Rear Suspension choice: IRS vs. 3 link?

[Jazzman]

First, a thank you to all the friendly members of the Arizona Cobra Club for their wisdom yesterday. It was great to meet all of you. Special thanks to Scott who let me sit in his Cobra. (My very first time!!) I appreciate the combined wisdom that you were more than willing to impart.

After polling the members I met and reading many posts on this forum, I seem to be coming to the following conclusion: The independent rear suspension is a nice option if a)you can afford it, b) you want the best possible ride, and c)you want to maximize resale value. However, for basic performance and general street use, it is an expensive option that can be just as easily, and less expensively, replaced by the 3 link fixed Ford Rear End with coil over shocks.

Do you concur with this statement? At the moment I plan to go the second route, and later add add the IRS if I decide I really need the improved ride. (It sort of depends on if my wife is happy enough with the fixed rear axel!)

You comments and wisdom will be greatly appreciated.

Jazzman

[DaleG]

I recall a similar question posted recently and a consensus (as you said) that IRS for street and 3-ling for track. Having said that I had 3-link on my MKII and am doing the same on my MK4. 12,000 miles on the MKII and I liked it. I have not driven a IRS roadster, so cannot offer a comparison; lets hope others can.

[Gumball]

Before I ordered my car, I rode in both IRS and 3-link cars on the street and the track. Based on that, I went with the 3-link due to it being - in FFR's words - the performance option.

As for resale, I would agree that in general, a car with IRS will have somewhat greater resale or, given equal quality builds, it could make the car more marketable. But, I think a really well built car will not suffer because it has the 3-link. Would IRS add a little value to my car? Sure, but it would also have cost a little more from the beginning, so I think the financial argument is a wash.

Remember, too, that IRS is a bit more complicated to install and set-up.

[2bking]

Do you concur with this statement? At the moment I plan to go the second route, and later add the IRS if I decide I really need the improved ride. (It sort of depends on if my wife is happy enough with the fixed rear axel!)

You comments and wisdom will be greatly appreciated.

Jazzman

Going from a 3 link to the IRS can be done but is expensive. The IRS is about a $4k cost now and about a $3.3k cost later assuming you reuse the gears and differential parts. I don't think the brakes will transfer due to the mounting scheme so that's another cost. There is a lot of stuff that would need to be removed as well as maybe the body just to weld in the IRS frame. The ebrake cables may have to be replaced. Then you get to reroute the brake lines as well as maybe the fuel lines. If the battery is in the trunk???? You should pick one or the other and not look back.

[edwardb]

First, a thank you to all the friendly members of the Arizona Cobra Club for their wisdom yesterday. It was great to meet all of you. Special thanks to Scott who let me sit in his Cobra. (My very first time!!) I appreciate the combined wisdom that you were more than willing to impart.

After polling the members I met and reading many posts on this forum, I seem to be coming to the following conclusion: The independent rear suspension is a nice option if a)you can afford it, b) you want the best possible ride, and c)you want to maximize resale value. However, for basic performance and general street use, it is an expensive option that can be just as easily, and less expensively, replaced by the 3 link fixed Ford Rear End with coil over shocks.

Do you concur with this statement? At the moment I plan to go the second route, and later add add the IRS if I decide I really need the improved ride. (It sort of depends on if my wife is happy enough with the fixed rear axel!)

You comments and wisdom will be greatly appreciated.

Jazzman

I agree with the advice you've been given so far -- decide which one you want and go with it for good. Switching from solid axle to IRS, while possible and has been done many times, is expensive and not particularly easy. It involves not only different axle and brake components, but also different mounting points on the chassis (think welding). Plus other possible differences like brake lines, fuel lines, battery mounting, etc. I also agree that resale value is more about the quality of the build. A well built 3-link will still command very good resale. It's the number one choice of builders for a number of good reasons.

