AL rear bumper support with Hitch... ?

[ZainRacer]

I wanted to add a trailer Hitch to my S13 so I could use a hitch style bike rack; I tried the trunk mounted ones but they didn't work too well. I might also use it for a track trailer sometime down the road. Just wanted to get some input before I order the materials.

This is the hitch I am planing on use.

Reese Towpower Step Bumper Receiver 81378


here is a model of what I am thinking about doing...


- 3" Aluminum Channel (1/4" thick) for the main support/beam.
- 6" Aluminum angle (3/8" thick) for the hitch mount.
- 1.5" x 1.5" Aluminum Channel for the Bumper support mounts/rails.

It should weight around 26lbs total, the Hitch weights ~10lbs.
Total Cost should be ~$140 which is close to how much a Curt Hitch costs.

Should I add more supports or braces anywhere? Is there anything else that I should change about it?

[Matt93SE]

1. Aluminum is not great for this kinda stuff.
2. That chunk of angle that holds the receiver onto the bumper will be a SERIOUS weak point.
3. C-channel with a twisting moment won't be that great either.

I'd recommend going to square/rectangle tube on the bumper itself, and adding some support along the sides of the angle if you still have to use the angle like that.

If you use the c-channel, I'd also add a small backing plate around the bolt holes to spread the load over a bit more area so it doesn't fatigue around the bolt holes and tear apart.

[Def]

6061 is right up there with the steel the unibody is made from wrt ultimate tensile strength. Yield its provably a bit down, but the real problem is its way down in fatigue str.

The bending moment is your biggest problem. Does the hitch need to be that low? That's only a few inches above the ground in my car.

If you eliminate the bending moment I think it'd hold for at least a while.

[ZainRacer]

Thanks for the feedback!

At the location I have it right now, the license plate will sit directly above the hitch. There will approximately 6" between the bottom of the hitch and the road; it will be a little less with the rack and bike weighting the car down. (~75lbs).

I could move the hitch about 6" higher so the hitch sits directly above the license plate. This would put the hitch at a better height and if I am thinking about it correctly it should reduce the bending moment. If I moved it up I would have to cut an opening in my bumper for the hitch, and the hitch pin would be harder to reach.




or I could move the hitch up a few inches from the original location and move the license plate up and bolt it to the outside of the bumper cover.


like this (same as the model above just flipped upside down)



Another option would be to weld something (square tubing?) on to the hitch that extends back under the car and brace that to the bottom of the trunk similar to how the curt his is set up.

Curt Hitch for S13



If I can figure out how to set it up properly, I am going to run some stress analysis to get a better idea of how everything would react under load. I am fairly new to CAD and haven't taken any CAD or Design classes yet so I am not very good with it, but the Tutorials have been very helpful so far!

[cozzmo]

Of little help i'm sure but my B14/N15 has got a piece that goes under the spare wheel well and an insert that replaces one of the drain plugs as a brace for the factory nissan tow bar that i have.

[djsilver]

I bought a Curt hitch (De'lan is the same) for my S13 and it was pretty worthless. I cut the flat bar off and welded a 1-1/4" receiver on but it couldn't handle any weight to speak of. I spent some time looking under the back of the car and figured it would take quite a bit of steel to make it better and eventually gave up on the idea completely. It travels to events on a trailer now.....,