Quote:
Originally Posted by andrewwynn
Option two: These are 16' 2x6. They were wet and super heavy. My crossbars are only 3/4" tall not designed to hold much load but with only 16' I can shift toward the back and support up from my tail rack. |
As shown in the photo there, the support from your tail rack is adding stability (and is surely helping a lot in that regard), but cannot be taking much load at all off the roof racks.
To understand why, without drawing a free body diagram, imagine if you yourself were holding those beams with your hands, in the middle of course. Then your 7-year-old tank commander went and tried to help by lifting at the very end of the beam. They could very easily move that end up and down, without taking hardly any of the load. You'd still be carrying the same weight.
With the beams strapped securely to the two cross bars, it may be possible to exert some force on the end. But that will not be taking any of the net load off the bars, the force will be counteracted by the torque between the two bars. The net force on the bars remains the same, with the extra torque superimposed - so it's actually worse in terms of having a peak force causing structural failure.
The added stability and reduction in bouncing will definitely be helpful though.