Here's my opinion FWIW: No question IRS is the best riding and the most authentic. Plus has a certain "cool" factor. But a well executed 3-link (or 5-link) solid axle is a very good choice and I challenge that your wife would find this a difference to ride in the car versus not. These cars are small, loud, and short wheelbase no matter which suspension. The sun and wind while cruising is the same either way. Big rigs look tall and are loud. There's a lot of sensory input while riding or driving, and frankly ride quality is not the only one. Maybe not even the main one. Some of the early versions, especially with donor suspension components, were admittedly marginal at best. But the current versions with aftermarket parts, including quality coilovers, ride remarkably well. I'm frankly amazed at how well they ride, no matter solid axle or IRS. The ride is firm, but not harsh. But for the reasons listed, most people are not driving them long distances. We've done cruises of 200+ miles. We are beat up from sun, wind and noise way before ride quality. My wife has never complained about the ride. We're on our second. Both solid axles.

[Dan Babb]

The other factors mentioned ( sun, wind, loud engine, giant big rig wheels rolling by your head ) will be contribute more to someone's dissatisfaction than your rear suspension choice. My wife hates my cobra for the reasons above and even if it handled like her Porsche, she wouldn't like the car.

Spend some time finding someone to give your wife a ride in the car and go from there. I think you're way better off picking one suspension option and sticking with it since doing the IRS swap isn't a bolt-in deal.

[Shelby Dave]

Hi guy's!
Im brand new here. I am starting a build of a 1989 Bennett Cobra. The car has not had a thing done to it so far. It is designed for a MG front suspension and a Jag rear and that is how i intend to build it. I have the stock non modified MG front and a XJS rear. I am now looking for a good source to shorten my XJS rear to the required XKE dimensions, or buy the parts to convert. I want to keep the inbrd. disc brakes. I am also looking for the suppliers of the components to upgrade my front MG suspension for my FE, ( brakes, coil over's, 5lug conversion etc.) I so far plan on using my 4spd top loader also with hydraulic clutch.
I have not found (so far) an old school build like this. I find it fascinating people are using Subaru's as donor cars. Wild.
I have all of the original documentation from Paul Bennett but that does not include a lot of technical info. I did buy someones Zerox copied assembly manual on line and it is about 65% helpful. His black and white pictures are poor, but the text is readable.
As my status of "Junior member" improves I will start my own thread and share some pictures.
Anyone out there with a bennett Cobra with advice on my build? I'd like to say Hi. The day I bought it . DCP_3204.JPG

[Dan Babb]

Shelby Dave....our resident expert for questions on different manufactures is Bill (MrMustang). Try to send him a private message and see if he can help you out.

Here's a link to his profile page.
http://thefactoryfiveforum.com/member.php?43-mrmustang

[Shelby Dave]

Will do, Thanks Dan

[edwardb]

I find it fascinating people are using Subaru's as donor cars. Wild.

You do realize that's a completely different car (818) not related to the Cobra replica? Nothing common other than the same company. Just making sure...

[Jeff Kleiner]

Shaking the cobwebs out of the old memory banks here but as I recall Paul Bennett worked with Steve Arntz when the Arntz/Butler cars were being produced and then set out on his own. The Arntz Butler cars used MGB front suspension and Jag rear so it sounds like what you have could well be an extension of that philosophy. The Arntz/Butlers had the engines set waaaaaaay back and by the looks of the long nose in your photo that characteristic may have been incorporated as well. That's about all I can recall, maybe if Bill chimes in he'll have more.

Jeff

[skullandbones]

Hi Jazzman,

Sorry I missed meeting you at the HD show.

You should plan on what you really want up front if it is between the IRS and 3 link. It would not be that easy to transition after the fact. If you look at the KISS principle, you would probably go with the 3 link without a second thought. I did a bolt in three link of my own design (with help from my friends). I also added a watts link instead of the PHB. If you decide based on performance, you should think about that since it will give you adjustability that you will not get with the IRS or FFR 3 link. White Line has a Watts link that bolts on, I think. So it would be a 2 step process if you choose. The advantage is you can move your geometry up or down depending on the need. I really don't think most people will care about the difference that this would add incrementally but if you are leaning toward the performance side, it is worth considering while you are still in the planning stage. Also, Gordon Levy has a very nice 5 link that requires some welding but would add needed adjustability from site to site for tracking and the like. Even if you go with the FFR 3 link you might consider changing the fixed PHB to one with some adjustability later. Good luck with whatever you decide. WEK.

