2015 IRS Ride...

[aarvig]

I am wondering if anyone has any non-biased ride reviews for the 2015 IRS suspension? I am also wondering if sway bars are required for that set-up? I bit the bullet and ordered my MK4 kit with the IRS but on the off chance there is not a significant improvement over a live axle, I am going to switch back to the live axle to save some dough. My purpose for the car is street cruising/performance so comfort is a concern...
Thanks guys! Looking forward to beginning an exciting family build project.

[edwardb]

I don't think there are many completed 2015 IRS builds out there yet. They were just starting to be delivered in July/August. In fact the only one I can think of might be the Ohio Cobra Club's 001 Anniversary edition that was just completed for their annual London Cobra Show raffle. I've seen pictures of the build on Facebook, and I'm pretty sure I saw where they're taking it to car shows now. So maybe someone in that club has an opinion since it's probably been driven? Other than that, it's going to be a while. I hope to have mine ready for go-kart later this year when it turns warmer. But even that's not a very good test. Until you really get it done and put some miles on it, hard to say. I'd be willing to bet for street cruising/performance driving, the sway bars wouldn't be required. The good news is they can be left off at the beginning, and added later pretty easily. The same can't be said for the rear suspension. Basically a one and done decision, e.g. pretty impractical (and expensive) to change solid axle car to an IRS. I would say especially so with the new IRS. The mounting bracketry is pretty unique. Have you actually ridden in one of these? Comfort is a relative term, and means different things to different people. I think it's very safe to say the IRS would be a more comfortable ride than the 3-link. That's how it's always been advertised, and that's the overwhelming feedback from customers. But how much better and is is worth it? That's an individual decision. But if comfort really is one of your primary goals, I would try to figure out how to stay with the IRS. I see you have a DART 347 listed as the planned engine. Great choice. I have one and love it. But pretty pricey. I know first hand how much they cost to build. A strategy I would suggest is to dial down the engine plans, e.g. a nice strong stock block or even Coyote (!!) and put the difference in the IRS. You can change/upgrade the engine in the future if you want to. The rear axle decision you really can't.

[2bking]

While I don't have the 2015 IRS, I can say my older style IRS was a very surprisingly nice ride. I have a two lane black-top road I use for test drives that is very bumpy and constantly in need of repairs from overloaded trash trucks. I have a Ranger pickup that catches air on some of the worst places and can pitch me around. I was worried that the cars low clearance would drag the frame on some of the bumps but that didn't happen. The roadster smoothed out the bumps and has a much softer ride than the pickup.

[aarvig]

Thanks for the advice guys. Since I live in Minnesota and our second season after winter is road construction season going with the IRS is pretty much mandated.

[Avalanche325]

I am wondering if anyone has any non-biased ride reviews for the 2015 IRS suspension?

It's still hard to find an unbiased view on the old one!

Honestly, the 3 link ride is surprisingly good. I have a friend that spent an hour in an IRS car (old version) and then an hour in my 3-link. He said he couldn't tell the difference, and he is building an IRS one. I don't know how calibrated his butt is. The new one is supposed to be all that and a bag of chips.

[CraigS]

I think you will be very happy w/ it based on my wife's 2015 Mustang GT. I call it a major improvement over her 2010 GT which had the old 3 link.

[jayguy]

Dave Smith's Roadster has the new 2015 IRS in it, and they have a '33 with it installed also (the black one with the flames). You could go to the factory and ask to drive one of those to see how the new IRS feels in an FFR. :)

[Mesa Mike]

I have one of the first IRS cars FFR build back in 2000. My car handles far better than any of my friends solid axle set ups. 3 link, 4 link 5 link or no link with the solid axle. I don't believe there is a need for a sway bar in the back but the front will benefit from one if you track it. The new set up is 500lb springs on the front and 800b on the rear. Mine came with 450b all around but I have switched the rear to 750b. 450lb was too soft and would bottom under hard cornering sometimes.

[Avalanche325]

My car handles far better than any of my friends solid axle set ups. 3 link, 4 link 5 link or no link with the solid axle.

Then why did FFR state for years that the old IRS was for comfort and the 3-link was the performance suspension? The second I mentioned autocross and possible track, they said 3-link. I called a 2nd time to be sure and got the same story from a different person. They also always used a 3-link car when they did a test or TV show where performance was key. The new one may be different. But that was the story with the old one. May yours is set up better.

