Why not that many IRS in here

[novanutcase]

Sure....shoot it in the same light and use the same aperture settings.



Oh wait....thats kind of like the IRS. Use the same geometry and check whatever other conditions affect the performance of the IRS and get them as close to what that particular IRS was designed for and you should get pretty damn near the same performance.

As far as the "quote", if it can be done with a stick axle then, again, why isn't indy using them? Truck arm? Used only because it is required by NASCAR rules. I'm sure, if given the choice, pretty much every team would opt for a different type of rear end setup.

Look....I'm not here to argue the virtues of this setup versus that setup as I think we can all agree that it depends on many factors, most importantly what you will be doing with the car. I choose to try and push the envelope in terms of design and what can and has been done to these kinds of cars. Now....when I say "push the envelope" I am in NO WAY considering myself superior to anyone elses build. I just feel that not many people have explored this option for fear that it is "too costly and too hard to figure out". I, for one, would like to see if it can be done and if I get bish-slapped for it so be it but at least I can say that I tried instead of getting in line with everyone else. What fun is that? Isn't that the core of what we are trying to do with PT? Improve our cars in ways that people haven't thought of or have been too afraid to do? Thats what pushes our beloved hobby forward.
BAZ I completely understand what you are saying and many times I have thought "Why am I torturing myself when I can call Art Morrison and he can build me a triangulated 4 bar that will outperform most corvettes!" but from all the research that I have gathered so far the pros (and cons) of IRS keep rising to the top of the heap. I just got to see if it will work. Granted, if your build budget doesn't allow it then, by all means, you should stay in the "tried and true" area so that you don't unnecessarily blow money on something that "might" work. For me, I have the opportunity to see if it works so I'm going for it!

[baz67]

Because they need the axle out of the way to get the car that low. He will not get his car any lower with an IRS than he can with a stick axle.

The IRS-photography anology is crucial here and goes towads answering the original questions as to why more PT cars do not have IRS. So you feel that everthing being equal that one person can perform as well as another. For that to work operator needs to be able to utilize the equiment to its fullest. Hense my photography referance. I know I cannot hop into Michael Schumacher's car right after he gets out of it and post lap time even remotely close to his. That is one reason for the lack of IRS is our PT cars, our hack driving skills cannot take advantage of it.

As for getting the same shot with the same lite and apeture setting, I wish that were true. On Bill Howell's shoot I was able to shoot side by side with Johnny for some shots and even though mine were good his were better. Why? He knows his equipment and how to use it much better than I do.

[novanutcase]

Because they need the axle out of the way to get the car that low. He will not get his car any lower with an IRS than he can with a stick axle.

The IRS-photography anology is crucial here and goes towads answering the original questions as to why more PT cars do not have IRS. So you feel that everthing being equal that one person can perform as well as another. For that to work operator needs to be able to utilize the equiment to its fullest. Hense my photography referance. I know I cannot hop into Michael Schumacher's car right after he gets out of it and post lap time even remotely close to his. That is one reason for the lack of IRS is our PT cars, our hack driving skills cannot take advantage of it.

As for getting the same shot with the same lite and apeture setting, I wish that were true. On Bill Howell's shoot I was able to shoot side by side with Johnny for some shots and even though mine were good his were better. Why? He knows his equipment and how to use it much better than I do.

OK.....I guess I am starting to see your logic although I will still argue that system for system IRS has more to offer in terms of performance. As far as the operator, Yes, much of what is wrenched from the car depends on his skill. Although, if I was given the choice to choose only one car to be able to improve my skills it certainly wouldn't be in the trainer car rather than the full blown one as I would outgrow it at some point and be disappointed I didn't choose the full blown. I think you should build as much car as you can and build your skills parallel to that car. JMO!

BTW - Any chance of us taking a beer break! I'm buying!

[David Pozzi]

IRS suspensions have less unsprung weight, so they are better over bumps, however they do not have a way to use the torque reaction of the differential to help plant the rear tires. They can only use the geometry of the links and reaction forces of the tires on the pavement to generate the anti's. They have less antisquat/antirise.

In classes like Trans-Am or IMSA where the Corvettes could use either type sytem, the stick axle has proven to be as competitive on smooth race tracks.

On formula race cars IRS is needed, the cars are very light and low unsprung weight is very important the lighter the car, also they have 60% or so rear weight bias, so rear traction is pretty good.

