Savvy off-road sold? (the unofficial Savvy customer support and Savvy rant thread)
- Thread starter Gollywomper
- Start date
Hey, Sri - are you familiar with Clifford Stoll? His book, The Cuckoo's Egg, was a fascinating read detailing his persistence and obsessive attention-to-detail, and how it lead to the arrest of a hacker back in the 80s. I read it a long time ago...
And if anyone's wondering - yes, I'm purposely derailing one of the most interesting threads on this forum! I wanna see how many pages we can get it to! 
And I have read that book. Excellent read and excellent story!It might be prudent to expand this discussion.
One element of the Savvy bumper that I lack understanding of is the reinforcement bend at the back of the winch deck. Why does it matter, and why was the original designed this way?
Here is my understanding. Bending sheet metal increases it's stiffness, a process called strain hardening.
The goal then is to create a bend that reaches ultimate tensile strength just before necking/fracturing starts to occur. I would assume that the 90 degree bend seen on the original Savvy is right at this point (which I believe is the minimum bend radius for 3/16" 6061 T6).
The remaining question then is how big does the "bent up" area need to be? Does more = betterer?
To keep it the size that is is, means there might've been evidence of damage (from sustained winch pulls I assume) at smaller bends, but not at larger ones.
The simple answer is that bend is a gusset to help stop the deck from bending during a winch pull. The double layering from the fairlead mount was done to prevent the same problem.
The new bumper is made of 1/4" 6061 T6 (as opposed to the original 3/16"). This bumps the minimum bend radius from 0.5625" to 0.875".
If the above information is true, this might just be the largest bend they could get with the thicker material.
My uneducated guess is that it is not as effective as the 90 degree bend seen in the original Savvy bumper. The increased height might then be an attempt to get back some of that tensile strength.
If you are bending a flange to increase the stiffness of a flat sheet, you can think of it in two extremes, a perfect 90 being one, unbent and flat being the other. The closer you get to 90, the more stiffness there is to be had which equates to resistance to bending. The further from 90 you get, the less resistance to bending there is to be had. However, a good engineer can point out the effectiveness of a 45 which I don't believe would be half as good as a 90 but somewhat less. I could easily be mistaken.
The main reason for keeping an eye on deck rigidity is the deck forms the other side of the box the winch is built from. The tie bars, cross brace at the top of the drum form one side of the box, the deck forms the rest of it. If the deck flexes, that will break the winch feet off.
There must be an engineer or two on here that could calculate the strength difference between a 90 degree bend in 3/16", and the new angle in 1/4".
As well as finding out what surface area the flange on the new bumper is needed to make up that strength difference.
Good point. This is a "clear miss" on the new bumper.
Old winch deck having 2 layers of 3/16" vs. new having 1 layer of 1/4" that has lost some of it's heat treatment. I imagine it's a substantial downgrade.
Seems like the guys that enjoy doing calculations are @sab @gasiorv and @freedom_in_4low see if any of them want to do it.
gasiorv
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#2156 and Savvy in the title, No way I am reading anything above this to see what you all are talking about in this post. Not sucking me in.
It's about this post, very engineering oriented and would be good for the discussion.
https://wranglertjforum.com/threads...port-and-savvy-rant-thread.68187/post-1620824
Here is a neat basic article of the concept.
https://sendcutsend.com/blog/the-science-behind-bending-stiffness/
It is mostly to deal with the area moment of inertia. Think of a 2x6 laid flat vs upright for something like a floor joist.
https://sendcutsend.com/blog/the-science-behind-bending-stiffness/
It is mostly to deal with the area moment of inertia. Think of a 2x6 laid flat vs upright for something like a floor joist.