We took our new 2024 Mustang GT to Steeda in Georgia to have their Stop the Hop Street Starter kit and Linear Drag springs installed before we hit the track. Not because the car was slow. Because we have learned this lesson the expensive way twice.
Like the S550 before it, and the 03-04 SVT Cobra before that, the 2024 S650's independent rear is prone to wheel hop. That leads to broken axles and poor traction, which are the two things a drag racer least wants. There are hundreds of suspension parts aimed at this. For most people starting out, the Stop the Hop starter kit is the right first move.
What Wheel Hop Actually Is
Wheel hop is the rear tires hopping up and down rapidly under hard acceleration. It happens because the car is rapidly gaining and losing traction as the suspension binds and then releases, over and over, several times a second.
On an IRS car it is usually not the tire or the shock. It is the entire rear subframe deflecting, which is why it feels like a hard shudder through the whole back of the car rather than something happening at one corner.
The root cause is a deliberate factory decision. The 2015-up Mustang IRS uses soft rubber bushings, and those bushings are genuinely good at what Ford wanted: excellent ride quality, very low NVH, civilised street manners. They are also, by the same property, an open invitation to deflection under load.
The Starter Kit's Three Parts
Steeda's Stop the Hop Starter Kit bundles three components. Each one addresses a separate source of movement, which is why the kit works better than any of them alone.
Subframe bushing support system
IRS subframe support braces
No permanent modifications
1. Subframe Alignment Kit
From the factory, the bolt holes for the rear subframe bolts are considerably larger than the bolts themselves. Think hot dog in a hallway. Those gaps mean your rear subframe can sit out of alignment by up to half an inch.
Steeda's answer is CNC-machined Delrin sleeves that insert into the factory bolt holes. The bolts then pass through the sleeves, which fill the gap and square the subframe to the chassis. Same alignment every time, no guesswork.
2. Subframe Bushing Support System
You could replace the factory bushings outright. That is labour intensive and it usually brings high NVH, more gear whine, and more noise in general. Steeda took a different route: the support system envelops the factory bushings and fills the factory voids, eliminating the movement without removing the rubber that keeps the car civil.
It is a 10-piece kit, CNC-machined from billet 6061 aluminum, and it was the first of its kind on the market for the S550 and S650.
3. IRS Subframe Support Braces
Made in-house from 4130 chrome moly with a silver powdercoat. These triangulate the subframe to the chassis by connecting three points: existing threaded holes in the rocker panel, which is the strongest part of the body, the front mounting location of the IRS subframe, and the rear mount of the lower control arm and toe link.
Tying those three together adds rigidity the rear of the car never had, and Steeda's point is that it gives you more control of the whole car rather than just the rear end. 50% more connecting points, all factory bolt locations, no drilling, and no cradle removal to install.
Squares subframe to chassis
No increase in NVH
Limited lifetime warranty
Supports the factory bushings
Increases traction, no added NVH
First of its kind for S550 / S650
Triangulates 3 chassis points
50% more connecting points
No drilling, no cradle removal
Linear Drag Springs
Traction is half the equation. Weight transfer is the other half, and that is what the Linear Drag springs are for. They were designed with the drag racer in mind, with rates chosen for the best weight transfer and most traction on a launch, while still keeping the car genuinely street driveable.
| Spec | Front | Rear |
|---|---|---|
| Drop | Roughly 1" | Roughly 0.75" |
| Spring rate | 150 lb/in | 800 lb/in |
The soft front and stiff rear is the point, not a compromise. A soft front lets the nose rise and transfer weight rearward on the hit; a stiff rear resists squat so that weight actually loads the tires instead of collapsing the suspension.
150 lb/in front, 800 lb/in rear
Street driveable
Lifetime warranty
Do not use the standard springs
Same drag-focused rate philosophy
The Full Kit Ladder
The starter kit is the entry point, not the ceiling. Steeda builds a whole ladder above it, and which one you want depends on whether you are chasing straight-line traction or corner grip.
| Kit | Part number | Aimed at |
|---|---|---|
| Starter Kit | - | Everyone. Alignment, bushing support, braces |
| Street Enthusiast | 555-4456 | Street cars wanting more than the starter |
| Drag Enthusiast | 555-4456-D | Straight-line focus |
| Street Ultimate | 555-2129 | Full street build |
| Drag Ultimate | 555-2129-D | Full drag build |
| Handling Ultimate | 555-2129-H | Road course and canyon |
| Ultimate Street / Handling, 2024+ Brembo | 555-2129-7GPP / -H-7GPP | S650 with Brembo brakes |
Street-focused
Straight-line focus
Handling and Street Ultimate also available
One more thing worth doing while you are back there: the differential bolts. Factory hardware has enough play to let the diff move, which changes pinion angle and breaks axles. We wrote that one up separately in the Extreme Differential Bolt Upgrade.
Huge thanks to Steeda for bringing us up to Georgia to get this installed on our 2024 GT.
Frequently Asked Questions
What causes wheel hop on a Mustang?
The rear subframe deflecting under load. The 2015-up IRS uses soft rubber bushings chosen for ride quality and low NVH, and that softness allows the movement that becomes wheel hop.
Can wheel hop break parts?
Yes. We have broken axles at the track on a bone stock 2018 Mustang GT and on our 2020 Shelby GT500, both from wheel hop off the line.
Do I need power before wheel hop is a problem?
No. One of the cars we broke was completely stock. Traction and suspension deflection are separate from how much power you make.
What is in the Steeda Stop the Hop Starter Kit?
Three components: the IRS subframe alignment kit, the subframe bushing support system, and the IRS subframe support braces.
Will the Stop the Hop kit add NVH or make my car loud?
No. All three starter kit components are specifically designed not to increase NVH, because they support the factory bushings rather than replacing them with solid mounts.
How far out of alignment is a factory Mustang subframe?
Up to half an inch. The factory bolt holes are much larger than the bolts, so the subframe can sit off centre. The alignment kit's Delrin sleeves fill that gap.
Does installing this require permanent modification?
No. Every part uses factory bolt locations, nothing needs drilling, and the braces install without removing the cradle.
Which drag springs do I need if my car has MagneRide?
The 555-8233 MagneRide-specific springs. The standard 555-8231 is not correct for MagneRide-equipped cars.
Should I buy a bigger Stop the Hop kit instead of the starter?
Only after the starter kit content is in place. The alignment kit and bushing support are the foundation. Adding links and arms to a misaligned subframe wastes them.
Keep Reading
Stop Breaking Axles
Alignment, bushing support and braces. Reversible, no added NVH, and the foundation for everything else you do back there.
