Tip up and flip-over backpack class III hitch rack

[andrewwynn]

@srmmmm: that makes model was inspiration for my design but won't work upside down and I get a bonus tow ball in addition to less wobble. It's a decent value for a canned flip up.

@X53: oem receiver. Also you used "quote" vs reply so my entire first post is duplicated.

@JCL total weight about 120# for the tool boxes. Original rating of 500# on the carrier but I would derate to 400# just in an abundance of caution. 1/2 inch bolts grade 5 have 10,200 # sheer strength through the threads and there are two of them. I didn't measure the torque moment yet but pretty confident the bracket would fail before the bolt and its hefty 1/4 inch. Even basic steel is 40ksi means 10,000# force to start to deform.

Fortunately I'll likely never load more than 200# but will be doing some measurements to determine the force multiple on the steel pin and the bolts.



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[JCL]

Originally Posted by andrewwynn

@JCL total weight about 120# for the tool boxes. Original rating of 500# on the carrier but I would derate to 400# just in an abundance of caution. 1/2 inch bolts grade 5 have 10,200 # sheer strength through the threads and there are two of them. I didn't measure the torque moment yet but pretty confident the bracket would fail before the bolt and its hefty 1/4 inch. Even basic steel is 40ksi means 10,000# force to start to deform.

Fortunately I'll likely never load more than 200# but will be doing some measurements to determine the force multiple on the steel pin and the bolts.

While the carrier may have a rating of 500 lbs, the OE receiver has a rating of 600 lbs applied at a maximum horizontal distance of 8" from the pin. Estimating 24" for the CoG from the pin with the carrier, the rating would therefore be 200 lbs at 24", just due to the moment arm. That includes the both the carrier and the tool boxes. It does not consider any additional derate for a bouncing load.

Edit: Out of interest, I looked up the maximum tongue weight that BMW publishes for the OE E53 receiver for off road use. It is 330 lbs at 8" from the hitch pin. In my mind, the reduced rating is most likely due the effects of a bouncing load, not commonly seen with a ball mount trailer due to the inertia of the trailer. One can decide if that rating is appropriate or not, but it does illustrate that BMW have calculated what the receiver is designed for (considering the mount to the vehicle, not the receiver itself, IMO).


Jeff