[Avalanche325]

I literally had a couple sleepless nights on this decision.

A couple calls to FFR to different people both stated that IRS is the comfort suspension. 3-link is the performance suspension. I said that I was going to autocross and do the occasional track day. Their immediate response was "You want a 3-link". To back that up, any time FFR does a performance challenge, like against the original or the Lamborghini, they show up with a 3-link car. They actually ride surprisingly well.

[Jazzman]

As usual, this forum is a wealth of knowledge. I have decided to go with a three link for several reasons: cost, relative simplicity of install, and the majority of people that I have access to are knowledgeable about the 3 link. My bride of 27 years loves to ride with me on my Harley, so the wind, noise, heat, semi-trucks, and other assorted challenges will be no big deal to her. (She did say I had to keep my Harley and add the Cobra. Great wife, huh!!)One more decision on the build sheet settled, only half million to go!!

SkullandBones: We seem to have an amazing ability to miss each other!! I hope we can finally meet next time. I will keep my eyes open for the next event. Perhaps then you can translate most of what you posted into some form of English that I can understand!! What in the world is a watts link or a PHB?!!

Thanks to all!!

[edwardb]

As usual, this forum is a wealth of knowledge. I have decided to go with a three link for several reasons: cost, relative simplicity of install, and the majority of people that I have access to are knowledgeable about the 3 link. My bride of 27 years loves to ride with me on my Harley, so the wind, noise, heat, semi-trucks, and other assorted challenges will be no big deal to her. (She did say I had to keep my Harley and add the Cobra. Great wife, huh!!)One more decision on the build sheet settled, only half million to go!!

SkullandBones: We seem to have an amazing ability to miss each other!! I hope we can finally meet next time. I will keep my eyes open for the next event. Perhaps then you can translate most of what you posted into some form of English that I can understand!! What in the world is a watts link or a PHB?!! Thanks to all!!

PHB = panhard bar or rod. it's the diagonal rod on the 3-link suspension setup.

Watts link = basically two panhard bars with a pivot anchored on or near the differential. Typically part of a 5-link suspension. This is the Gordon Levy 5-link from my Mk4 build. Not the best pic because the suspension is hanging with the chassis on jackstands. The arms are parallel to the ground when it's sitting on the suspension.

[clancypm]

Ok have to ask. I was planning on using the 4link rear suspension off of my 96 svt mustang cobra donor but I never see anyone talking about using that set up. Why?

[Jeff Kleiner]

Ok have to ask. I was planning on using the 4link rear suspension off of my 96 svt mustang cobra donor but I never see anyone talking about using that set up. Why?

Ever heard the term "snap oversteer"? If not search here and on the other forum...

Jeff

[edwardb]

Ok have to ask. I was planning on using the 4link rear suspension off of my 96 svt mustang cobra donor but I never see anyone talking about using that set up. Why?

To follow-up on Jeff's response, the 4-link setup is considered the lowest performing of the options. Due to the geometry, it can bind up and cause unpredictable behavior. For straight ahead driving it's strong, but start twisting it and getting towards the limits, and not good stuff can happen. The same reason the 3-link or 5-link mods are also popular on the Mustangs. A donor build 4-link is generally considered the weakest of the lot. With aftermarket parts, e.g. trailing arms, bushings, coilovers, it's better and can be OK if not pushed too hard. With the Mk4, the chassis can handle either 3-link or 4-link. So it would be possible to start 4-link and upgrade later. But recognize there are limits, especially with a pure donor setup.

[2FAST4U]

Go with the IRS

[Avalanche325]

Go with the IRS

....unless you are heading for the track, or autocross, or drag strip.

[rich grsc]

....unless you are heading for the track, or autocross, or drag strip.

Well I think he was mostly considering a street car….go with IRS

[Avalanche325]

Well I think he was mostly considering a street car….go with IRS

Looking at my previous comment, I meant it to be true but a little light-hearted, but it may have not come off that way. Sorry, 2Fast, if that sounded unfriendly.

OP,
The 3-link doesn't seem harsh at all to me, and I normally drive Infinitis and BMWs, which are firm but not harsh. But, IRS is the comfort version. It would be interesting to get a ride in both back to back. I am also in the boat of my wife has not complained about the ride, just the wind and noise.