[Norm Peterson]

. . . I feel that all other forms of rear suspension(3 link, 4 link, 4 bar, ladder bar, PHB, watts, etc.) are all just bandaids for a system that is old technology. Yes, the bandaids work REALLY well but, as I said before, if you are just trying to make your car handle "good enough" then a stick axle is your ticket but if you want to try and push the envelope then I think IRS is a good place to do that.

That list of yours is one of different configurations; some of which do certain things better than others do (and vice-versa). They are NOT "band-aids", unless you're considering combinations like a PHB with leaf springs. Anyway, there's a comparable list of IRS configurations (SLA, Chapman strut, semitrailing arm, DeDion, to name a few).

Edit: Plan on spending a lot of time getting the geometry somewhere near right. Tuning efforts centered around springs, sta-bars, and shocks won't do much to fix (for instance) a poor toe steer curve or (another example) wild roll center migration. Don't take this as negativity. Just a friendly warning to not underestimate what's involved. My normal bottom-line statement on this topic is that a well-done stick axle will outperform an indifferently done IRS, if only for the greater confidence it provides.


Norm

[vintageracer]

If you wish to "correctly" install an IRS in a Chevelle or any other non IRS equipped car, design a new frame with the proper suspension points, call Art Morrison and have him mandrel bend the rails/crossmembers and get to welding. This is the only way you will have a proper setup specifically designed for your application. Forget about using "street rod supplier" front and rear suspensions. They are for what they are sold, street rods! The best available OEM suspension to "design" your frame around would be Corvette. If you are willing to "cut" your body, use C5 suspension. If you are not willing to "cut" your body, you will less trouble "packaging" the rear suspension with C4 suspension. In both cases it is easy to convert to Coilovers for adjustablility.

Lower roll center, more caster, taller spindles yadda yadda yadda an IRS conversion may/can provide is all great however there are VERY few individuals on this board with the fabrication skills to properly install and set up an IRS in a non IRS equipped car. I also doubt there is ANYONE on this board with the driving skills to take advantage of the benefits this expensive modification will provide.

[93Polo]

I was wondering if we could go C-5 all around? I'm thinking C-5 IFS and C-5 IRS. 21st Century makes an adapter where the 'vette trans goes so that we can still use a drive shaft and use the C-5 diff. What do you think?

After owning a C5 I would look into other options for the diff., a Ford Cobra 8.8, or CTS-V diff may work. The C5 guys are adding bracing to keep diffs alive in higher HP cars. The Ford 8.8" and 9" diffs also have more and cheaper gear ratios available.

The early CTS-V diffs are weak but the newer ones are tougher. Shops are also working on adding Ford 9" diffs into the CTS-V IRS. The topics were on LS1tech. I would not be surprised if the C5 half shafts could easily be modified to work with the CTS-V diffs.

[silver69camaro]

I always wonder how these IRS vs. Solid discussions get started. Are we approaching the handling limit of a solid axle suspension? What's really is the problem with a solid axle? How much are you going to gain from a C5/Cobra IRS from a really good 3-link? Is the cost worth it?

Or do we just want bling?

[baz67]

I always wonder how these IRS vs. Solid discussions get started. Are we approaching the handling limit of a solid axle suspension? What's really is the problem with a solid axle? How much are you going to gain from a C5/Cobra IRS from a really good 3-link? Is the cost worth it?

Or do we just want bling?

My thoughts exaclty Matt.

[93Polo]

The stock GT solid axle setup isn't a good comparison against the 99+ Cobra IRS... now, driving a 'Stang with a Griggs TA/PHB rear setup compared to the Cobra IRS would be a good comparison. I think you would be very surprised.

The Cobra IRS was a poorly design piece. The IRS hangs on a cradle that uses some of the original 4 link mounting points with rubber bushings mounting the cradle to the unibody and then the a-arms have more rubber bushings mounting the a-arms to the cradle. It has to many bushings allowing flex which results in wheel hop.

[hooligan68]

This thread got me to thinking. Being a true blue Mopar man, I'm thinking that maybe adapting the rear end of an SRT8 Charger might be the way to go. However, I've not had the time to properly research this avenue and at this point, don't see when I will. Any suggestions as to where to start this research would be helpful and greatly appreciated.