[David Hodgkins]

Then why did FFR state for years that the old IRS was for comfort and the 3-link was the performance suspension? The second I mentioned autocross and possible track, they said 3-link. I called a 2nd time to be sure and got the same story from a different person. They also always used a 3-link car when they did a test or TV show where performance was key. The new one may be different. But that was the story with the old one. May yours is set up better.

For hard core racing the 3link is better than the old IRS. It holds up to the rigors of racing better. I don't know what FFR's position on the new IRS will be for hard core track use.

:)

[johngeorge]

Im adding 2015 IRS to FFR#48 and will be stress testing it on track all next year :)

[Hotyacht]

I shake my head on this topic...........I have no means of comparing the options in these roadsters, but when I ordered my kit and chose to run with IRS, I simply asked myself..........How many performance car manufacturers out there build cars with a solid rear axle? Couldn't think of a single Ferrari, Lamborghini, Porsche, lotus, Aston, Mercedes? And how many race cars are there without IRS - I mean cars that have to go around corners in both directions? What did the original 427 Cobras have? Seemed like a pretty simple choice to me.

[JNC]

I'm quite sure that all the performance cars that you've mentioned have IRS systems designed specifically for performance sports cars. The old IRS style stuff that F5's made use of was found in mild performance luxury coupes, so the choice wasn't so simple, for the racers anyway, prior to the 2015 stang stuff.

My $0.02...



I shake my head on this topic...........I have no means of comparing the options in these roadsters, but when I ordered my kit and chose to run with IRS, I simply asked myself..........How many performance car manufacturers out there build cars with a solid rear axle? Couldn't think of a single Ferrari, Lamborghini, Porsche, lotus, Aston, Mercedes? And how many race cars are there without IRS - I mean cars that have to go around corners in both directions? What did the original 427 Cobras have? Seemed like a pretty simple choice to me.

[Hotyacht]

Only the centre section and half shafts are from the T-Bird......the control arms, coil overs etc i.e. the moving parts, are specific to the FFR Roadster. Solid axles pretty much went out of fashion with the Roman chariot

[edwardb]

Only the centre section and half shafts are from the T-Bird......the control arms, coil overs etc i.e. the moving parts, are specific to the FFR Roadster.

Actually it's the center section and knuckles/hubs that are used from the T-Bird. Same as the new 2015 Mustang setup. Factory Five supplies everything else with the IRS option including the CV axles (half shafts). I guess early on you had to move CV joints to new axles that FF supplied. But now they supply the complete assembly ready to go.


Solid axles pretty much went out of fashion with the Roman chariot.

Exaggerate much? I could think of just a few examples in the couple thousand years since that where a solid axle was a perfectly good solution. ;) But on a more serious note, on these cars traditionally the 3-link was the performance solution and IRS was the comfort solution. And the track times confirmed this. Maybe it was a function of the specific IRS setup, but has been the case. The new 2015 Mustang version is being sold as both. Best performance and best comfort. Again with track times to confirm. But for many, the 3-link is still completely viable and is a good value. 5-link is another excellent solid axle option, although not available directly from Factory Five.

On a separate but related note, I was reading on a Mustang enthusiasts forum the other day, and people were lamenting the decision by Ford to go 100% IRS for the Mustang starting in 2015. For some enthusiasts, their performance ideas prefer a solid axle. They were even considering the option to retrofit a new Mustang back to solid axle. Specifically they were discussing drag racing, where they have trouble with breaking axles and wheel hop. Just goes to show one persons idea of a performance setup is not the same for all.

[Avalanche325]

I have no means of comparing the options in these roadsters.....
Factory Five did the comparisons. Their conclusion was that the 3-link was better for performance. I am sure the new IRS is vastly improved, and may indeed be the ultimate suspension for these.

I am sure the old IRS was intended to be a better performer. It just didn't work out that way when the rubber met the road, so to speak. It is not the first, or hundredth, time a suspension design didn't work quite as intended. The first generation Audi TT IRS got enough people killed to have a global recall. Then there were swing axles, an early IRS system that put more than a few cars belly side up.


Couldn't think of a single Ferrari, Lamborghini, Porsche, lotus, Aston, Mercedes? And how many race cars are there without IRS - I mean cars that have to go around corners in both directions? What did the original 427 Cobras have? Seemed like a pretty simple choice to me.

