Day 17 of 20: All-New 2015 Factory Five Independent Rear Suspension

[Dave Smith]

The new Factory Five Indepentdent Rear Suspension is designed to use 2015 and later Ford Mustang center section, spindles, and brakes. The new IRS is available for the Mk4 Roadster, '33 Hot Rod, and Type 65 Coupe. The suspension is available with new kit orders, and is priced at $2,499.

2015 donor Mustang parts can be used currently. Ford Motor Company will be supplying Factory Five with all-new Mustang centers, spindles, and brakes in the near future, and we will be selling these factory-new parts at an attractive price. This suspension option can be ordered now with '33 Hot Rods, Mk4 Roadsters, and Type 65 Coupes. We will continue manufacturing the gen 1 T-Bird-based IRS for existing kit orders and for replacement parts. We have also developed with our partners at Wilwood optional Wilwood brakes. These have track and street tested, and will be standard on the 20th Anniversary car. They will be an available option soon.

Parts included:
- Welded tubular steel IRS frame
- Upper and lower control arms with bushings, grease fittings, and fasteners, powdercoated gloss black
- Left and right IRS toe adjustment arms with rod ends and fasteners, powdercoated gloss black
- KONI coil-over shocks with coil-over kit, springs, and fasteners
- Right and left CV axles
- Rear wheel studs
- IRS e-brake cable adapter
- Differential mounting components, bushings, and fasteners
- Driveshaft adapter for manual cast iron center section

Note: Requires 2015 Ford Mustang manual transmission center section, spindles, and brakes. Aluminum center sections from automatic transmission Mustangs are not useable.

Click here to see the packlist of all parts included in the new suspension. (http://www.factoryfive.com/wp-content/uploads/2015/06/ffr-irs-packlist.pdf)

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The Factory Five 2015 IRS was tested/proven in the ’33 Hot Rod chassis.

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The new IRS was track tested in the Mk4 Roadster.

http://www.factoryfive.com/wp-content/uploads/2015/06/new2015Ford-IRS-2.jpg
First 2015 IRS installed in a Factory Five Mk4 Roadster.

http://www.factoryfive.com/wp-content/uploads/2015/06/IRS-Assembly.jpg
CAD file of new 2015 Factory Five IRS.

http://www.factoryfive.com/wp-content/uploads/2015/06/IRS-Assembly2.jpg
CAD file of new 2015 Factory Five IRS.

http://www.factoryfive.com/wp-content/uploads/2015/06/IRS-Assembly3.jpg
CAD file of new 2015 Factory Five IRS.

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’33 Hot Rod chassis with new 2015 IRS.

[Dave Smith]

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’33 Hot Rod chassis with new 2015 IRS.

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The 2015 Factory Five IRS is standard in the 20th Anniversary Special Edition Mk4 Roadster.

The new 2015 Factory Five Independent Rear Suspension takes its rightful place as the premium Factory Five suspension option. It superceeds the previous gen IRS that was engineered in 2000. We will continue supplying replacement parts for the gen 1 T-Bird-based IRS.

This new suspension delivers the softest and most compliant ride, and yet, was track qualified at NCCAR where Factory Five National Champion John George reported that the new suspension was faster on a track than the proven 3-link rear suspension which is standard in the Challenge Series cars and a popular option for Roadster, Coupe, and Hot Rod customers.

Factory Five Racing

[jceckard]

Is that a RoadRunner peeking out of the hood in that last picture?

[68GT500MAN]

What a great addition to the FFR line!
Doug

[dagall]

Now a retrofit kit needs to be made to go into existing 33's. That would be a great addition to our cars.

[jayguy]

Is there any fore-aft adjustability with the IRS on the HotRod? Quite a few people have wanted to move the rear end back about an inch to center the wheels in the fenders better, will this be available or is it designed to sit the wheels in the same place as the earlier suspensions? (3 and 4-link)

[Dave Smith]

Jay - The IRS in the Hot Rod (not this way in the Roadster or 65 Coupe) is actually 1/2" further back (aft) which effectively increases the wheelbase by that much. The challenge with the Hot Rod is that the fender radius is not a circle, rather more tear drop shaped. The larger the diameter of the tire, the more this discrepancy between the tire OD and the fender line. By moving the suspension rearward by a 1/2", the look is more centered.

http://www.factoryfive.com/wp-content/uploads/2015/06/IMG-20150610-00943.jpg
This is my '33 Hot Rod with the new IRS installed and 20" rear FFR Bonneville wheels (the wheels are in stock!).

As far as retro-fitting into existing cars, we knew this question was going to come up, but the tooling issues are fairly complex and at least for now, we will not be able to accommodate retro-fits.

[Vman7]

Now this is Totally Awesome!!!!! :):) Great job FFR!

