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

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8/24/2013 1:03 pm  #1

noob, seeking some general IRS opinions

Hey all.  First post.

I am coming off years of experience with RWD muscle cars, mainly old 60s/70s stuff.  I am considering trying to custom-fab an IRS for a car of this era.  But I am wondering about how it changes the feel of the car.  The only RWD IRS cars I have had were very modern.  They are not a very viable comparison because there is way too much else about the car that was too far removed from an old musclecar. 

I really love the old-school feel of the 60s/70s stuff. Very mechanical, you feel the torque . . . they don't feel like "the car is an extension of the driver" at all, they feel more like you are riding a bull.  Modern cars are so fast but they manage to bore you while they do it. 

I guess I am wondering how much of that feeling is related to the SLA setup, between the torque twist upon hitting the throttle, to the heavy unsprung weight in the back, etc.  I wonder if I will kill too much of what I like about the old car to update it to an IRS. 

Who has done this kind of conversion and lived to tell about it?  Did it "modernize" the feel of the old car dramatically?  Can you describe it? 

I am picturing an IRS that feels factory built, if that makes any sense.  Rubber bushings on the arms, no super lightweight fragile components, ball joints rather than heims, lots of ground clearance and wheel-travel like the stock SLA had, etc.  When I say "converting to IRS" I don't mean taking the whole chassis & car in a different direction while I'm at it.

Thanks for any feedback.


Last edited by thedude (8/24/2013 1:05 pm)


8/26/2013 10:50 am  #2

Re: noob, seeking some general IRS opinions

First - Welcome.
Second - I can tell you a bit about my build.  I'm putting a Jag IRS into a '59 El Camino.  Main thing I'm looking for is ride comfort.  I'll also be updating the front suspension with tubular control arms and coil overs front and back.  The front spindles will have ball joints but I'll have heim joints for connecting the trailing arms to the frame.

If you really wanted to keep original mount points and hardware, you'd be keeping the bird cage (really easy to mount into a frame) and the trailing arms with rubber bushings when connected to the frame.

This article may have what you're looking for:

Good luck!


8/27/2013 2:42 am  #3

Re: noob, seeking some general IRS opinions

Welcome Aboard!
One advantage to an IRS - yu can adjustthe "feel" to how road holding to sloppy you'd like it.  Especially if you do the designing.  Before you take the plunge however, have you done any upgrades to teh current suspension?  Might find a lower cost approach by using some coil overs now (and then integrating them later).
You could use Kohnny Joints - or Spohn  spherical joints for a better more consistent "feel" over Heim joints in the build - but take care - again CHA-CHING = $!
Just so many choices and much to learn.  You've come to IRS Central - welcome.

Cheers - Jim

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

9/02/2013 12:33 am  #4

Re: noob, seeking some general IRS opinions

Upgrading the existing rear end -

I'm considering an IRS conversion for the deeper things it fixes - reduce the unsprung axle weight and stop the rear end from breaking loose on mid-corner bumps.  So there aren't really any lesser steps worth taking before biting off the whole thing. 

I'm dealing with a muscle-era Mopar so the basic front suspension geometry wasn't bad to begin with.  The stock caster & camber settings are way off because the factory was designing everything to accomodate bias-ply tires and manual steering boxes.  But the more dynamic stuff (roll center, camber gain, anti-dive, etc) is already decent.   

That old Colin Chapman quote about "any suspension design will work, if you don't let it"  - my thinking is pointed totally the other direction.  I want something that moves freely, isn't too stiffly sprung, and is stable & predictable no matter where each wheel is or what they are rolling over.


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