The Roadster Shop has introduced a new chassis platform designed specifically for Fox Body Mustangs. Unlike partial kits that only address the front or rear, this setup provides a complete bolt-on solution. It was created with street performance in mind, giving builders a solid foundation that improves stance, suspension geometry, and overall drivability without requiring major body modifications.
This chassis integrates directly with factory mounting points and supports a wide range of engine and transmission options. It also allows for larger tire fitment, improved exhaust routing, and upgraded rear suspension components. The result is a system that balances modern performance with straightforward installation.
Key Takeaways
- The chassis offers a complete bolt-on platform for Fox Body Mustangs
- It improves stance, suspension geometry, and tire fitment
- It supports multiple engine, transmission, and exhaust setups
Overview of the Roadster Shop Spec Chassis
The Roadster Shop introduced its Spec Chassis for Fox Body Mustangs at SEMA 2024. This is a full bolt-on platform designed to replace the shortcomings of the factory setup. Unlike partial front or rear kits, it provides a complete solution aimed at street performance builds.
Key design goals included:
- Achieving the correct stance and wheel fitment
- Supporting a wide range of tire sizes
- Offering compatibility with multiple engine and transmission options
- Providing bolt-on installation without major body modifications
The chassis lowers the car about 7 inches, with the front slightly lower than the rear. This drop closes the factory wheel gap and allows for up to a 255 front tire and 285 rear tire in stock tubs. With a mini-tub, it can handle up to a 345 rear tire.
Front suspension highlights:
- Upper and lower tubular control arms
- RS-forged aluminum knuckles compatible with Corvette hubs
- Power rack-and-pinion steering
- Heavy-duty sway bar
Engine compatibility includes:
- Small Block Ford (factory location)
- Coyote
- Godzilla
- LS and LT platforms
Most engines and transmissions fit under the stock hood and tunnel. Larger transmissions may need minor clearance work, but no full modifications.
Exhaust routing features:
- Designed for 3-inch exhaust front to back
- OEM-style hanger provisions at multiple points
- Clearance for routing over the rear axle with a notched 9-inch housing
- Exhaust tucked above the frame rails for a clean side profile
Rear suspension setup:
- Four-link with full-length panhard bar
- Strange 9-inch rear axle
- Track width options: 61 inches standard or 56 inches for mini-tub applications
This platform provides a complete bolt-on chassis tailored for Fox Body owners who want a solid foundation for street-focused performance builds.
Design and Engineering Highlights
Custom-Built Foundation
The chassis was developed as a complete solution for Fox Body Mustangs, replacing the lack of a full-frame option in the market. Engineers focused on achieving the correct stance first, setting the ride height about 7 inches from the ground with a slightly lower front. This setup allows for 25-inch front tires and 26-inch rear tires, while closing the fender gap by around 2 inches compared to stock. With a mini-tub kit, the platform supports rear tires up to 345mm wide.
Key suspension features include:
- RS forged knuckles made from 6000-series aluminum
- Compatibility with modern Corvette hubs
- Tubular upper and lower control arms
- Heavy-duty sway bar
- Rack-and-pinion steering
Intended Users
The platform was designed for street performance enthusiasts rather than every type of builder. It suits drivers who want a capable street car, whether they also own a drag setup, a notchback, or are building a project in their garage. The design addresses the shortcomings of the original Fox Body by combining stance, tire clearance, and suspension geometry into one integrated system.
Simple Fitment Process
The chassis uses a 100% bolt-in design, attaching to the same factory points as the original K-member. This approach eliminates the need for major body modifications.
Engine compatibility:
| Engine Type | Fitment Notes |
|---|---|
| Small Block Ford | Mounts in stock location; factory headers often reusable |
| Coyote | Fits under stock hood; proven steering clearance |
| Godzilla | Fits under stock hood in most cases |
| LS / LT | Supported with full transmission clearance |
Additional installation details:
- Most transmissions, including large 10-speeds, fit with minimal adjustments
- Designed for 3-inch exhaust routing from front to rear
- OEM-style exhaust hanger provisions built into the frame
- Notched 9-inch housing allows exhaust to pass cleanly over the rear axle
The rear suspension uses a four-link setup with a panhard bar, paired with a heavy-duty 9-inch rear end. Track width options include 61 inches standard or 56 inches for mini-tubbed cars running wider tires.
Optimized Stance and Tire Fitment
Proper Ride Level
The chassis sets the car at about 7 inches from the ground to the pinch weld, with the front sitting slightly lower. This drop lowers the fender line by about 2 inches, closing the gap seen on stock Fox Body cars. The setup supports a 25-inch overall diameter front tire and a 26-inch rear tire, giving the car a balanced and functional stance.