[hssss]

and just went thru the same arguments/discussions. From my research it seams that a 3 link with Mumford link for lateral location is probably the best solid axle setup for my application. The choices of axles came down to an 8.8 or 9" either of which needed some level of aftermarket parts with the 8.8 winning due to less parasitic loss. I had forgotten how bloody heavy the 9" is till I tried to lift a complete onto onto my welding table for dummying up parts. In my case the unsprung weight would be a large percent of the total weight, not a good thing. Some of the arguments I was using in favor of the solid is CO$T, weight and complexity of the IRS vw the solid. By the time I had an 8.8 solid in proper condition, aftermarket axles, 9" ends, and a Torsen (needed by both) I would have about the same $ in both. For the IRS there is a design on the web, Rorty, for use in the 7 that could probably be adapted to others. I'm actually doing 2 7s, one for my wife and one for myself. The first, Put-Put is a rebodied MII with a Versailles setup with a 3 link. The other, Shagnasty, MN12 spindles and MN12/Cobra/Explorer IRS. As far as cost the IRS probably will be about the same if not lower cost. The parts: MK VIII spindles $26 Ebay, 2000 Cobra R diff $79 Ebay with 3.55s (will attempt to sell the posi to recoup the cost of the Torsen), 03 CORBA (Terminator) half shafts $150 C-C (one has DSS level 2 shafts, $99 to do the other), Torsen T2(OEM) 157 Ebay. What I wind up with is aluminum 3 point knuckles with 10.5" disk brakes, 28 spline hubs at the wheel hub and 31 spline at the diff, a setup which is used in anything from a BEC LC7 to a relatively stock 03 Cobra, this with 315 35 17s in a 1400 to 1600 lb car should be relatively unbreakable. With the aluminum chunk the total weight should actually be lower than using an 8.8 solid and the unsprung weight is MUCH less. I didn't even consider the C4 stuff because of breakability, 4 speed cars are D44 and the 8.8 is at least 30% stronger and the auto is a D3? which is even weaker, CO$T and I don't like using the half shaft as a suspension member.

Factory 5 Cobra


Deman Lotus 7 BEC

2000 Cobra R and Lincoln MK VIII with Explorer rear cover

A note DSS in in the final phases of offering an 8.8 chunk for the GTO.

[jfman]

Very nice looking setup !

Thanks for chiming in !

[Cometose]

I always wonder how these IRS vs. Solid discussions get started. Are we approaching the handling limit of a solid axle suspension? What's really is the problem with a solid axle? How much are you going to gain from a C5/Cobra IRS from a really good 3-link? Is the cost worth it?

Or do we just want bling?

My interest in IRS is how well it handles/rides over typical poorly surfaced roads(pot holes, patches,etc...since that's what I see before getting to any smooth roads) compared to a 3-link.
I'll probably go with a 3-link in the end because of the complexities of doing an IRS install correctly

Joe

[novanutcase]

I guess I should have explained my build before battling with BAZ which would have made much more sense to everyone. I had been talking to Wayne Due about doing a full perimeter chassis and this is why I felt that IRS was a good choice for me since with the full frame I had the freedom of setting it up correctly and not having to deal with the packaging issues. Now that Wayne is not able to do this I have been speaking to several chassis builders and am in the process of trying to choose who will be that person. I guess what I am looking to build is a car that can cruise like a lexus and still be able to auto-x/road race. Granted, I realize that the expense will be more but I would really like to see if I can get the best of both worlds. Is it bling? I guess in some respects. I know that a 3 link will give me comparable performance and I will probably not be able to drive the IRS to its designed limits but I really want to try something different besides the 3 link/watts setup. I have had several discussions with Mark Magers about this very setup and although it is a very good system I really want to see if I can get the IRS to work. I think if I can it would really open the doors to other manufacturers looking at packaging something like this to make it easier for someone to go this route.

[Twin_Turbo]

My corvette came stock with IRS (although a petty crappy trailing arm setup) , I first changed it to a 5 bar but then decided to build a double a arm setup.

[wendell]

Twin turbo,
Your tires don't have tred on them. I'm interested in your porject. care to give us the scoop?

[Twin_Turbo]

They are slicks that's why they don't have thread. Pics are here:

http://members.home.nl/m.b.p.jongman/?C=M;O=D

[Mean 69]

TT, I think Wendell kind of knew what your tires were all about.... Bitchin car! Have you had the double wishbone setup on the road yet?

You are definitely my kind of guy. Great ideas on that car.

Mark

[wendell]

Seems like a bunch of effort concidering you're not going ot get any traction with those tires. And don't even think about driving in the snow. Good luck, you're going to need it.