tubular lower control arms for coilovers

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well thats just great,someone managed to run off the second decent fabricator this site had.

i'm always open for new ideas to do my own fabricating.
 
THAT SUCKS!! I'm sorry to hear that Junior. I really liked your design and your skills. Best of wishes.
 
HDK is selling LCAs for the coil over conversion. They are similar but so are Bobsprofab's.

My Demon already has tubular UCAs and I need to change to coil-over for more room for headers, so torsion bars have to go. So I am one of the gunny pigs on the HDK upper shock mounts and the LCA kit.

On the set shown here I see no reason for supporting the rear of the pivot as there is hardly any cantilever. Hell, I can't see needing it on the HDK arm and it has a lot more cantilever because it has two bushings like a motorcycle swing arm. The stock UCA pivot is also cantilevered. My KOS Demon has the stock LCAs and has done a lot of huge wheelies. We'll see how the pivot mounts on the K frame held up when I pull it but the car drove straight. That area will be reinforced.

My bet is the pivot does NOT need reinforcing.
 
airwoofer said:
HDK is selling LCAs for the coil over conversion. They are similar but so are Bobsprofab's.

My Demon already has tubular UCAs and I need to change to coil-over for more room for headers, so torsion bars have to go. So I am one of the gunny pigs on the HDK upper shock mounts and the LCA kit.

On the set shown here I see no reason for supporting the rear of the pivot as there is hardly any cantilever. Hell, I can't see needing it on the HDK arm and it has a lot more cantilever because it has two bushings like a motorcycle swing arm. The stock UCA pivot is also cantilevered. My KOS Demon has the stock LCAs and has done a lot of huge wheelies. We'll see how the pivot mounts on the K frame held up when I pull it but the car drove straight. That area will be reinforced.

My bet is the pivot does NOT need reinforcing.
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Interesting thoughts... I'd be curious to see how much load actually gets passed to a single shear stock LCA mount pin.
 
I just started reading this thread....very interesting and very good fabrication, as I have been thinking about modified A body front suspension work. I almost hate to bring this up, but I can't look at this and not do some analysis on something that jumped right out as a possible issue. (I sincerely apologize to the OP for saying this after so much hard work.)

The issue raised earlier in the thread about the stress in the threaded portion of the rod end sticking out of the end of the LCA is very real. Some straightforward calculations, with a typical car weight just sitting still and assuming 3/4" fine threads on the rod end, shows the stress on the lower edge of the threads where it enters the threaded bushing to be around 50,000 psi. Yield strength of 4130 steel is in the range of 66,000 psi.

So it looks like it will not take much impact loading (think: small pothole) to bend the threaded portion of the rod end. And yeah, I realize not all calculations are the end-all and be-all, but this is so close (in just a static setting) to the yield strength of a strong steel that it looks to have very little margin. And the earlier info about the rod end strength of 15000 is likely for radial strength; that has no bearing on how this part is being applied.

Bottom line: Rod end are not designed to be used with cantilevered loads on the threads, which is inherent in the design here. I see the inner pivots of some wishbone LCA's using rod ends in a similar way, but the mitigating factors in those are that these use 2 rods end to split the load, and the force acting on them is a fraction of the load in this type of set-up.

You can read here to see more on this and duplicate the computations:
[ame]http://www.aurorabearing.com/pdf/rod-ends.pdf[/ame]
and here:
[ame]http://americansolarchallenge.org/ASC/wp-content/uploads/2013/01/rod_end_calculations.pdf[/ame]

For reference on another aftermarket LCA design, look at the HDK tubular LCA's and see how the material between the ball joint mount and the end of the tube and coil-over is short and stout. The short distance lowers the bending moment considerably, and that, plus the increase in thickness, makes the internal stress around 20-30 times lower than in the design shown in this thread.
 
Jump over to the HDK tubular coil over for stock steering thread. He has a dual poly bushing deal and I am testing a set. I plan to cantilever it from the K frame and not have any brace on the end, just a washer to retain the bushing/arm. I working with HDK now on a mod to the K frame to hopefully allow this.

The stock deal was OK and needed for a class back in the day (I think), but now I need header room and the bars have to go.

If you are any good at structural analysis hit me with a PM.
 
BTW for all, I did not realize when I posted above that I could be stepping into the middle of a 'design stealing' controversy. I had honestly not read any of the threads here on the LCA's designs floating around; I have done such tubular LCA designs a few years in the past for another car, and am starting to look into this for the Mopar A's. I just started with this thread and saw what I thought was weak, made a quick, simple analysis, and thought it was worth sharing.

The comparison to the HDK item was made only because that is a well known company here and I thought it would be a comfortable basis for everyone to compare..... never having read the the other LCA discussion that Airwoofer referenced above and seeing the controversy.

So, did I ever step into it! I hope everyone will accept that I am not taking any sides here, just trying to analyze and share. Tubular control arm designs have existed for decades, so it never occurred to me that anyone would even entertain the idea of design stealing....
 
nm9stheham said:
BTW for all, I did not realize when I posted above that I could be stepping into the middle of a 'design stealing' controversy. I had honestly not read any of the threads here on the LCA's designs floating around; I have done such tubular LCA designs a few years in the past for another car, and am starting to look into this for the Mopar A's. I just started with this thread and saw what I thought was weak, made a quick, simple analysis, and thought it was worth sharing.

The comparison to the HDK item was made only because that is a well known company here and I thought it would be a comfortable basis for everyone to compare..... never having read the the other LCA discussion that Airwoofer referenced above and seeing the controversy.

So, did I ever step into it! I hope everyone will accept that I am not taking any sides here, just trying to analyze and share. Tubular control arm designs have existed for decades, so it never occurred to me that anyone would even entertain the idea of design stealing....
Click to expand...

No big deal on bringing it back up. I'm over it.

For anyone that isn't, I'm not going to sit here and argue about it all again either....

I understand that it could be weaker. The whole reason i even started down this road was because i needed to bring the wheels in. In order to do that i needed to know how far in i could bring the upper as well as the lower before the upper hit the coil over. Seemed easier to me to just make at least the initial set adjustable. In my case the rod end is screwed in as far as it will go which helps. I also don't believe that the rod end alone is taking the sole force of all the energy, a lot of that has to be being transferred through the other contact points etc. I never really showed these as finished with bump stops or the final strut bars and mounts or any of the other things i had planned to add or offer.
 
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