Spring bar selection

Ron Gratz wrote:

JBarca wrote:

The lighter bar will try and deliver all it can and the loaded TW has the ability to be 2 times the weight pushing down on the ball then the WD bar may have been tested for. Will the WD bar permanently deform? This goes directly against the Reese warranty.

Since the "back flex" induced added deflection will be essentially the same, the lighter and more flexible bar will experience less added load than will the heavier bar.

If one uses a 1,200# WD bar on a 1,200# TW and adjusts the WD hitch to only deliver the force needed for 50% FALR, then the back flex situation should not affect the WD bar as it has been fully tested to comply with this situation. Or has at least been proven by consumers to not bend in most cases.

I think it also is safe to say that a 1200# bar on a 1200# TW at 100% FALR has been proven by consumers to not bend in most cases.
A 1200# bar generating 100% FALR with 1200# TW will be loaded to about 960#.
A 600# bar generating 50% FALR with 1200# TW will be loaded to about 480#.
If "back flex" results in a doubling of the load on both bars, each bar will end up at 160% of its assumed static working load limit.
The load on a bar is not determined by TW -- it is determined by how much load it is asked to transfer.

Ron

Hi Ron,

Thanks for the response and detail. Sorry this took so long to respond back, life has been, busy.

I agree with your response for the most part however there is still in my mind dynamic situations that have me concerned using a heavy TW with a much lighter WD bar as a recommended setup.

When the road the TV is riding on is on an angle to the TT, the TV turns, while going up hill, that motion tilts the hitch head in 2 directions. The tilt and turn can unload a large percentage of one of the WD bar leaving the other WD bar heavily loaded. The DC users have this even worse then non DC users.

With the hitch head titled both back from the "back flex", one bar carrying the majority of the load as the head tilt created this, in this condition the TW provides the downward push on the ball to generate the tension that the WD bar is now positioned at. The bar is being asked to provide more force exertion. In this condition, the heavier TW will result in more bar flex then a lighter TW. Did I mix this up? The combination is asking the WD bar to deliver more force and thus more flex.

Granted these turns do not happen all the time, but they do happen. We never yet solved the heavy snap up failure of when the DC is added to a hitch so this force does exist on one WD bar as proven by several ORF members.

If we knew the working displacement limits of these spring bars before we approach the yield point, then I could agree using a 600# WD on a 1,200# TW and only shoot for 50% FALR providing the rest of the hitch can handle it. As long as the flexure of the WD bar does not exceed the working limit, it can flex many times to this limit and not deform. One too many times over that limit and it will stay bent.

The new guidelines for FALR have not yet caught up to how to rate the WD bar. 600# bar on a 800# TW, I'm not that concerned. 600# on a 1,200# or worse 800# bar on a 1,700# TW, I'm concerned. Maybe it is me and having seen too many fatigued out springs in machinery work that once the design allows the spring to go past the working limits, it breaks prematurely. Many spring failures come from exceeding the working limits with high duty cycles.

I agree we may not get the hitch mfg's to help sort this out for us for many years to come. And yes, I'm glad to see the shift from "equal squat" finally in print and especially from Progress Mfg. And in their case, would they warrant a 600# WD hitch system with 600# WD bars on a 1,200# TW? Good question. They make different heads per spring bar ratings. Until they test it and prove it, I would say no. Reese and others use the same higher rated hitch head and just change WD bars so the head and shank could be up to the task assuming the WD bar can take it.

Thanks

John