Power Meets Control: Upgrading the S550 Mustang's Suspension with ST & Steeda

• November 30, 2020
• Story By
  Mike Garrett

Coming second only to a better set of wheels and tires, a suspension upgrade has always been one of the first modifications I’ve done to my cars.

Because when it comes to making a car look better, handle better and become more fun to drive, it’s hard to beat some quality suspension parts.  And despite being very good out of the box, my current 2016 Ford Mustang GT was no different.

Just before my car went under the knife for its upgrades, I took my Mustang to an autocross day where I pushed the car pretty hard around a tight, twisting course that is primarily designed for go karts.

Not surprisingly, I was greeted with a lot of body roll and unwanted movement in the chassis as I pushed through the car through the corners. And in higher speed cornering areas it was clear that the S550 had the bones of a great handler, but the car was softer and less planted than it should be for real enthusiast driving.

The Parts

So as one of the key upgrades of my Mustang’s “build” I spec’d out a set of ST XTA coilovers that would help make the GT lower, stiffer and a lot more confidence inspiring in the corners. (Find ST's XTA Coilovers here)

The XTA is designed to be a capable, high quality coilover setup that doesn’t break the bank. They feature adjustable ride height and sixteen stages of rebound adjustment, as well as top mounts with built-in camber adjustment.

As an added bonus, ST now offers a customization program where you can have your coilover springs painted in one of 18 different colors, plus you can choose to have words or messages printed on the spring.

For the Mustang I went with Ultramarine Blue for my spring color and represented Driving Line with my custom spring text. Think of them as “easter eggs” for your project car.

As it turns out, the blue springs would also be pretty close to the color of the Steeda sway bar kit I’d be fitting at the same time. The Steeda sway bars measure 1-3/8” in the front and 1-1/8” in the rear and can be adjusted for a softer or stiffer feel depending on your preference or use. Click here to see the Steeda Sway bars I chose)

We’d also be installing Steeda’s billet sway bar mounts in the front and rear to further eliminate flex under cornering—and yes, they also look quite cool as well. (Get the specs on the sway bar mounts here)

Lastly, we’d also be fitting one of Steeda’s Ultralite 2-Point G-Trac braces in the front, further stiffening the front subframe and eliminating flex while weighing in at just five pounds. (Click here for the details)

Easy-On

Installation was pretty straight forward, greatly aided not just by the detailed installation instructions supplied with products but also by the countless YouTube videos that show step by step how to do it. This one of the greatest benefits of today’s technology.

The biggest challenges came in removing the factory rear shocks and springs, as the S550 requires you to loosen the entire rear subframe to get them out. The sway bar install was pretty straightforward, although it did require a bit of finesse to get the front bar in and out through the chassis.

Here's the Setup

After a couple of ride height adjustments on the ST coilovers, I headed to the alignment shop where I requested a handling focused alignment recommended by fellow S550 owners for street/track use. 

Now it was time to get on the road and see how it all felt. Needless to say, the ride was stiffer than before but not stiff enough to become uncomfortable on the street - and that’s with the rebound adjustment on the coilovers still at their factory settings. The sway bars we set at one click off of the stiffest setting on both ends. 

After I took the car on a run through some of favorite local mountain roads and was immediately impressed by just how much more confidence there was in the chassis - all with the same Nitto NT555 G2 tires that I’d been running since the spring. Oh yeah, and the car looked positively mean dropped down.

Back to the Track

Better yet, I finished the install up just before another autocross day on the same Buttonwillow go kart track, where I'd just raced the car in stock form a few weeks earlier.

Because the course layout was different this time around (in fact it was even more technical than before), I couldn't directly compare my lap times, but it was amazing just how much flatter and more confident the car was around the track.

With the stock setup there was a lot of wasted time trying to keep the front and rear ends on the same page, and you had to be much more deliberate with your inputs. After the ST coilovers, Steeda sway bars and G-Trac brace the feel was much more “sports car” than before.

A small go kart track where you never get out of second or third gear was still not going to be the place for a heavy muscle car truly shine, but the new suspension parts not only made the car corner faster and flatter than it had before, I also had a much better idea of what it was going to do - allowing me to push it even harder.

The coilovers, sway bars and G-Trac brace are of course just one part of the upgrades being done to the car, but if these were results and impressions were anything to by my “build” was getting off to a great start.

Next time we'll continue with some of the upgrades done in the rear of the car to eliminate wheel hop and wheelspin and to keep the Mustang pointed in the right direction.