Rodan
Rodan Dork
2/26/20 9:55 a.m.

I am planning to tow our Bronco:

behind our Camper:

for the purpose of back country exploring where a trailer is impractical for the campgrounds we'd be staying at.  I have researched and understand the pros/cons of flat towing, but it's looking like the best option for our goals.

After looking at commercially available tow bars, I have decided to build one instead of buying.  The front will be a normal trailer connector to attach to the truck's hitch.  When I fabricated the bumpers for the Bronco I built in 3/4" recovery points that are welded through the bumper to the mounting structure directly in-line with the frame rails.  I have no doubts about them being strong enough for an attachment point.  I have already obtained adapters to attach the tow bar to the recovery points:

I have three main questions regarding the design of the tow bar:

1.  Materials:  I was planning to use 1 3/4" DOM tubing.  Simple 'A' frame design.  Thoughts?

2.  Length:  My reading has indicated longer is better, within reason...  I was thinking 4-6ft.  Thoughts? (The bar will not remain attached to the Bronco when not towing).

3.  Tow bar angle...  this is the big one.

In image 'A' above, the tow bar is at a 'down' angle from tow to towed.  My research indicates this is less desireable because it puts an upward force into the tow vehicle under braking which can contribute to instability.

Image 'B' shows the tow bar in an upward angle from tow to towed.  Theoretically, this would contribute to stability under braking by adding a downward force on the tow vehicle.

I realize that dead level is best, but the Bronco tow points are at 31" off the ground (truck is ~24" with no rise), so I'm leaning toward 'B' planning to keep the overall relative rise from tow to towed under 6" using a hitch with the appropriate rise.

Thoughts?  Ideas?

Robbie
Robbie MegaDork
2/26/20 10:25 a.m.

I think you've pretty well nailed it. I use the HF tow bar and it is built with c channel, I can grab measurements if you want me to. For material strength comparisons, and overall length.

Remember to unlock the steering and put the tcase in neutral.

The largest forces on the tow bar come when turning in tight circles, and changing direction (going from tight right turn to tight left). 

Robbie
Robbie MegaDork
2/26/20 10:26 a.m.

Zip tie a brick to the brake pedal in the bronco for surge trailer brakes, redneck style?

Cactus
Cactus Reader
2/26/20 10:37 a.m.

In reply to Robbie :

Lol. Might need a 12v vacuum pump applied to the booster to help with that, but I like it.

Rodan
Rodan Dork
2/26/20 10:52 a.m.
Robbie said:

Zip tie a brick to the brake pedal in the bronco for surge trailer brakes, redneck style?

Yeah... no. cheeky

Definitely going to use a commercial remote braking system of some sort.  

Curtis73
Curtis73 MegaDork
2/26/20 11:46 a.m.

You've nailed it pretty much.  Keep the angles low, and don't underestimate the side-to-side loads when you build the bar.  A good solid cross bar just in front of the bronco's bumper is wise.  Your recovery tabs are super beefy in the front-rear way, and likely more than adequate side to side.  A cross bar adds strength in a collision.  I have seen towed unibody cars that just split the front in half during a panic stop or collision because they were using a universal tow bar that didn't link the two sides of the A-frame. 

Is the bronco a solid front axle? Twin I-beam? IFS?  Either way, consider altering caster and be prepared to change toe a bit if you encounter pulling side to side.  Many modern cars with lots of caster don't tow well.  They "dart" back and forth.  They'll slowly go to the right within the tolerance of the pins on the tow bar, then yank back toward the left.  It's very subtle, but it causes constant correction from where you sit.  YMMV.

Rodan
Rodan Dork
2/26/20 12:38 p.m.

In reply to Curtis73 :

It's got the stock TTB axle, with a 4" lift.  It got new urethane axle pivot and radius arm bushings, and all new steering links/ball joints a few months ago.  After the parts were installed, I had it aligned.  Current numbers are .06" (1/16") total toe and ~4.5* caster.

 

oldopelguy
oldopelguy UberDork
2/26/20 12:58 p.m.

Since flat towing has essentially zero tongue weight on the tow vehicle you can finesse the draw bar more than what would be recommended for a trailer; I'd get that coupler as high as you can to get the bars level,  even if you have to fabricate a new draw bar.

Every tiny bit of slop is going to magnify with a tow bar. If you can take the adapters you got and shake them side to side more than 1/8" or so I wouldn't use them.  I prefer a bar that is a triangle, and top plates on the rear corners tie into vertical tabs for each side of your recovery tabs easily and strongly.

I prefer longer vs shorter, and with your existing height difference I would definitely error towards the long side. That angle is going to try to shove the back of the tow vehicle down and pole vault the front of the Bronco under heavy braking, which may not matter a lot but can sometimes toss a wiggle into either of both vehicles. 

And you're not going to like it, but if you plan on highway miles under tow you're going to want to consider getting a set of smaller, thinner, shorter sidewall, highway tires to put on the Bronco on the highway.  Off road tires usually get chewed up quickly by tow bar towing, like 5k miles quickly, and the better tje tires are off road the worse it is going to be.   Good news is that will help with the tow bar issue, bad news is carrying around the off road tires. 

Curtis73
Curtis73 MegaDork
2/26/20 4:10 p.m.
Rodan said:

In reply to Curtis73 :

It's got the stock TTB axle, with a 4" lift.  It got new urethane axle pivot and radius arm bushings, and all new steering links/ball joints a few months ago.  After the parts were installed, I had it aligned.  Current numbers are .06" (1/16") total toe and ~4.5* caster.

 

Looks good.  If you notice some left-right, you can probably just deal with it.  You have enough tow rig that it shouldn't be too bad.

Rodan
Rodan Dork
2/26/20 10:20 p.m.

Thanks for the input, guys.  I realize flat towing is not ideal, but it serves a purpose.

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