Independent Rear Suspension, OEM, aftermarket, stock configuration or heavily modified, all makes and models, everyone is welcome here!!!

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1/30/2012 6:55 pm  #31

Re: The aftermarket IRS picture thread

Ralphy -
That is the one !  In the C4 Community that is commonly referred to as a "Batwing."
Doesn't support the body  (so much) but offers a semi rigid "King Post Truss" to support the Diff/transaxle.   A clever bit of milling there! 

BTW --I find it increasingly interesting the number of uprights/Spindle carriers - that are all loaded in SINGLE SHEAR.  Like the GT40 referenced hub (? I maybe thought that was the McLaren - no biggie --an awesome design anyway!) shown in your pic above. 
Single sheer is less desireable and the webs are wide enough for other mounting options.   Seems like a bit wider web on the upright would easily accomodate a dual sheer mount for the LCA -- as done for the trailing arms. 
A bit surprising that - as I'd expect larger loadings on the Wishbones than the TAs. 

These are becoming my concerns as I spiral down the rbbit hole of preparing to buld my own uprights too!  Ahh - If I could only mill some billet Al blocks...

Cheers - Jim

Last edited by phantomjock (1/30/2012 6:56 pm)

UNDERCONSTRUCTION! Highly Modified C3 Corvette
         Dual Wishbone IRS w Subframe + Custom Uprights

1/30/2012 7:09 pm  #32

Re: The aftermarket IRS picture thread

I like how the C4 is done with the third mounting point directly behind the half shaft. Seems to me that would be the BEST point to hold the upright (strongest) in position. Same as Pier's, or C5. LOL! I understood and knew what you meant, Batwing. Later C3's had them also, no?

How about that wreck on I75?


Last edited by Ralphy (1/30/2012 7:39 pm)


1/31/2012 3:29 am  #33

Re: The aftermarket IRS picture thread

C4s only had the Batwing - some C3s have done the mod to put the C4 IRS on - There is a bit of modifying to work the dual TAs in.  Gotta cut and reweld the frame pocket and the positioning is of course a big thing.  I recall seeing a C4 Batwing modified to have narrower pickups on th eframe -- have to think where that was.

That wreck was pretty awful. The father of a Captian that works with me here, was in a big one yesterday too.  A bimmer did  a hard right "bat turn" into his trailer - flipped his boat off, spun the mess around - leaving the boat in the middle of the highway!  Some people just loose it.   
Fog and low vis are something you need to get the pace right for - but again, no accounting for someone else's mistake/stupidity.

Cheers - Jim

UNDERCONSTRUCTION! Highly Modified C3 Corvette
         Dual Wishbone IRS w Subframe + Custom Uprights

1/31/2012 7:33 am  #34

Re: The aftermarket IRS picture thread

Jim, I moved this/my discussion/response over to the Chevrolet picture thread. We are wandering off into Chevy on the aftermarket thread. LOL!
Click link.

Last edited by Ralphy (1/31/2012 7:35 am)


2/05/2012 2:46 pm  #35

Re: The aftermarket IRS picture thread

Gotta save this one. Will post pics later.

Last edited by Ralphy (2/06/2012 4:56 am)


2/08/2012 6:33 pm  #36

Re: The aftermarket IRS picture thread

Feast your eyes on this lucky soul!!cpZZ4QQtppZZ16

Last edited by Ralphy (2/08/2012 6:36 pm)


2/10/2012 7:08 pm  #37

Re: The aftermarket IRS picture thread

Last edited by Ralphy (2/10/2012 7:09 pm)


2/11/2012 4:00 pm  #38

Re: The aftermarket IRS picture thread

MAN!  Is that a Chassis member - or some massive stainless steel "4-H"exhaust system with side exits we can't see?!!!
That take LADDER - FRAME all too literally...

