experienced myself a rod end failure during a race on the Spoon upper conrol arm (rear)

 

Any updates on the arms.. would love to see pricing and availability..

david

 

The bending comes from the strange extended wishbone geometry. The inside points are effectively pure tension/compression. It would be really be smart to consult someone who understands structures before designing more car parts.

 

I think you guys need to reread my post. The failures you have seen are from suspension travel issues. On the upper arm, there shouldnt be any bending load on the outside mounting point unless the joint itself goes into bind. Which is a bad design. Sorry you wasted your money on parts that didnt work but you dont need to take it out on me.

 

Where does the torque from braking go? I agree that in pure cornering there would be no/minimal bending on the outer rod end. I'm not "taking it out on you", I'm trying to help avoid an expensive/dangerous failure. Take it as you wish.

Do a free body diagram of both the hub and each arm under braking before completely dismissing this warning. Or just look at any formula car to see how many rod ends are on the outer end of a control arm.

 

We are not going to go anywhere. The bending your talking about is still going to exist on the inner mounting points. Yes I worked on formula cars, no not FSAE.

What we are basicly talking about is the sheer strength of the outter mounting point. Simple fact is that my arms have 3/4" threaded joints. Show me the failed arms and look at thier joints and compare the size and sheer strengths.

Yeah, you get more load on the outside joint then the inside because the load is spread over 2 joints but that doesnt mean that load doesnt exist. Like I've stated, it is alot easier for people to mess up thier suspension geometry by making something adjustable that really shouldnt be adjusted. Trust me, its alot easier to use rod ends for the inner pick up points then the sephericals, but using the sephericals are better in that they are much stronger, last longer, and would never come loose or be adjusted wrongly.

Seems like when we are talking about "bending" we are getting confused as to what type or what axis of load it is. On my last post "bending" meant a vertical load on the arm itself. Braking load isnt as great as a bind.

 

 

 

There is only one kind of bending.

Here is what wikipedia has to say about it.

http://en.wikipedia.org/wiki/Bending

A spherical bearing or rod end are not capable of reacting moments, only directional forces. Therefore, there are only two lines of action which are internally possible within an a-arm, one from the outboard joint to the forward joint, and one from the outboard joint to the aft joint.

When there is no longer a direct section of material between the two, the stress has to flow around. Enter bending.

 

O well, have fun with all your broken parts guys.