I agree that you would THINK that IRS was a no-brainer. But research shows different results. What Ferrari, Lamborghini, Porsche, lotus, Aston, Mercedes uses has absolutely nothing to do with an FFR. What an original Cobra had really doesn't either. A 3-link FFR (which FFR chose to use over an IRS car) was run against an original Cobra. Watch this and see which car you want yours to handle like.
http://www.powerblocktv.com/episode/MC2012-05/427-cobra-and-factory-five-roadster

Here is what they rolled out against a Lamborghini. Dave Smiths 3-link, and Summit Racing's 3-link.
https://www.youtube.com/watch?v=V96-AQ1FghI

I am not saying this because I bought a 3-link. I bought a 3-link because of what FFR said and what real proof showed. If I were doing one today, with what I know so far, I would do the new IRS.

[Hotyacht]

Thanks for the links, they are interesting but I don't see that they prove anything here? Looked to be more about brakes shocks and tires to me - not to mention drivers. Anyway I am very comfortable with my choice and I think it is fantastic that there are so many options with these cars.

On a less serious note - As far as people lamenting the IRS on the new Mustang.............I guess it took a while for people to get over the world not being flat too. Drag racing! What is it with that stuff? Sorry I'm an F1 fan, but then there are plenty of people who cant see why I sit and watch cars zooming around in circles for 2hrs either.

[Avalanche325]

Thanks for the links, they are interesting but I don't see that they prove anything here?
The point that I was trying to make is that when FFR had to bring out their "big gun", it was a 3-link every single time. They wouldn't bring their 2nd best to the fight. But, whatever, that suspension is gone now anyway. I am interested to see how the new one performs.

F1 fan here too!

[cgundermann]

Curious to see how the new IRS does on the track; similar discussion to the recent carb vs. EFI debate. Setup is everything...

I have an old school EFI 347 and a 3-link. When the 03/04 Mustang "Terminator" Cobra came out, many rear ends were swapped for solid axle. The new Stang's IRS with strong half shafts should do really well in the high horsepower range. I also like F1 and the curves - evolution...

[bcovell]

I have a MKII with IRS and added adjustable sway bars (Vintage) front and rear. Car rides very well on the street and handles terrific on the track... 2015 IRS should be the same

[Avalanche325]

It's still hard to find an unbiased view on the old one!

Honestly, the 3 link ride is surprisingly good. I have a friend that spent an hour in an IRS car (old version) and then an hour in my 3-link. He said he couldn't tell the difference, and he is building an IRS one. I don't know how calibrated his butt is. The new one is supposed to be all that and a bag of chips.

I wanted to do an update on this for honesty sake. I rode in his car and mine. The IRS does ride smoother, to my calibrated rump. I beat him by 1.7 seconds on a 42 - 44 second autocross course.

[David Hodgkins]

For hard core racing the 3link is better than the old IRS. It holds up to the rigors of racing better. I don't know what FFR's position on the new IRS will be for hard core track use.

:)

I thought I'd update this comment since this thread is back TTT. John George (about as close to a FFR Factory driver as you can get if your name isn't Jim Schenk) just posted that he has - with the help of FFR - upgraded his challenge racer to the 2015 Mustang IRS setup:
http://thefactoryfiveforum.com/showthread.php?20017-2015-IRS-install-in-FFR-48

I think that goes a long way in stating FFR's position on the performance parameters of the new setup.

:)

[j.miller]

I'll throw my hat in the ring. The most comfortable ride was or is IRS 450lbs springs 50 series 15"s on the back. If you went to 17" on the back you loose the sidewall and you are back to a stiffer ride so you may as well have gone 3link and save the clams. There is something to be said for saying "I have IRS". With 450 springs these cars have way to much body roll for performance driving so if that's what you want then go to 650-750 springs.....if you do that the ride stiffens up so 3link would have saved the bucks once again. Yes, many cars come with IRS and these cars were designed from the start with IRS and are specificly set up to work with chassis design (to the best of my knowledge they are all unibody with chassis flex. Also, allows for smaller drive shaft tunnel. As far as racing, race teams have a war chest of shocks and springs to be able to tune a chassis to the track they are running and that's not reality for us....so, it comes down to "what you want most of the time out of your car" you can't have it all all the time but you can have most of it most of the time..........just like everything else in life. Remember' my thoughts are worth no more then you paid for them.................and that's all I have to say about that...da Bat