[progmgr1]

Dave - you guys nailed it again! For the last year I've been trying to figure out how to add an IRS to the '33 - tracking Ira's BMW M3 IRS adaptation, talking to outside vendors, etc. It looks like you've resolved a whole lot of issues for me in one swell foop! I am curious about one thing: is there a clear path to route rear exhaust pipes past the IRS in the modified '33 chassis? Either way, this IRS is a great enhancement to the '33 Hot Rod package. Congratulations on another job well done!
Keith

[Dave Smith]

Keith, You brought up one of the other items that we had to address with the new IRS, namely the rear exit exhaust. The current IRS, 4-link and 3-link all accomodate the side or rear exit exhaust on the 33 Hot Rod. With the new IRS, there is less room and the geometry, control arms, and frame supports make the current rear exit exhaust not fit. The answer is simply to re-design the rear exit portions of the polished ss exhaust. On my 33 the exhaust dead ends after the mufflers under the car for that reason. We are tooling up for new rear exit exhausts so those will not be an issue. likely lead time on that is a few to 3 months for prototype, tooling, first article approval, and production parts. We decided to release the IRS without that item completed as the side exits work fine and the re-tooled rears will be within 3 months. I'm very excited to show the new IRS off tonight at Patriot Place cruise-in on my Mk4 Anniversarry car and this weekend at the 2015 Open House event. We'll have updated photos from these.

[Jeff Kleiner]

Really looking forward to checking this out "in the flesh" at the Open House this weekend! As cool as it is for the roadster this is massively huge for the Hot Rod and has made my enthusiasm for the '33 take a significant step upwards :)

Jeff

[Mad Dog]

Jeff - the guys have tested the new Wilwood brakes that have been made to fit with this IRS as well. These parts will be available in the next week or so.

http://www.factoryfive.com/wp-content/uploads/2015/06/55A1549.jpg
This is the IRS installed in the Mk4 Roadster.

http://www.factoryfive.com/wp-content/uploads/2015/06/55A1498.jpg
Optional Wilwood brakes have been made to accomodate the 2015 Mustang rear suspension.

Above: Wilwood rears, Below: Wilwood fronts. These cool parts will be available shortly.

http://www.factoryfive.com/wp-content/uploads/2015/06/55A1542.jpg

[myjones]

Jay - The IRS in the Hot Rod (not this way in the Roadster or 65 Coupe) is actually 1/2" further back (aft) which effectively increases the wheelbase by that much. The challenge with the Hot Rod is that the fender radius is not a circle, rather more tear drop shaped. The larger the diameter of the tire, the more this discrepancy between the tire OD and the fender line. By moving the suspension rearward by a 1/2", the look is more centered.

http://www.factoryfive.com/wp-content/uploads/2015/06/IMG-20150610-00943.jpg
This is my '33 Hot Rod with the new IRS installed and 20" rear FFR Bonneville wheels (the wheels are in stock!).

As far as retro-fitting into existing cars, we knew this question was going to come up, but the tooling issues are fairly complex and at least for now, we will not be able to accommodate retro-fits.

Dave
What's the ride height on your car in this picture?
Is it an illusion from those wheels or is it a bit higher?
BTW love the IRS and twin sway bar options for the 33.
Dale
Hemi33

[jayguy]

Thanks Dave, the new updates to the HR kit look great! Can't wait to get my hands on one.

Jay

[Plebeian]

Any idea what the power limitations are on this set up?

[David Hodgkins]

Any idea what the power limitations are on this set up?

I don't have a direct answer for you but I just talked with Jim at FFR about it. To put in perspective the design parameters: The original pumpkin was designed around the 220 HP 5 liter in the ~ 1990 Thunderbird. And the new "Super 8.8" is designed to handle the various Coyote motors in the new mustang platform.

:)

[Jester]

Can the new IRS be retrofitted into a completed MK4 (3 link)? How much welding is required?. I would consider upgrading my 15th anniversary Mk4 to the new IRS & brake package. Can this be purchased as an upgrade for completed cars? Great addition to the roadster!

20th anniversary version is wicked! - need a new garage to build another one!

Thx

[Oppenheimer]

What is the performance expectation with the new IRS? Is the new IRS expected to out perform the other options now (3 link, 5 link) on a road course or canyon?

[jayguy]

This new suspension delivers the softest and most compliant ride, and yet, was track qualified at NCCAR where Factory Five National Champion John George reported that the new suspension was faster on a track than the proven 3-link rear suspension which is standard in the Challenge Series cars and a popular option for Roadster, Coupe, and Hot Rod customers.

Factory Five Racing
Dave Smith, FFR 001
President
Factory Five Racing

Yes, from post 2, Dave answered that question.

[Oppenheimer]

Thanks. I did read that. I guess was looking for more detail. How much faster? And was it faster by happy coincidence, or was the goal at the outset for this to out perform all the other options (FFR supplied or otherwise)? (or was it more about 80's T-bird pumpkins are getting harder to come by, etc?)

I guess we will know more once people have built cars with this option, and people who have driven various examples of the other options can weigh in. But there are obviously already people who have tested the new suspension that fit that criteria, so it would be nice to hear more about what its like. What the differences are, etc.