Cheers - Jim

UNDERCONSTRUCTION! Highly Modified C3 Corvette
         Dual Wishbone IRS w Subframe + Custom Uprights

2/14/2012 7:51 am  #39

Re: The aftermarket IRS picture thread

Here are some good pics of the Team 321 design



2/14/2012 12:18 pm  #40

Re: The aftermarket IRS picture thread

Thats pretty cool , It has to be about as minimal as you can get on framing .


2/14/2012 3:53 pm  #41

Re: The aftermarket IRS picture thread

Gotta admit -- He's pretty Clever. 
Like the bellcrank as support to the UCA, and the minimalist Upright design too.
I haven't been there in a bit -- Thanks for bringing that over Ralphy!

UNDERCONSTRUCTION! Highly Modified C3 Corvette
         Dual Wishbone IRS w Subframe + Custom Uprights

2/27/2012 2:35 am  #42

Re: The aftermarket IRS picture thread

I am surprised that no one noticed that both examples of the 321 suspension has the weight supported with a single Heim joint per side!  This would not be a problem if they were loaded correctly but they are loaded in a bending moment.  This is the wrong way to use a heim joint.   The load should always be parallel to the center line of the threads on both male and female Heims,   not perpendicular to it.  One hard slam in a pot hole deep enough to hit the bump stops,   and its all over.   
    The design with the shocks mounted out board would have to be the worse offender of the two.   Male threads make stress risers and dont resist much side  bending load.  If you combine that with the threads  stopping at the base of the bearing head and you have one hell of a stress riser!    Now apply a load perpendicular to the designed direction and you will soon have a failure.
   According to the bearing manufactures this is an example of how not to use spherical rod ends.
     PS  the clock on this web site is an hour ahead of west coast time.    its only 1:30 here

Last edited by tyrellracing (2/27/2012 2:39 am)


2/27/2012 5:16 am  #43

Re: The aftermarket IRS picture thread

I think PhantomJock and I discussed this in a round about way. We talked of, if using a Heim to go with a 3/4" for more strength. Knowing (assuming) it looks to be a weak area. Also by seeing examples as you pointed out, plus others. It must work?

Then also going back and forth in my mind. The Corvette design puts the load (coilover) on the upright not on a control arm. Weighing the pros and cons mentally.

This is a good point and good catch TR. At first thought you may think a racers suspension gets more abuse than a street car. However racers generally never see pot holes. A street car will more than likely see more abuse in ways a racer never runs into.

Last edited by Ralphy (2/27/2012 6:19 am)


2/27/2012 6:24 am  #44

Re: The aftermarket IRS picture thread

How much stress do you suppose the UCA's inner rear pivot takes? Having the leverage shortened with the coilover always loading on this point. At minimum this would be a high wear area for the 321 design.

Last edited by Ralphy (2/27/2012 6:26 am)


2/27/2012 11:49 am  #45

Re: The aftermarket IRS picture thread

Poor design in my opinion. Must be designed for an ultra-lightweight car. Looking at the acceleration loads I don't think that 10 ga. upright for the inner front top pivot is going to hold up very well, and if it goes the rear one goes right along with it. The bottom may be better but I don't see any gussets anywhere.

In all fairness, it is very much a challenge to design something like this from a clean sheet and not discover compromises. But basic fundamentals like proper loading and load spreading can't be ignored. If this was done professionally I'd certainly be looking for a new engineer at the very least. Looking at it I can't imagine that this is the case however, and the designer is still learning. He will definitely learn a few things on this one.



2/27/2012 1:47 pm  #46

Re: The aftermarket IRS picture thread

Jim B, that is what I said the first time Daze posted pics of the Team 321. Looks like it was intended for a light car.

Another bit a read about F1 moving the coilover off the suspension. It was not moved for reduction in weight. It was moved when they went to a high aero design to remove any aero effects. Found that interesting.

Last edited by Ralphy (2/27/2012 1:50 pm)


2/27/2012 2:41 pm  #47

Re: The aftermarket IRS picture thread

Yeah, if you're doing 200+ you don't want those gnarly things hanging out in the slipstream. The ratio change was supposed to help reduce the coil-over weight some but the linkage offsets it.



