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Stop the Hop: Why Upgrading the IRS is the Best Bang for the Buck S550 Mustang Upgrade

When Ford introduced the brand new S550 Mustang platform for the 2105 model year it was a huge leap from the Mustangs that came before it for many reasons, chief of which was a move from a solid axle to an independent rear suspension setup. For the vast majority of enthusiasts this was a welcome and long overdue move, as a car with IRS will typically handle better, ride better and be more predictable than a solid axle.

2016 Ford Mustang GT White

There would, however, be some drawbacks to the new setup, especially for those who were interested in raw acceleration and track performance. Hard launches and low speed acceleration in high powered car with IRS don’t just lead to wheelspin, but to wheel hop as well.

S550 Mustang Nitto NT555 G2

I experienced this first hand in my own 2016 Mustang GT when I took it to the drag strip earlier this year. With traction control disabled, I had to be very careful not to overdo it off the line and on a few of my runs I could immediately feel the distinct sensation of the rear wheels jumping about, briefly losing their contact with the ground.

S550 Mustang GT Drag Racing

This wasn’t unexpected of course, and it’s been one of the most common complaints when it comes to the S550 Mustang platform. Fortunately, the aftermarket has stepped up with a number of solutions to this problem, and during the recent mechanical makeover of my Mustang I installed Steeda’s IRS Ultimate 'Stop the Hop' packages.

Steeda's IRS Stop the Hop Package

As the name implies, this package bundles together a handful of Steeda components aimed at drastically reducing the S550’s wheelhop, limiting rear subframe movement and improving both acceleration and control.

Steeda S550 Mustang IRS Upgrades

The package includes a few important parts, first up a Subframe Bushing Support System that helps reinforce the relatively soft factory bushings in the S550’s rear subframe, eliminating flex and movement.

Steeda S550 Subframe Bushing Support System

There’s also a set of Adjustable Rear Toe Links that not only allow for easy adjustment of rear toe (especially on lowered cars like mine or cars that see track use) but they are also stiffer and more secure than the factory pieces, helping to keep the rear end planted and much more predictable.

Steeda S550 Adjustable Toe Links

The package also includes one of Steeda’s most popular S550 parts, Billet Aluminum Vertical Links —a stronger, stiffer replacement for the factory links that keep the rear suspension geometry in check and wheel carriers from hopping around during hard driving.

Steeda actually offers two different versions of these—one with Delrin bushings for drag use and one with polyurethane bushings for street, road racing and autocross. I went with the urethane version.

Steeda S550 Mustang Billet Vertical Links

Additionally, the package includes Steeda’s IRS Subframe Support Braces, which tie together three points on the S550’s rear subframe, further eliminating both side to side and vertical movement, improving both traction and handling.

Last but not least, it also includes a Subframe Alignment Kit that helps straighten out any of the variance in the position of the rear subframe and also makes it so you can loosen the rear subframe without a needing an alignment afterwards.

S550 Mustang Steeda IRS Support Braces

Installation and Performance 

Seeing as how my S550’s rear subframe already needed to be loosened and lowered for my previously covered coilover install, all of the install for all of these new IRS parts was pretty straightforward - and even just test driving my car around the block the improvement was immediately noticeable.

Steeda S550 Mustang GT Steeda IRS Upgrade Kit

Swapping out to 295 width Nitto NT555 G2 tires in the rear had already helped to reduce wheelspin, and with my same tire setup is was clear just how much more planted rear end was.

S550 Mustang GT RTR Wheels Nitto NT555 G2 Tires

Prior to the 'Stop the Hop' kit, you’d have to be careful with throttle application coming out of corners or even just accelerating in a straight line. But now you have to be much more purposeful and aggressive if you want to spin the tires or pitch the car a little sideways.

S550 Mustang GT Autocross

This was confirmed even more when I took the car to the autocross event on the Buttonwillow kart track. While it was fun drifting around and trying to keep the car pointed straight before, the rear end was so much more secure with the new parts, easily allowing me to get on the throttle sooner, harder and with a lot more confidence than before.

S550 Mustang GT Autocross Track

I haven’t yet had the chance to go back to the drags to see how much raw acceleration and 60 foot times have improved, but I’m certainly looking forward to doing that soon.

All things considered, this package might just the best bang for the buck upgrade one can do to an S550, because it addresses one of the key weaknesses of the stock S550 and you make virtually no sacrifice in comfort or noise.

S550 Mustang GT Lowered

For a relatively small investment you’ll have an immediate and noticeable improvement even on an otherwise bone stock car. Rather than adding power to your car, it's usually better to first make sure it's already getting the most out of what it has—and that's exactly where these parts Steeda have demonstrated.

Stay tuned for more progress on my Mustang project coming soon.

  • Faster, Cooler, Better: Bolt-On Upgrading the S550 Mustang GT for Street & Track Supremacy
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