extending hitch; anyone see an issue with my math?

[steiny93]

Currently the 5th wheel hitch (Air Safe) is mounted on top of a pair of 4" x 6" rectangular tubes 1/2" walled 17" long sitting on the tall side (6").

The hitch and those tubes are bolted through a 1/2" plate which is attached to the top of the frame rails.

Four bolts are holding the hitch to the 1/2" plate through the 4x6 tubes which are 5/8" grade 5 bolts

 

[i apologize for no pics]

 

I need more clearance between the 5th wheel and the atv's I'm putting on the bed of the HDT, 28" would be perfect.

If I take the 17" long 4x6 tubes and re-do them at 45" long.

Doing so would have the first 20" fully supported by the 1/2" plate then the remaining 25" would be in overhang beyond the plate.

 

Those tubes would then be held on by four 5/8" grade 8 bolts; combined providing 588k lbs of proof load (grade 8 is 120k psi)

The tubes at 6"x4" by 1/2" walled in the length of 45" with 20" supported has a max bending movement of 32k lbs combined (both tubes, 30k psi steel and .55 yield).

 

The trailer we would be pulling in this config is light

2500lbs pin

16.5k gross

 

Does anything about this plan seem off to anyone?