2/27/2012 9:11 pm  #48

Re: The aftermarket IRS picture thread

My thinking was rather than using a Heim for the upper connection to the upright,  I would be more inclined to use a uni ball pressed into a sleeve and retained with a snap ring.  Then that sleeve would be  welded to the now longer bell crank.  This added length would be virtually the same geometry as with the Heim  but would only be as weak as the gauge tubing used for the bell crank.  It would not allow the bell crank to be an adjustment point for alignment  but I dont think that would be wise since it would affect the leverage the load has over the coil spring.    As far as over all strength of design.  Street driven vehicles tend to see more harsh spike loads than many race cars.  Not too many huge pot holes at Portland International Raceway  yet thousands of them with in 5 miles of my house.  The suspension failures I have seen that were not from operator error were the result of spike loads caused by pot holes.  Its tough to design a suspension that can tolerate Oregon roads with out ending up being as heavy as a Sherman tank.   Again there has to be a point of compromise between weight and strength.    I have a great deal of respect for the designer that can build a suspension light enough to function over irregular roads yet tough enough to survive  real world abuse.


2/27/2012 9:49 pm  #49

Re: The aftermarket IRS picture thread

By all means it is easier to criticize the work of others than it is to create the design ones self.  Years ago I utilized a bell crank system nearly identical in concept with the 321 but with air bags  on a sand rail.  The reason for the bell crank was to gain 24 inches of wheel travel with 8 inches of air bag travel.  This worked fine at first but the intense loading at the pivot of the bell crank eventually led to stress cracks in both the frame as well as the bell crank its self.  After many repairs and redesigns I finally abandoned the bell crank design and went to 24 inch travel King coil overs attached directly to the uprights.. 
     Having the coil over's connected directly to the upright has to be the most sanitary way to support the vehicle weight on a IRS .  This leaves the UCA and LCA to support the natural suspension loads and none of the load carrying  chores.  When I was first going through the watts linkage on my uprights,  one thing I wanted to do was to get the LCA out of the load carrying business.  This would allow me to use a lighter LCA.   I tried many different configurations but found that my frame rails were in a location that made that idea impossible. I was able to move the lower shock  mounting location much closer to the upright but in the end they still are on the LCA.       I am willing to make some changes to my car but since I have no replacement rear frame rails, chopping up the rear frame rails wasn't one of them.

Last edited by tyrellracing (2/27/2012 10:27 pm)


2/28/2012 12:00 am  #50

Re: The aftermarket IRS picture thread

Well I have seen others use Heims successfully, I think. At least some of the Cobra guys have pics posted with them. Kirkham uses Heims, but not where the spring force is the greatest.

You also can see them used in a little different manner in this link. I won't post any pics so you can feel ill with envy sorting thru some of their open house pics trying to find what I'm talking about. LOL! See if you can remember what your looking for.

Last edited by Ralphy (2/28/2012 12:10 am)


2/29/2012 3:17 am  #51

Re: The aftermarket IRS picture thread

Yea I have seen i-1.25 heims used on v8 powered sand rails for front ball joints.   Loaded entirely wrong from the manufacturer's point of view.  These vehicles could safely jump distances of over 75 yards with at least  20 feet of air land over and over with out failure.   Just because it is wrong,  doesn't mean someone can not make it work.  I have broke a dozen or so Heim joints in the last 25 years.  Most of them were 1/2 inch and every one failed due to a side load.


2/29/2012 6:25 am  #52

Re: The aftermarket IRS picture thread

Several unique things here. First the Heims are rotated 90 degrees. On/off, power/braking in this configuration will at least prevent the forces from trying to push the sphere out the side. Then the UCA is 2 point mounted to the upright. Instead of the typical LCA being where the 2 points mount to the upright. Being that the UCA is the shorter of the two. Does this not add less un-sprung weight? Also The spring is loading on the upright, not on a control arm. So the weight from the wheel does not travel thru the Heim joints on the control arms. Plus you get an almost 100% use of motion having the spring mount all the way out.

