IRS: how does it change the ride / handling over 3 link?

[Jester]

Calling Roadster suspension experts:

I have read a number of posts with comments on IRS vs 3link however I have not found a convincing argument for one over the other i.e. how much better the is the ride and handling of an IRS MK4 when compared against a similar car with a 3 link. Is this a subjective comparison with minimal differences or is IRS clearly better than 3 link. I have a anniversary Mk4 with most performance upgrades other than IRS. My Mk 4 handles like it on rails although the ride (suspension) is stiff and bad roads need to be avoided. Would changing to an IRS improve the stiffness and ride quality? Has anyone done a side by side comparison with 2 cars (same setup) one with IRS and one with 3 link?

Thanks for the feedback

[Avalanche325]

According to two people I spoke to at Factory Five. The IRS is the comfort suspension. The 3-link is the performance suspension. As soon as I said the words "autocross and a track day or two", they said 3-link. So, the ride is better with IRS and the performance is better with 3-link. Notice that when they take a car out for a performance test, it is a 3-link. Like the FFR vs an Original and the FFR vs Lamborghini tests. Performance and comfort don't usually go together. Softer springs could be an option if you aren't tracking the car.

Giving your location might get you a ride in a IRS car.

[edwardb]

As mentioned, IRS is considered the best riding suspension. How much better? Good question. But the reality is that while it can and has been done, switching a solid axle car to IRS is not a simple mod. There's a reason the rear suspension is specified when the chassis is built. Would require some fabrication, welding, etc. to make the swap. Not to mention some pretty expensive new parts.

These things do ride a bit stiff, which is what they're designed to do. Probably you could remove some harshness playing around the springs and shocks. Way cheaper and easier options then switching out the whole rear suspension. And you'll still probably still avoid those same bad roads.

[frankeeski]

J, the single best thing you can do to improve the ride/handling characteristics of the car, regardless of the type of rear suspension, is the springs. The FFR supplied springs suck! We found up to a 75 lbs difference in spring weight from one side to the other. This was when we first corner weighted the car. The next thing is the spring weight. For the highway and even for the track in most instances, the car is over-sprung. What's the use of having springs if they are so stiff the suspension isn't allowed to react? I am currently running Eibach springs all the way around with 425 lbs springs in the front and 250 lbs. springs in the rear. With the Eibach springs we found less than a 5 lbs difference in spring rate between sides. IRS is still going to be a more comfortable ride but the springs change on my car made a huge difference. I run a Levy 5-Link with a 3/4" front anti-sway bar but you should see the same results with a 3-link. The last thing to remember is tire pressure. Depending on the side wall height of your tires you may need to run lower tire pressure

[edwardb]

The last thing to remember is tire pressure. Depending on the side wall height of your tires you may need to run lower tire pressure

I came back to add this point, but Frank beat me to it. These cars take way lower PSI than what many are used to or expecting. Varies depending on your tires, but 22-24 PSI is normally the range for street driving. If your tires are too hard, it will make a big difference.

[CraigS]

I have driven a IRS MkIV w/ the FFR konis and ridden in a 3 link MkIII w/ the FFR Konis. IMHO the 350# rear springs FFR supplies w/ the 3 link are too stiff. 250# was the solid axle standard until the FFR Koni came on the scene. The optional 'better ride' spring from VPM w/ their Carrera coilovers was 200#. I would swap to 250s and I think you will be happy.

[chopthebass]

Frankeee, so why 425 lbs in front? Is it because there's so much weight up there?

[mcwho]

I am wondering what others are using with their FFR supplied Koni Coil overs and the IRS suspension. I'm not on the road as yet but still interested.

[frankeeski]

Frankeee, so why 425 lbs in front? Is it because there's so much weight up there?

