Pull from the front or the rear?

[AndyMA]

Correct if your pulling the trailer uphill when the brakes lock. No net downward force on level ground An upward force if the breaks lock while pulling downhill

Andy

 

[California]

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

 

[AndyMA]

How do you figure that? The load shifting to behind the axle on a single axle trailer will cause an upward force at the drawbar.

Try googling force vector force vector - Google Search

The only reason I keep pushing on this concept is that your misunderstanding of how forces are applied could get you or others hurt

Andy

 

[California]

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.

 

[CalG]

Haven't you seen the nose of a car drop when the brakes are applied? 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.

 

[California]

I'm trying to imagine your scenario: tractor pulling a trailer uphill and suddenly the trailer brakes lock.

That's going to shift the trailer's CG to the rear suddenly? How?

 

[Jstpssng]

I think not as easily broken as a chain. I like to lay a horse blanket across the cable when pulling. I've never broke a chain myself but have heard that not the best to pull with.

A lot of it depends on the strength of the tow strap or chain. One trick that I have seen was two chains, one attached to each vehicle with the other end of each attached to a tire (no rim). That enables you to "snap" it a little bit with the tire absorbing some of the shock.

As somebody has mentioned though, there are times when it's safer to call a wrecker. They can pull more gently, and hopefully their rig is heavy enough to control the stuck vehicle when things start going sideways.

 

[the old grind]

There are a fair number of dead tractor drivers that would dispute your theoretical wandering if they could.

In support of this truth that challenges mere vector analysis: Spinning tires lose some traction, but not all traction. Ever seen a one on one pull, where the 'loser' slows but doesn't stop the winner? When touting vector analysis we might quickly assume that tires either spin or grab. They CAN do both!

Those dead operators that Rick mentioned did not assume as so many of us have that the tractor couldn't be going backward slightly with nothing broken and while still having enough traction to 'climb a ring gear' (I'd heard the term 35 years ago among employers when I was grooming harness horses.)

One of them had died when pulling a hay wagon on level ground from the true drawbar below the axle. Tires spun, the tractor shifted back mere inches, and IIRC he was pinned between the the steering wheel and the trailer tongue. Wheelie bars on a pulling tractor?? You darn betcha, and if you ask the guy who has them, be prepared to hear at least one story you likely won't believe.

 

[California]

'climb a ring gear'. Yes. That's the description that most clearly distills how this can happen. In the real world.

 

[CalG]

climbing ring gears only happens in the world of inertia, Not tractive forces.

If the draw bar is below the axle, pulling on the load forces the front end down.

If the load goes slack, and the tractor is allreading headed for the moon, Well, You can't fix stupid!