Kirkham Billet Cobra Build PDF File.

Last edited by Ralphy (2/29/2012 8:52 am)


3/01/2012 4:01 am  #53

Re: The aftermarket IRS picture thread

The springs are attached to the uprights through linkage rods, Yes?   The control arms in this application do not have any serious side load.  Even braking loads would be like pulling at one point of a triangle which would apply tension to one side and compression to the other.  The orientation of the heim really did not make a whole lot of difference as to failure.  I have never seen a ball pulled out of one yet I have seen them loaded in a direction that one would assume would dislodge the ball that  snapped off the head at the base of the threads.  The Heim as far as I have seen when in decent condition dont allow the ball to escape before the stem fails.
      Since the weight load path does not go through the control arm like it does in a cantilever type method similar to every other IRS with springs on a control arm.  The Heims on the frame only have tension or compression loads with no side loads to speak of.   I did not see weather or not Kirkham used heims for ball joints but if so they would see side loads only from braking and acceleration as long as the rods supporting the weight are attached to the upright.   In the application described the side loads are governed by tire adhesion and as such will almost always be lesser than side loads generated by supporting the vehicle weight.  If they chose to connect the push rod to the LCA on the front with a heim for a lower ball joint, Then in my opinion they chose poorly.   Just because it looks pretty doesnt mean it is strong.     Strength of design is the difference in weather its a driven vehicle or a trailer queen.    The billet Cobra shown probably will never see more than 100 miles in its entire existence and that will be generated by moving the thing on and off the trailer to its pedestal for viewing.  As such it could be built out of balsa and tin foil and have the same wow factor.    Just my personal opinion.

Last edited by tyrellracing (3/01/2012 4:10 am)


3/01/2012 8:22 am  #54

Re: The aftermarket IRS picture thread

Come on now! LOL! I'm trying to make a pitch here.

But really, I think those are Heims in and out. If you go to the link, you'll find a pic of the car being scaled. It weighs 1,800 lbs. I don't know why a Heim would break in one direction more than another when all is pretty equal 360 degrees. However turning it 90 degrees does eliminate the stress pushing out on the ball.  Using a large diameter flat washer may be prudent also. So if it were to come apart it would still be trapped. That car was tracked by pro drivers also. The article does say it is one of a few cars that runs out of motor before it runs out of suspension.

Another thing, I think that suspension is used on more cars than just the billet project. Thought I saw a pile of those uprights in a pic.

Last edited by Ralphy (3/01/2012 8:42 am)


3/01/2012 6:53 pm  #55

Re: The aftermarket IRS picture thread

I guess I should restate what I was trying to explain poorly.  The spherical rod end is weakest in a side load and will shear in any direction that is perpendicular to the stems center line.  I have seen these rod ends used wrong more often than right.  They are just too handy not to.  I have been guilty of this more times than I can count.  However using them as a lower ball joint is really taking an unnecessary risk that could be deadly if it were to fail at the worst moment.  Weight saving is not worth the risk of loss of life.   There are just too many good light weight  thread in type ball joints available that are stronger and nearly the same weight as a same size rod end to take the risk.   The Billet Cobra is with out a doubt a work of industrial art.   Since it is a show car that would be ridiculous hard to get clean,   I dont think the owner will drive it much.  Could you imagine cleaning all the nooks and crannys after a short drive and getting caught in some rain?  Clearly Kirkham builds lots of nice cobras and probably have been doing it for years.  The billet car was a demonstration of what they can do when they have a customer with unlimited funding.           Kirkham's  CNC machining ability's are with out question,  out standing.     
         Realistically this vehicle will be their signature piece for advertisement.
    As for using washers to  trap in the ball.  It definitely cannot hurt.  I have seen the results of so many poorly engineered uses of rod ends that I can say with confidence that having the ball come out of the rod end would be a VERY rare type failure.  Even the cheapest ones break at the stem.      just like the high dollar chromally ones.


