SIMPLE questions about towing 4-Down

[Reacher]

Originally Posted by Mr_D

One thing almost everyone misses is that some states (at least WA, OR and CA) do not consider a motorized vehicle being towed to be a "trailer" and the braking laws change to a performance spec.

https://auto.howstuffworks.com/auto-...gulations1.htm

Now try that on your insurance co after an unfortunate incident.

[bamaboy473]

After 10 pages of education, admonishments, advice and...otherwise...this work in process has reached the beta stage, I think.

Invisibrake was the braking system I bought, and would consider another type if I ever were to install into a sports car with power seats. Jeeps have a lot of room under the driver's seat; not so with BMWs, so the device sits on the rear floorboard, which is not ever going to be a problem for us.

The tow brackets were re-designed in order to provide a correct seating for the Blue Ox arms, and adding chain links for the safety chains was done, too.

Breakaway is inside the engine bay, as is a power wire that will charge the battery while the coach is traveling.

At first test, turn signals and running lights work properly, brake lights don't. That will be the next step, and then the braking testing will start.

Thoughts? What's missing?

[Reacher]

Looks like a well done "professional" job. Congrats and happy towing!

[AKIQPilot]

It appears that your safety chains connect to the same tab coming out of the bumper as your towbar attaches? It lookes like the safety chain even uses the same bolt that the towbar tab uses. It also looks like the entire system is in single sheer.

This is not how a properly engineered flat tow system looks. Its better than your first couple of tries but far from a properly designed and engineered system.

[bamaboy473]

Please explain what "single sheer" means. Google just shows drapes.

Also, from a logic viewpoint, what are the odds that a base tab could be ripped from the frame, or that Grade 8 bolts could snap? It would have to be some un-worldly amount of stress, wouldn't it?

That is what the break-away system is for, anyway, isn't it?

P.S. thanks for the thoughts about how to make it better.

[AKIQPilot]

Originally Posted by bamaboy473

Please explain what "single sheer" means. Google just shows drapes.



Also, from a logic viewpoint, what are the odds that a base tab could be ripped from the frame, or that Grade 8 bolts could snap? It would have to be some un-worldly amount of stress, wouldn't it?



That is what the break-away system is for, anyway, isn't it?



P.S. thanks for the thoughts about how to make it better.

Single shear is when a bolt is used to clamp two pieces of metal together. Double shear would be more like a sandwich where the two pieces of bread sandwich the tab in the middle. The bolt clamps the tab between two pieces of steel spreading the load equally doubling the force required to shear the bolt off.

The hitch point you built where the hitch pin goes through your tabs and the blue ox tab is in the middle is in double shear. All blue ox tow bar fittings are either in double or triple shear. The part of your baseplate where the 1/2” flat bar is bolted to the adapter you built is in single shear.

I will find an example of double shear for you.

As far as the safety cables go, the most likely place for a properly maintained towbar to fail is at the baseplate to towbar connecting points. For this reason most towbars are designed so that the safety cables attach to the frame or to a part of the baseplate that is not part of the towbar connecting point. Essentially the base plate tab could break off and the safety cables are still securely affixed to the vehicles, either directly to the frame or to another point independent of the towbar connecting point.

[AKIQPilot]

Here is an image showing single and double shear. In double shear you have to apply twice the force to shear the bolt as compared to single shear.

[guardrail53]

Originally Posted by bamaboy473

OK, back to the re-design of the towing apparatus. Here is a fabrication to address two of the major concerns; a proper attaching point on the car, and safety chain attachment.
Look at what I'm thinking and give me your thoughts, please.

The safety chains will attach to a horseshoe that hangs below the plate.

I'm thinking of doing away with the Ready brake, and thinking of getting an in-car braking assist.

Is ReadyBrake or similar absolutely critical to have if we have safety chains?

I agree with AKIQPilot, in that it needs to be at least double shear!
Also, looking at your pic's of the prototype, I would gusset the back side also, to help with the force that will be pulling on the straight up piece.
Other than that, looks good!
Let us know how it goes after you tow it! Rail!

PS. I read the whole thread, and waited to comment till the last, just so I would not repeat what others have already said! Some, I would not repeat, no matter what!

[bamaboy473]

Great explanation. The fix would be to remove the bumper skin again and bolster the tab sections. It's also possible that I could add additional tabs that would serve as cable ports for the safety cables. Not exactly a fine-looking set-up, but more in line with a correct way to do it.

Thanks again.