Expedition vs. Durango?
I have a 27' TT, 5200# dry, estimated 6,000# loaded, 650# tongue weight empty. Have a Reese WDH. Plan on going across the Rockies. Bought a 2008 Expedition with 9,000# tow capacity, duh, doesn't fit i...
Forum Discussion
While concerns regarding concentrated loads on a unibody is valid, I think this is one area where we should put out faith in OEM engineers. I doubt they'd release a hitch rating without considering all static and dynamic forces acting on the hitch.
We can do some very simple calculations. Assuming worst case of 1000 lbs hitch weight with no equalizing hitch. Then assume a drawbar length of 1 foot, and a hitch mounting hole spacing of 1 foot (2 bolts per side on the Durango).
Simple free body diagram would tell you the rear bolts have a net force of 2000 lbs down, and the front bolts 1000 lbs up.
2000 lbs split into 2 bolts means 1000 lbs per bolt. A typical automotive frame/subframe should be at least 40ksi in yield strength. Meaning each frame rail only needs to be 0.025 square inches in total cross sectional area to support the weight.
I can guarantee the most flimsy frame in the world should be 10 times that amount!
We can do some very simple calculations. Assuming worst case of 1000 lbs hitch weight with no equalizing hitch. Then assume a drawbar length of 1 foot, and a hitch mounting hole spacing of 1 foot (2 bolts per side on the Durango).
Simple free body diagram would tell you the rear bolts have a net force of 2000 lbs down, and the front bolts 1000 lbs up.
2000 lbs split into 2 bolts means 1000 lbs per bolt. A typical automotive frame/subframe should be at least 40ksi in yield strength. Meaning each frame rail only needs to be 0.025 square inches in total cross sectional area to support the weight.
I can guarantee the most flimsy frame in the world should be 10 times that amount!
