Christopher Campbell Technical Editor
November 7, 2013
The Watt’s-link pivot uses a Delrin bushing on its mount for controlled movement with zero deflection. Notice the double-shear arrangement on the center pivot bolt. This adds significant strength and plenty of safety factor to the design. All critical points of the Xtreme Grip kit have a torque spec, but pay special attention to the Watt’s-link differential-cover pivot-bolt spec since it needs tightening, but not too much.
Using the factory diagonal brace bolts, install the Watt’s tower bracket to the driver-side framerail in the location of the original brace bolt holes. Although not necessary, this bracket can be welded in for the ultimate in strength and rigidity.
Begin with the Watt’s link at the lengths delivered and adjust them if needed to center the axle. The new diagonal brace bolts into place afterward. The ability to choose from a number of center pivot hole heights is key to tuning the handling of the rear suspension. The higher holes stiffen the rear suspension, and the lower holes soften it allowing adjustment of grip to get a neutral-handling car. CorteX suggests starting in one of the middle holes.
Since this is the street kit, polyurethane bushings are used at the outer attachment points of the Watt’s links for NVH control. The inner attachments at the pivot are Heims for precise movement. The diagonal brace (right) is length-adjustable on the driver side for possible minor adjustment, ensuring fit regardless of tolerance stack-up or production tolerances. The passenger side is a solid mount.
The last piece installed for our Street kit is the original 19mm antiroll bar and its factory endlinks. It’s perfect for dual-duty street/track cars, but more aggressive cars can opt for upgrades per CorteX’s recommendations.
To ensure the rearend housing is centered, choose a reference point that is common on both sides and measure to the brake rotor. If the rotors are used as a reference point, make sure to fully install two lug nuts on each side to ensure the brake rotor is flush with the axle hub. Adjust the Watt’s links as necessary to center the axle to within 1⁄16-inch.
Compared to the rear, the front portion of the Xtreme Grip kit is a super-quick process. First remove the wheels and unbolt the strut from the spindle.
Since we’ll be installing CorteX’s caster/camber plates, the factory upper strut mount is removed via the bolts on top of the strut tower.
Like the rear coilovers, the fronts are custom-valved, single-adjustable Koni Sport and are shipped assembled with the caster/camber plates from CorteX. For the Street kit, the Eibach springs are 400-450 in-lb depending on the model of Mustang (GT vs. GT500). The really cool part of these coilover struts is the offset that allows 10.5-inch wheels with 315 tires with zero clearance issues!
The one upgrade we added to our base Xtreme Grip street kit is the optional Eibach front antiroll bar. This CorteX-spec bar is three-position adjustable and specifically suited for use with the Xtreme-Grip kit.
We also opted for CorteX’s adjustable endlink. This link allows the preload to be taken off the bar while corner-weighting the vehicle. Constructed of high-strength aluminum, and fitted with stainless-steel misalignment bushings, it also makes slight adjustments to the front bar possible. Note we started with the endlinks in the middle mount hole on the Eibach bar.
With everything bolted together and all torque specs rechecked front and rear, we dropped the Mustang down and set the alignment with a Longacre kit. We went with 7 degrees of caster, -2.5 degrees of camber, and a 0-degree toe angle.
Look at that meat! We can fit a 10.5-inch CorteX CX14 wheel with 315/30 Nitto NT-01 rubber on all four corners now, while still maintaining a factory turning radius!
Here’s a peak at how much clearance the relocated CorteX coilover offers while still improving the front suspension geometry. You simply can’t do this with most coilover kits.
If you’re looking for an affordable way to get that much wheel and tire on your car after the Xtreme Grip makeover, CorteX also offers these custom-spec, one-piece Jongbloed (www.jongbloed Series 700 wheels designed for perfect fitment with the Xtreme Grip kit.

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Virtual Ride

Check out CorteX Racing's Youtube channel ( for an amazing in-car HD video of a CorteX equipped Spec Mustang attacking Laguna Seca. It may be hard to believe, but the car in this video is mechanically identical to our test car other than long-tube headers, an X-pipe, full Heim joints on the Xtreme Grip system, and a gutted interior—that's it! So yes, you can have this level of grip in a daily drivable S197! Turn up the sound loud for this one!

The ride isn't as intense, but also check out the video of our test car getting its suspension installed and then tested on Sonoma Raceway there as well!

Stock Cortex Suspension
Maximum Lateral Acceleration, left, Turn 3 1.107g 1.305g
Maximum Lateral Acceleration, right, Turn 7 1.096g 1.284g
Average Lateral Acceleration 1.102g 1.294g
Maximum Apex Speed, Turn 6 69.76 mph 72.89 mph
Best Lap Time 02:05.1 01:58.0

We documented our results with a datalogger, and as you can see, the lateral grip increased by 17.4 percent with the Cortex suspension, and lap times dropped by 7.06 seconds per lap.

Horse Sense: If the Cortex gear interests you but you don't own an '05-and-up Mustang, don't fret. The company also offers parts and complete suspension systems for '79-'93 and '94-'04 Mustangs.