3/02/2012 6:35 am  #56

Re: The aftermarket IRS picture thread

They really aren't made for any loading other than push-pull. Once you start applying side leads, whether through the bore or perpendicular to it, you compromise the design, due to the large number of stress risers created by the threads on the shank, and it takes a lot of extra beef to overcome that. Sure, you can go oversize but that sort of defeats the purpose doesn't it? It's clear that heim joints are over used, often in places where better solutions exist. On race cars it is easier to get by with it because everything gets inspected regularly over a comparably short service life, but where I see a real problem is in street use where something is built just like it's track equivalent and then expected to last like any OEM suspension, despite the fact that the heim has no provision for lubrication or for keeping dirt out, and this is a formula for disaster. Sure, you can install zerks and side seals but they really aren't all that effective. The thing is, it really isn't that easy to design a joint that never sees any side loading when you have an upright that wants to move up, down, in, out, forward and back, to say nothing of torsion loads. Small wonder that the OEMs resort to rubber bushings.


Last edited by Jim Blackwood (3/02/2012 6:46 am)


3/02/2012 4:02 pm  #57

Re: The aftermarket IRS picture thread

Jim Blackwood wrote:

Small wonder that the OEMs resort to rubber bushings.Jim

1. Cheaper -- "...ahh it's a Profit Deal."  (was that from a Steve Martin film?)
2. Noiser - bad for profits.. who wants a noisy suspension in the family grocery getter?
3. More inspection and liability -- Cha-Ching!

Now,  spherical bearings - like Johnny Joints - or Spohns are more robust - not as noisey, and sealed better than Heims - but much more $ and significantly larger/heavier. 

One trade-off or another. 

Cheers - Jim

BTW - I'm getting close to a few CAD representations of several Upright Designs I am considering.  Try and get done and posted this weekend -- got to cut and burn some metal!

UNDERCONSTRUCTION! Highly Modified C3 Corvette
         Dual Wishbone IRS w Subframe + Custom Uprights

3/04/2012 12:56 pm  #58

Re: The aftermarket IRS picture thread

I would be scared if I could hear my suspension, Rod ends and all over the rumble of my three inch exhaust and flowmaster mufflers.  I tend to feel the looseness of worn parts from driving and knowing when their is the slightest change.  It doesnt take much free play in a suspension pivot to make the feel of the car change.  When the vague feel of rubber bushings has been removed the accuracy of suspension feed back to the driver enables the driver to know exactly where the limits of traction are.  Any free play here would nullify this sensitivity or at the very least cause a sudden shift during the transient portion of the corner entry.  I  had a car that when at the apex of a turn you could feel the inside front tire flutter from free play.  This turned out to be a worn ball joint that allowed 1/8  change in toe. Combine this with built in ackerman angle and the result is some wicked toe out in a sharp corner.
    Both Jim's are absolutely right with their points.  I don't care for OEM  rubber bushings  but they are required to isolate suspension noise and ride harshness.  The general public does not like harsh riding cars so they would not sell very well.  The average driver doesn't check their oil as often as they  should let alone the suspension.  Heims have no method for keeping the road grit out of or grease in the bearing surfaces so they will tend to have a short service life in daily driven use.  Any one using rod ends in their suspension should have a inspection schedule  like at every oil change.


3/04/2012 1:26 pm  #59

Re: The aftermarket IRS picture thread

tyrellracing wrote:

Heims have no method for keeping the road grit out of or grease in the bearing surfaces so they will tend to have a short service life in daily driven use.  Any one using rod ends in their suspension should have a inspection schedule  like at every oil change.

That's not true. There are several types in fact.

Last edited by Ralphy (3/05/2012 5:34 am)


3/05/2012 6:35 am  #60

Re: The aftermarket IRS picture thread

Those would help, though the thin rubber would be a little fragile. The washers aren't effective at all if there is any angle in the joint.

Here's another idea for camber control:
Claims to be Patented though (no number given?), so to use it would require some careful reading.


Last edited by Jim Blackwood (3/05/2012 6:36 am)


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