
As the mass falls, it compresses the coil spring.
NB. Ideally it should stop the falling mass
before it is fully compressed.
The momentum of the falling mass is "damped" because of the kinetic properties of the coil spring.
The forces transmitted to the ground through the coil spring are thus also "damped" (the force is applied over a length of time, and not as one impact).
Imagine however, that the coil spring is to "soft", and cannot support the falling mass!
The coil compresses fully before the mass is stopped.
The damping effect still occurs, but the mass is still falling when the coil is fully compressed.
The coil spring now acts the same as a solid piece of steel, and the momentum of the mass is transferred to the ground without any further damping effect.
You can now realistically expect damage to all the components involved: mass, coil and the earth!
Summary:
I doubt whether a "smooth" pull will break a tow bar/ball.
