Dylan Abbott
June 7, 2016

With the redesign of the S550 Mustang came a completely new front and rear suspension; all of the existing suspension parts for the outgoing S197 platform were incompatible with the new chassis. Enter Koni, a longstanding name in the performance suspension world. Koni was quick to jump into action designing new shocks and struts for the S550 Mustangs, including the V-6, EcoBoost, and GT variants. With amazing value and an unsurpassed lifetime warranty, Koni is a great go-to option for all Mustang enthusiasts.

Koni engineers had a variety of new challenges to conquer when designing a set of shocks and struts for the S550 Mustang. With the new IRS came a new set of parameters, which meant none of the existing Koni designs would work. Koni started with its externally adjustable Sport shocks and struts and designed all-new spring perches, sway bar mounting points, rear shock brackets and bushings, and adjuster location. On older Mustangs the rear shocks typically extended into the trunk, meaning the adjuster would be inside the vehicle. On the S550 the rear shocks are mounted externally, so Koni had to ensure that its adjuster would be easily accessible from outside the car and that adjustments could be made while the shocks were installed on the car. Front adjustment is much easier, as the adjuster knob is accessible from the engine bay.

Koni also had to contend with the higher spring rates that are common to IRS vehicles. Higher rates are often needed because of the different motion ratios that come into play in comparison to solid axle Mustangs. The rear spring rates on the S550 are 600 percent stiffer or more compared to previous Mustang rear spring rates. Such high spring rates makes engineering valving that will appropriately dampen the spring motion while maintaining ride quality much more difficult. Koni chose the valving for its shocks accounting for various spring rates and tried to build something that would work well with the factory spring rates, all the way to the stiffest streetable lowering springs. Koni Sport Yellows are a great option for street performance enthusiasts that also spend some time on track.

Follow along as we install a set on a 2015 Mustang GT.

1. Lift the car, remove the wheels, and begin the strut removal by disconnecting the front sway bar endlinks. You will also have to remove the ABS sensor retainer from the stock strut.

2. Unbolt the strut from the spindle, and support the weight of the spindle to prevent damage to the brake lines.

3. Remove the three top strut mount bolts and remove the strut assembly from the car.

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4. Using a spring compressor, compress the spring, and remove the top strut nut. Keep the spring compressed and transfer the bumpstop, dust boot, spring isolator, and spring from the old strut to the Koni strut. Reinstall the top strut nut and torque to spec. Do not use an impact wrench, as it might damage the internal adjuster on the Koni struts.

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5. Reinstall the strut assembly into the car. Bolt the strut mount back in place. Reattach the endlink and ABS sensor retainer. Bolt the spindle back to the strut.

6. Moving to the rear, unbolt the shock mount from the body.

7. Unbolt the shock from the lower control arm and remove it from the car.

8. Remove the mount from the shock. The Koni shock rod is a larger diameter than stock, so you will have to drill out the mounting bracket hole to accept the Koni shock.

9. Transfer the dust boot and bumpstop from the OEM shock to the Koni. Place the supplied spacer over the bumpstop, and position the mount over the spacer. Tighten the two nuts over the mount.

10. Lastly, install the Koni shock on the vehicle and torque the bolts to spec. While this was a quick and simple install, it is one modification that will go a long way to suiting your individual needs both on the street and at the track.

All About Koni Adjustment

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Koni’s line of Sport shocks offer valving that has a 100 percent range of adjustment. This means that the shock provides roughly twice as much damping force at the maximum setting as it does at the minimum. Most other adjustable shocks do not offer such a wide range of damping settings. Spring rates and damping forces do not have a linear relationship, so doubling the spring rate on your S550 may only require a 20 to 40 percent increase in damping. Koni Sport shocks will work with a wide range of springs because of the wide range of damping adjustments.

So how does the adjustment work on the Sports? When the external adjuster knob is turned, several internal processes happen. An internal nut opens or closes bleeder valves that meter the flow of oil at low piston speeds, which in turn increases or decreases the spring preload against the shock valving. As the shock’s resistance to the work input by the spring is increased or decreased, the ride quality and handling characteristics change. The stiffer the damper settings, the more resistance to spring oscillation and a reduction in body roll.