[skullandbones]

Hi Jazzman,

We do seem like opposing magnets! However, we will get together soon. I want to show you my version of the 5 link and give you a ride. I did a track day and it handles very nicely. I will have to let you decide how the ride feels. I'm so used to driving the 4x4 Nissan truck, Rav 4 and other pickup trucks that my butt has become attuned to it. The 4 link ride was also a little "truck like" but the 5 link is less harsh on the butt. Mike has an IRS and so you can do a side by side test to see for yourself.

See you later,

WEK.

[Jazzman]

Thanks WEK. I will look forward to it. Until this past year, trucks were always my primary vehicle. Now I have become spoiled by my BMW X5. I could be entirely wrong, but I can't imagine there is more wind or a rougher ride than on my Harley.

Given the traffic around the Superbowel (no that is not a typo!!) and the Phoenix Open, not to mention the rain that no one seems to know how to drive through, this does not shape up to be a good weekend for driving. Be safe out there!!

Jazzman

[mcwho]

I think it has somewhat to do with what your type of driving expectations may be.

I grew up with Touring type of cars with IRS. Such as Alfa Romeo, Fiat 124 and Sunbeam Tiger. One of the best suspensions I ever had wast in an Alfa Romeo, an IRS setup called DeDeon, with inboard brakes close to the differential to keep unsprung weight down. As I see many guys think of these cars as dragsters, I do not. I'll take a car that can handle high speed road courses any day. Just my opinion.

[CraigS]

There isn't much doubt that the IRS is a better suspension in every way. Yes, the 3 link can ride reasonably well, but, in the end, IRS w/ WAY less unsprung weight, will be better. And it's not just the ride, IRS is much better at handling bumps in mid corner. Both Camaro and Mustang have finally gone to IRS. There is a reason that a car manufacturer spends more money for one setup vs a cheaper one. It works better. The FFR IRS can be made to perform very well but needs some upgrades to the rubber bushings and stronger axles. This is normal for a system that was designed for grandma to drive on w/ 6 inch wide wheels and tires. For the upper limits of the performance envelope, it also needs a redesigned UCA. See a couple of threads on the coupe forum for examples. At this level the IRS is even more expensive than it normally is.

[dallas_]

Jazzman,
Not to further confuse the issue, but you should at least look into Gordon Levy's 5 link setup. He's in Arizona too if that helps.
John

[skullandbones]

There isn't much doubt that the IRS is a better suspension in every way. Yes, the 3 link can ride reasonably well, but, in the end, IRS w/ WAY less unsprung weight, will be better. And it's not just the ride, IRS is much better at handling bumps in mid corner. Both Camaro and Mustang have finally gone to IRS. There is a reason that a car manufacturer spends more money for one setup vs a cheaper one. It works better. The FFR IRS can be made to perform very well but needs some upgrades to the rubber bushings and stronger axles. This is normal for a system that was designed for grandma to drive on w/ 6 inch wide wheels and tires. For the upper limits of the performance envelope, it also needs a redesigned UCA. See a couple of threads on the coupe forum for examples. At this level the IRS is even more expensive than it normally is.

Can't let that statement fly, Craig: "IRS is a better suspension in every way". It just isn't in every way. It has an adjustment point that works when you set it up and after that it is pretty much static. In other words, you won't be able to adjust it to changing conditions. You can change the ride height a little to raise or lower the roll center but that's it for on the fly adjustment. That's why many are saying the three link is more of a performance component. There are adjustable versions that can be changed pretty easily to fit varying track and road conditions. The five links mentioned are even more adjustable. The jag, corvette, thunderbird, etc IRSs are pretty but they don't allow for that kind of adjustability on the fly. I would never contest the IRS comfort ride level, at least, for the ones I've ridden in. Also, they do track well as some buddies have demonstrated. But adjustability is not their strong point. WEK.

[Mesa Mike]

How do you plan to drive the car MOST OF THE TIME. I have IRS that handles great on and off the track. I spend much more time OFF track. IRS

[Gumball]

Since we're into that murky water of personal preference, I just wanted to go on record saying that I prefer blondes.

