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

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.

This is the IRS installed in the Mk4 Roadster.

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

The new IRS was track tested in the Mk4 Roadster.

First 2015 IRS installed in a Factory Five Mk4 Roadster.

CAD file of new 2015 Factory Five IRS.

CAD file of new 2015 Factory Five IRS.

CAD file of new 2015 Factory Five IRS.

’33 Hot Rod chassis with new 2015 IRS.

’33 Hot Rod chassis with new 2015 IRS.

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

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.


The new 2015 Factory Five Independent Rear Suspension takes its rightful place as the premium Factory Five suspension option.  It supersedes 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