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Rod ends in bending

Posted by Thomas Kimsey 
Thomas Kimsey
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Rod ends in bending
September 19, 2014 08:33AM
Saw this in the latest episode of launch control. Why would Vermont SportsCar risk suspension failure by attaching their knuckle/upright this way. Sure it gives you adjustability but in a Global Rallycross car I would think durability would be preferred. Those threads are never going to be good in shear.




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fiasco
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Re: Rod ends in bending
September 19, 2014 09:43AM
Durability? For a ten minute event?



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Thomas Kimsey
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Re: Rod ends in bending
September 19, 2014 09:45AM
Quote
fiasco
Durability? For a ten minute event?

Have you seen those guys drive? They don't use a steering wheel to turn, they use each other.
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Robert Culbertson
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Re: Rod ends in bending
September 19, 2014 11:30AM
While they are not ideal, if they are big enough you won't have an issue. It's not the best reasoning, but sometimes big and simple wins over lightweight and complicated.

You can also get camber adjustment done very quickly, where with shims it will take a bit longer (unless you're really well prepared with a good design).

Those uprights seem a little crude though , but very simple.
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Thomas Kimsey
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Re: Rod ends in bending
September 19, 2014 12:01PM
Quote
Robert Culbertson
While they are not ideal, if they are big enough you won't have an issue. It's not the best reasoning, but sometimes big and simple wins over lightweight and complicated.

You can also get camber adjustment done very quickly, where with shims it will take a bit longer (unless you're really well prepared with a good design).

I agree that it is easier. Also they look nicer than a fat stack of shims. I just think it is funny that one of the big No-Nos of suspension design ends up on well funded cars. Also shims suck to change if there is safety wire involved.
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Re: Rod ends in bending
September 19, 2014 12:23PM
Thats definitely not the brightest crayon in the box to be using rods ends like that.... but its easy and cheap to fabricate, fix and replace on site. Best option would be to use uniballs but that makes it a more complicated upright design, and will need a strong kingpin.

The only think keeping that wheel from flying off is that toe arm, if that fails for some reason, it will snap the other 2 rod ends so quick that they'll never know what failed first.

But shirley they know betterer
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Re: Rod ends in bending
September 19, 2014 01:29PM
Wait, I'm a bit confused. How is the toe arm different? What am I missing?

Is the thought that the rod ends would rip from the suspension arms? Or is it the little U channels the ends go into, and that bolt being sheared?



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Thomas Kimsey
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Re: Rod ends in bending
September 19, 2014 01:40PM
Quote
Dazed_Driver
Wait, I'm a bit confused. How is the toe arm different? What am I missing?

Is the thought that the rod ends would rip from the suspension arms? Or is it the little U channels the ends go into, and that bolt being sheared?

The issues with rod ends in bending is the threads. Threaded material is good in taking forces in tension and compression but not really in bending. What happens is the threaded part bends and deforms. It may even bend and then you get shearing loads at the threads and the result is the rod end breaking off at the threads. You can also have distortion in the spherical and cause that to seize. In road race cars the main cause of rod end failure is braking since the super sticky tires facilitate massive grip and massive load. In rally applications you have the grip and the track roughness to worry about.
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Robert Culbertson
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Re: Rod ends in bending
September 19, 2014 03:44PM
The toe link is a much smaller rod end, and is usually the first thing to break when there is an impact. When the toe link breaks the wheel usually slams into the control arm, which either bends/breaks or breaks the upper and lower rod-end mounts.

I also like how the rod end is taking all the drive and braking forces (probably much higher than suspension loads) in the weakest direction.
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Re: Rod ends in bending
September 19, 2014 04:12PM
Is it just the pic or does it look like they put some angle on the rod end to compensate?
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Re: Rod ends in bending
September 19, 2014 05:02PM
looks like the front end of a late model dirt car, in away.

they never get to far from the service crew, so it most work for them



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Re: Rod ends in bending
September 19, 2014 08:17PM
Quote
Thomas Kimsey
Quote
Dazed_Driver
Wait, I'm a bit confused. How is the toe arm different? What am I missing?

Is the thought that the rod ends would rip from the suspension arms? Or is it the little U channels the ends go into, and that bolt being sheared?

The issues with rod ends in bending is the threads. Threaded material is good in taking forces in tension and compression but not really in bending. What happens is the threaded part bends and deforms. It may even bend and then you get shearing loads at the threads and the result is the rod end breaking off at the threads. You can also have distortion in the spherical and cause that to seize. In road race cars the main cause of rod end failure is braking since the super sticky tires facilitate massive grip and massive load. In rally applications you have the grip and the track roughness to worry about.

So, as they're mounted vertically, how is this different than rod ends suspending a live axle? Or am I still missing something? I see metal on both sides of the rod end, so the bolt is supported the same, and it's moving in it's larger range of motion orientation.

Does this just have more force than the live axle would transfer? confused smiley



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Re: Rod ends in bending
September 19, 2014 08:20PM
Quote
Robert Culbertson
The toe link is a much smaller rod end, and is usually the first thing to break when there is an impact. When the toe link breaks the wheel usually slams into the control arm, which either bends/breaks or breaks the upper and lower rod-end mounts.

I also like how the rod end is taking all the drive and braking forces (probably much higher than suspension loads) in the weakest direction.

Ah, so is this problem design related, or execution related? Could they have made the mounts beefier and solved the problems?

Your last bit there, do you mean that instead of the rod being able to move freely (as its in line for travel) the forces are going through it through it's smaller range of motion?

Does that question make sense?



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Re: Rod ends in bending
September 19, 2014 10:31PM
I suppose the $64,000 question is, are they failing in service or does it meet strength/durability criteria?



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Re: Rod ends in bending
September 19, 2014 11:07PM
It looks fairly straight forward and obviously easy to service. It works for them!

Hope to catch a glimpse at Dirtfish soonsmiling smiley)
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