[carlewms]

I agree with Gumball

[CraigS]

Skull see here
http://www.fortesparts.com/factory-f...s-adjuster-kit

[skullandbones]

Skull see here
http://www.fortesparts.com/factory-f...s-adjuster-kit

I hadn't seen those control arms. Nice. Actually, I meant something different than alignment adjustment. I was referring to adjusting the geometry. I don't think the IRS is as adjustable as other types in that sense. I have heard that it suffers from the roll center being a little high. But that is not keeping it from being very trackable. I will bow out from any sort of argument about the matter. I just like for the facts to be laid out so everybody can see the options. I plan to do a lot of experimentation with my friend Mike as he tracks his IRS MKI and I would love to see how his and my 5 link compare in the twisties. We haven't gotten a chance to actually do a side by side yet. That will come. Thanks, WEK.

[rich grsc]

Since we're into that murky water of personal preference, I just wanted to go on record saying that I prefer blondes.

Sorry you are 100% WRONG, brunets, 5'6"-8", petite.

[Avalanche325]

As I see many guys think of these cars as dragsters, I do not. I'll take a car that can handle high speed road courses any day. Just my opinion.

I will agree that overall in the automotive industry, "IRS is better" is a true statement. It generally provides a more comfortable ride AND better performance, with the exception of drag racing. That being said, we are not talking about the general automotive industry, we are talking about Factory Five Racing Roadsters. So in a specific case, a general statement may or may not be true. So it doesn't matter what works better in a different car. It matters what works in this one.

Who would know? Probably Factory Five themselves. As stated before, I made two separate calls and had in depth conversations with two different people. Here are the results:

Comfort = IRS
Track day / road course = 3 - link
Autocross = 3- link
Drag Racing - I didn't mention it.

The SECOND I said track, they said "You want the 3-link". When I said autocross, they reiterated "3-link". I questioned them, basically saying, "Really, IRS doesn't handle better?". The reply was "The IRS is the comfort suspension. If you are putting the car on the track at all, you definitely want the 3-link."

To back that up. When they have to race an Original IRS equipped Cobra, including an autocross, they brought a 3-link. When they were racing a Lamborghini on a road course, they brought a 3-link.

I'm not making this stuff up........

[lcarpen]

Some good information from owners that have used both on track. This forum is very technical as well. I took away that the IRS is superior.

From my experience tracking a sn95 with a solid axle and panhard, the rear end movement is uncomfortably vague when going through corners. Just my 2c.

http://corner-carvers.com/forums/showthread.php?t=30647

[Jazzman]

Thank you to edwardb and dallas. I met yesterday with Gordon at his shop. We discussed in depth the benefits of the various types of rear suspension. I learned far more than I could take in, but I did decide to go with the Levy 5 Link setup. I was impressed with his explanation of how it all worked, and the cost is significantly less than an IRS setup. I think it will do what I want to do.

[aspbite]

Who would know? Probably Factory Five themselves. As stated before, I made two separate calls and had in depth conversations with two different people. Here are the results:

Comfort = IRS
Track day / road course = 3 - link
Autocross = 3- link
Drag Racing - I didn't mention it.

The SECOND I said track, they said "You want the 3-link". When I said autocross, they reiterated "3-link". I questioned them, basically saying, "Really, IRS doesn't handle better?". The reply was "The IRS is the comfort suspension. If you are putting the car on the track at all, you definitely want the 3-link."

To back that up. When they have to race an Original IRS equipped Cobra, including an autocross, they brought a 3-link. When they were racing a Lamborghini on a road course, they brought a 3-link.

I'm not making this stuff up........

When I ordered my roadster from FFR I did ask which rear suspension would be best for Drag racing and holeshots with sticky tires. I was told the 4 link as they felt the IRS and 3 link were not up to that amount of stress on a regular basis. I decided on the levy 5 link as well.

[dallas_]

I learned far more than I could take in, but I did decide to go with the Levy 5 Link setup.

I think you will be really pleased with it.

[Gumball]

Sorry you are 100% WRONG, brunets, 5'6"-8", petite.

Now we're back to the comfort versus performance argument.