BUY NOW, PAY LATER. Starting at 0% APR 
For the hardcore drag racer, the quest for the perfect "hook" begins and ends with the wheel and tire setup. On the drag strip, sidewall is king. More sidewall means more wrinkle, more surface area, and more traction when the light turns green. Traditionally, the gold standard for late-model Mustangs has been the 15-inch wheel conversion.
But the 2024+ S650 Mustang GT has changed the game. If you are looking to shave tenths off your ET and dial in your 60-foot times, you need to know if a 15-inch wheel conversion is even possible: or if it is the right move for your new S650.
At DTX Performance, we specialize in pushing modern muscle to the limit. Before you start ordering parts, let’s break down the technical reality of the S650 platform and what it takes to dominate the drag strip.
The Pursuit of the 15-Inch Setup
Why do racers obsess over 15-inch wheels? It’s simple: physics. A smaller wheel diameter allows for a taller tire sidewall while maintaining a manageable overall diameter. That extra rubber acts as a secondary suspension component, absorbing the initial shock of a high-RPM launch and "wrinkling" to provide a massive contact patch.
For the previous S550 generation, a 15-inch conversion was a rite of passage for serious builds. It required specialized rear brake kits, modified control arms, and occasionally some clearancing on the knuckles. However, the S650 Mustang GT presents a new set of challenges that every owner needs to understand before reaching for the grinder.
The S650 Brake Problem: Why 15-Inch Wheels Aren't Plug-and-Play
The S650 Mustang GT is a masterpiece of engineering, but that engineering includes significantly larger braking systems than its predecessors. Most S650 GT models, especially those equipped with the Performance Pack, feature massive 4-piston rear calipers and 14-inch rotors.
The Reality Check: A 15-inch wheel physically cannot clear the standard S650 GT rear brake assembly.
Unlike the S550, where aftermarket companies like Baer Brakes developed specific "deep-drop" 15-inch conversion kits, the S650 platform is still in its infancy regarding small-diameter wheel compatibility. The electronic parking brake (EPB) integrated into the rear calipers adds another layer of complexity. Removing or downsizing these components to fit a 15-inch wheel isn't just a bolt-on affair; it involves re-engineering the braking logic and safety systems of a very advanced vehicle.
17-Inch Wheels: The S650 Drag Racing Sweet Spot
If you are looking for maximum performance without compromising the integrity of your brand-new S650, the 17-inch wheel is the current "Gold Standard."
A 17x10 or 17x10.5 rear wheel provides plenty of room for a high-performance drag radial, such as the Mickey Thompson ET Street R, while clearing the factory 4-piston Brembo or performance brakes. This setup offers a significant increase in sidewall over the stock 19 or 20-inch wheels without requiring you to hack up your suspension or delete your parking brake.
Shop with Confidence: Weld Racing and Forgestar
When selecting wheels for your S650, you need brands that understand the offset and clearance requirements of the new S650 chassis. We highly recommend:
- Weld Racing: The Weld RT-S series is the industry standard. Their forged construction is incredibly light and strong. A Weld S71 or S77 in a 17-inch fitment provides the classic drag look with modern performance.
- Forgestar: For those looking for a balance of style and weight, the Forgestar F14 Drag Pack is a top-tier choice. They offer specific S650 fitments that ensure the wheel sits flush with the fender while clearing the massive rear calipers.
Select your vehicle to find the exact wheel offsets required for your S650 Mustang GT.
Suspension Modifications for the Drag Strip
Tires are only half the battle. To truly take advantage of a drag-specific wheel setup on your S650, you must address the rear suspension. Even with a 17-inch wheel and a sticky radial, "wheel hop" can destroy your 60-foot times and, eventually, your half-shafts.
To build a launch-ready S650, consider these essential upgrades:
- Vertical Links: Replace the factory rubber-bushed links with CNC-machined aluminum versions to eliminate deflection.
- Cradle Bushing Lockout Kit: This is a must. It stabilizes the rear subframe, ensuring that all the power goes to the ground instead of shaking the chassis.
- Adjustable Rear Shocks: Tuning your compression and rebound is critical to planting the tires and maintaining traction throughout the gear changes.
Explore our suspension and handling components to find the parts needed to stabilize your S650’s rear end.
Weight Reduction: Every Ounce Counts
Switching to a dedicated drag wheel setup isn't just about traction; it’s about reducing rotating mass. A factory S650 19-inch wheel and tire combo can weigh upwards of 60 lbs. A lightweight 17-inch Weld or Forgestar setup can shave 15-20 lbs per corner.
Reducing rotating mass allows the engine to spin the tires up to speed faster, effectively increasing your "at-the-wheels" horsepower. When you combine this with a lightweight front skinny wheel (18x5), the performance gains are undeniable.
Can You Force a 15-Inch Wheel to Fit?
Technically, anything is possible with enough fabrication. However, for 99% of S650 owners, the answer is "not yet." To fit a 15-inch wheel, you would likely need:
- A complete rear brake downsize (losing significant stopping power).
- Potential modifications to the rear knuckles.
- Custom-engineered brackets to retain the electronic parking brake.
For a dedicated track car that lives on a trailer, this might eventually become a viable path as the aftermarket catches up. For a street-driven GT or a weekend warrior, the 17-inch setup is the superior choice for reliability, safety, and ease of installation.
Shop performance brakes to see why keeping your factory stopping power is a smart move for high-speed runs.
Building Your S650 Drag Setup: Step-by-Step
If you’re ready to stop spinning and start winning, here is the DTX Performance recommended path for the S650 Mustang GT:
- Select Your Rear Wheels: Choose a 17x10 wheel from Weld or Forgestar with the correct S650-specific offset.
- Choose Your Rubber: Pair those wheels with a 305/45R17 drag radial for the perfect balance of height and width.
- Upgrade the Fronts: Don’t stop at the rear. A set of 18x5 "skinnies" on the front reduces rolling resistance and weight.
- Lock Down the Suspension: Install a lockout kit and vertical links to ensure a smooth, straight launch.
- Monitor Your Progress: Use the S650’s built-in Track Apps to monitor your 0-60 and 1/4 mile times as you dial in the tire pressure.
Conclusion: Stick with 17s for Now
While the allure of the 15-inch wheel conversion remains strong in the Mustang community, the S650 GT is a different animal. The engineering required to clear the factory brakes makes a 15-inch conversion impractical for the vast majority of owners.
By opting for a high-quality 17-inch drag pack from brands like Weld or Forgestar, you get the performance you crave without the headaches of extreme fabrication. You keep your safety features, your stopping power, and your warranty intact while still being able to pull the front wheels off the ground at the track.
At DTX Performance, we are committed to providing the best parts and expertise for the modern muscle enthusiast. Whether you are building a 10-second street car or a dedicated track monster, we have the components you need to succeed.
Push your S650 to the limit. Build it right. Shop DTX Performance.
Browse our full catalog of S650 performance parts.
We promise to only send you the good things: the parts that actually make your car faster.
