Mustang IRS vs. 3-Link

[aarvig]

Ordered my FFR MK4 with the new mustang IRS but at 3k for the overall price difference between the two I'm not sure I want to keep it as an option. I'm building my car for street performance/cruising only but need to keep it under budget. My question is this:
Is the new IRS really worth the 3k difference?

[Jeff Kleiner]

"Worth it" is going to be subjective. For years FFR referred to the 3 link as the performance configuration and the T-bird derived IRS as the comfort suspension. I don't think there is enough real word experience out there yet to determine where the '15 Mustang type IRS fits into the matrix. While the IRS will undoubtedly provide a better ride on poor surfaces the 3 link ride quality is not poor. I'm happy with 3 link and if I were building another for myself there's a 95% chance I'd do it again. Not much of an answer for you I guess but only you can determine if the $3K step up is a budget buster.

Jeff

[edwardb]

Yea, what Jeff said. :) For years, Factory Five has said the 3-link = performance option, IRS = comfort option. With the new design 2015 Mustang based IRS, they are saying it's the performance and comfort option. Track testing has apparently demonstrated it's as good or better than the 3-link setup based on track times. This wasn't the case before. For street performance/cruising, probably this isn't too important though. I've had two solid axle cars and I don't consider the ride "bad." It's a stiff race car like suspension, and rides exactly how I would expect it to ride. I haven't ridden in or driven an IRS version, but working on one now. I'm looking forward to what it's like. I expect it to be good. Is it worth the extra $$$? Hard to say. I think it's a personal choice. It may have some impact on resale value, but hard to say on that too. My other comment is that many aspects of these builds can be changed after receipt or further down the road once you've driven it a while, etc. But this isn't one of those choices. Don't do something you will regret later. That isn't meant to try to sway one way or the other.

One aside comment that I find interesting. In a thread a while back, there was some discussion about why the IRS is the comfort ride. While the IRS configuration no doubt has something to do with it, it was explained by FF tech that IRS has softer springs. Because the driveshafts in these cars is so short, it's necessary to keep the solid axle movement more limited than IRS with the fixed location center section. I'm far from an expert on this subject, but this makes sense to me.

Good luck with your choice and upcoming build.

[Garry Bopp]

Just a few comments ... does the 3 link come with the axle/differential? If you have to buy that separately, then the cost differential will be less than $3k. Though we don't ever contemplate selling our cars, the IRS will bring a higher resale value.

Good luck on your build and post lots of pics!

Garry

[aarvig]

No, the cost differential is about 3k. The total cost of the IRS package is just south of 5k with center section, axles, spindles, sway bars and IRS compatible rear brakes. So when you figure the cost of the axle for a 3-link plus the standard rear brakes the difference is 3k.

[ram_g]

First off, I agree with your last statement. Having recently priced out a possible 2nd FFR Kit, the new IRS package is eye-popping in cost, almost 25% of the rest of it.

I don't have personal experience with either the new or old IRS, but I wanted to chime in to add another vote to the effect that the 3-link ride is not bad. I further improved how my car feels by going to 15" wheels rather than the 17" that I started with - the additional side wall compliance gives a definite improvement to the ride. Since I don't track the car I don't worry about side wall flex.

[BEAR-AvHistory]

My 72 year old wife was surprised how well the 3 link rode & was quite happy riding in the car. Rear is an anvil tuff simple construction that will stand up to any abuse you want to throw at it. Take the $3K & put it into other good stuff.

[edwardb]

No, the cost differential is about 3k. The total cost of the IRS package is just south of 5k with center section, axles, spindles, sway bars and IRS compatible rear brakes. So when you figure the cost of the axle for a 3-link plus the standard rear brakes the difference is 3k.

Having thought about this a little more plus reading this response, a quick follow-up. Your number is probably about right, although it might be closer to $2500 if you compare apples to apples. First, I'm pretty sure the sway bar option isn't required for street driving. Whether adding it to IRS or 3-link, it's a wash. The brakes too are going to be close to a wash. The 2015 Mustang center section, knuckles and hubs are available for around $1500 brand new in the box from Ford Racing. That's for the non-Torsen variety. New take outs (what I have) are slightly less if you can find them. That's what FF was offering the last I knew, but don't have current info. If you buy a ready to use 8.8 solid axle (again, apples to apples) from the usual sources (Forte, Moser, etc.) it's going to be more than that. The 2015 IRS center section is bigger and beefier (aka "Super 8.8" by Ford) and is 34 splines at the diff, 32 splines at the hub. 8.8 solid axles are usually 28 spline, although 31 spline upgrades are available. Is the extra beef required for your intended use? Probably not, but nice to know it's there. There are other options to get an 8.8 axle ready to go for much less, and guys do. But typically means starting with a donor, rebuilding, etc. Nothing wrong with that and certainly up to the task. Just depends on what you want to do.

[Duke]

Ordered my FFR MK4 with the new mustang IRS but at 3k for the overall price difference between the two I'm not sure I want to keep it as an option. I'm building my car for street performance/cruising only but need to keep it under budget. My question is this:
Is the new IRS really worth the 3k difference?

The 3-Link is a very solid platform. Is the IRS overall better, yes. Is it 3K better? Depends on your needs. For what you stated you are doing with it, probably not (especially considering the budget impact if you are on a budget). The 3 link rides very well on the street and it's very predictable on the track.

[aks801]

Not to sidetrack, but my understanding the IRS option as-is is designed for 17" or larger wheels. I will be using 15's. Has anyone yet built out the new IRS with 15" wheels?

[edwardb]

Not to sidetrack, but my understanding the IRS option as-is is designed for 17" or larger wheels. I will be using 15's. Has anyone yet built out the new IRS with 15" wheels?

Officially, yes. 17 or 18 inch wheels are the recommended sizes for the new 2015 Mustang IRS option. This is partly driven by the recommended Ford 2015 Mustang brakes or the optional Wilwood upgraded brakes. I've seen several threads where guys are pursuing 15 inch wheels with this IRS. Mike Forte and Gordon Levy were mentioned, and I recall Gordon promising a Wilwood brake option with 15 inch wheels. You could check with them.

[Duke]

Not to sidetrack, but my understanding the IRS option as-is is designed for 17" or larger wheels. I will be using 15's. Has anyone yet built out the new IRS with 15" wheels?

I believe I'm the first build actively doing 2015 IRS with 15" wheels. I mocked up the wheels on a set of spindles earlier this month while at Mike's shop and they fit without issue. Both Mike and Gordon are working on a brake kit, both taking a slightly different approach. I have Gordon's old IRS kit for 15's and am patiently waiting on my back ordered spindles from FFR. Once I have them I'm shipping a spindle, brake, and wheel to Gordon so he can come up with his brackets. At current date he hasn't been able to start as he doesn't have a spindle handy.

[aks801]

I believe I'm the first build actively doing 2015 IRS with 15" wheels. I mocked up the wheels on a set of spindles earlier this month while at Mike's shop and they fit without issue. Both Mike and Gordon are working on a brake kit, both taking a slightly different approach. I have Gordon's old IRS kit for 15's and am patiently waiting on my back ordered spindles from FFR. Once I have them I'm shipping a spindle, brake, and wheel to Gordon so he can come up with his brackets. At current date he hasn't been able to start as he doesn't have a spindle handy.

There ya go! I had seen your thread but just couldn't locate it. So, it looks like the brakes are the main "custom" item. I look forward to seeing the solution that you utilize.