Really two things but the simple answer is yes. My car, which is pretty heavy when compared to many others, had a tendency to porpoise (bounce up and down) badly here on the highways of SoCal. This lead me to believe the suspension was not reacting as it should. I went through all of the forum advise about checking for binding in the suspension and found none. Mark Dougherty was the one that told me to look at the springs and play with rates. Second thing is, I have a front anti-sway bar. If you are going to allow the front end to actually act as a suspension you have to do something about body roll. The lighter springs allow the suspension to do it's job now and the anti-sway bar along with the adjust-ability of the 5-Link keep the body roll in check. Factory Five combats body roll with higher spring rates, I don't agree with that philosophy.

[chopthebass]

Thanks Frank. I haven't started my build yet - so info like this is really useful.
I assume the complete kit doesn't have a front anti sway bar? If that's the case and I was to build the car as supplied, would there still be a benefit using 250 rear and 425 front springs? I have 3-link, 351W 427 motor.
I know very little about car suspension so go easy on me!

[Jeff Kleiner]

... IMHO the 350# rear springs FFR supplies w/ the 3 link are too stiff...

So I guess you might not like my 500# rears.

Jeff

[rich grsc]

Jeff, you saying you have a fat a$$?

[Todd Buttrick]

I agree with Frank and Craig for a non-track car. I'm running the Carerra's @ 200# in the rear and Pro Shocks up front @ 350# w/3link and Eibock springs all around. I installed the FFR Konis on all four corners and took them off after a month. Love the ride and still out-handles most cars on the road but that wasn't my objective. Just much easier to live with and enjoy. The other BEST thing you can do is free up the suspension front and back by adding the Breeze bushings to the front lower CAs and Spohn lower control arms out back.

[Jester]

Thanks for the feedback everyone.

I really like the handling of my Mk4 and I don't mind the ride quality as this sets these cars apart but for passenger enjoyment the ride could be a little softer - my wife prefers the motorcycle over the Mk4 - something to do with the belts and ride quality not to mention too much sun (are you kidding me - sad but true). I want the car to be a comfortable as possible for the passenger however I am not sure I want to sacrifice the performance for a slightly softer ride. How much better would the ride be - is it a significant improvement with IRS (example comparisons welcome i.e. Ford 1 tone pickup vs an Infiniti G??). Would the IRS on a MK4 ride like a G? - that would be a significant improvement and I would consider changing to IRS. I set the tire pressure to around 20 lbs at the beginning of the season and that change made a significant improvement In the ride but still too stiff for some passengers. I have the upgraded Koni's and will consider changing the springs - is this something others have done - any recommendations for new springs? (I need to do more research).

It would be good to see some direct comparisons in ride characteristics between the IRS and Solid axel (with various shock spring combos).

I spoke with FFR a while back and and if my memory is correct they told me the IRS is a direct bolt in for the MK4 - no welding required.

Thanks!

[Gordon Levy]

The IRS needs to be welded in and the cost is going to be around $3500+ by the time you buy the kit from FFR, buy a donor diff and rebuild it it and set it up. Proper shock and spring set up and my lower rear control arms will help a ton. If you have the 15th anniversary edition you have DA koni's in it. I can almost guaranty that they are not adjusted correctly and a set of Eibach springs will help a lot. Feel free to give me a call if you want to talk about it.

[Avalanche325]

So I guess you might not like my 500# rears.

Jeff

His dentist might when those fillings go flying.

... had a tendency to porpoise (bounce up and down) badly here on the highways of SoCal.

Sometimes that can be just the specific wheelbase of the car and the frequency of the joints in the road. When I lived in SoCal, I had an Infiniti QX4 SUV. It would porpoise like crazy on some of the roads. I think the 405 was the worst.

[Jester]

The IRS needs to be welded in and the cost is going to be around $3500+ by the time you buy the kit from FFR, buy a donor diff and rebuild it it and set it up. Proper shock and spring set up and my lower rear control arms will help a ton. If you have the 15th anniversary edition you have DA koni's in it. I can almost guaranty that they are not adjusted correctly and a set of Eibach springs will help a lot. Feel free to give me a call if you want to talk about it.

Thanks Gordon - good to know.

Sounds like some new springs should do the trick. I will call you next week to discuss

Thx