Front and Rear Tire Measurements
Up front, the design allows a 255-width tire, which is the largest size recommended while still keeping full steering clearance. A common fit is a 255/40-17 that works without rubbing issues.
In the rear, the standard chassis accepts up to a 285-width tire within the stock wheel well. With the stance lowered, the rear fender gap also closes by about 2 inches, giving a cleaner look while keeping proper clearance.
| Location | Max Tire Width | Example Fitment | Notes |
|---|---|---|---|
| Front | 255 | 255/40-17 | Full lock-to-lock steering |
| Rear (stock well) | 285 | 285/40-17 | Max without modifications |
Wider Fitment with Mini Tub
For those adding a mini tub, the chassis supports much larger tires. With this modification, the rear can handle up to a 345-width tire. A common setup shown is a 335/35-17 paired with fan blade wheels.
| Rear Setup | Max Tire Width | Example Fitment |
|---|---|---|
| Stock Well | 285 | 285/40-17 |
| Mini Tub | 345 | 335/35-17 |
Chassis Integration and Suspension
Front Subframe and Attachment Points
The factory front K-member comes out, and the new chassis bolts directly into the same original locations. This setup keeps installation straightforward while improving strength and geometry. The design also provides clearance for multiple engine options, including Coyote, Godzilla, small-block Ford, LS, and LT platforms. Most combinations fit under the stock hood and transmission tunnel without major modifications.
Key features include:
- Direct bolt-in using factory points
- Compatible with multiple engine and transmission setups
- Proofed steering linkage with rack-and-pinion integration
- Provisions for 3-inch exhaust routing with OEM-style hangers
Camber Control and Cornering Setup
The suspension geometry places the upper control arm slightly lower and farther back. This adjustment helps generate negative camber during cornering, keeping the tire flat against the pavement. The result is better grip and a more predictable contact patch under load.
Benefits of this layout:
- Improved negative camber gain
- Stable tire contact during spirited driving
- Reduced compromise between comfort and handling
RS Forged Steering Knuckles
The chassis uses forged aluminum knuckles built from 6000-series material. These parts are both lightweight and stronger than stock components. They also accept modern Corvette hubs, giving builders access to updated hardware and improved serviceability.
Highlights:
- Forged 6000-series aluminum construction
- Lower weight with added strength
- Direct compatibility with Corvette hub assemblies
Engine and Transmission Compatibility
Engine Options Supported
The chassis accepts multiple engine families, including Coyote, Godzilla, Small Block Ford, LS, and LT. All of these engines fit under the stock hood line in naturally aspirated form. Supercharged setups may require additional clearance, depending on the unit used.
Transmission Clearance
Most transmission choices fit inside the tunnel with no cutting. Even large units, like a 10-speed automatic, only need minor adjustments at a few small spots. No major modifications are required, making installation straightforward.
Fitment Notes:
- Nearly all engine and transmission pairings clear the tunnel.
- Minor clearance work may be needed only with the largest gearboxes.
- Exhaust routing is already proven for 3-inch systems, with hanger points built into the frame.
Small Block Ford Placement
The Small Block Ford sits in the same position as the original factory setup. This allows existing components, such as headers, to be reused without changes. By keeping the stock location, owners can transfer parts directly from their old setup to the new chassis with minimal effort.
Exhaust System Solutions
Header and Pipe Routing
The chassis design allows room for multiple engine choices, and the header fitment has already been tested for proper clearance. Steering linkage passes cleanly through the driver-side header using a double D shaft and two joints, which keeps installation straightforward. Each header setup for the Coyote engines follows the same layout, ensuring consistent fitment.
Factory-Style Mounting Points
Several hanger locations are built into the frame so the exhaust can be mounted in a way that mirrors factory-style support. These points include:
- Transmission crossmember
- Ahead of the rear muffler
- In front of the rear axle housing
- Behind the fuel tank
This layout keeps the system stable and easy to service.
3-Inch System Fitment
The frame is shaped to carry a full 3-inch exhaust from the headers to the rear of the car. A notch in the 9-inch housing creates space for the pipes to pass over the axle without contact during suspension travel. The system tucks tightly under the floor, staying hidden above the frame rails so nothing hangs below the body line. This packaging keeps ground clearance intact while allowing a larger-diameter setup.
Rear Suspension and Differential Upgrades
Four-Bar Rear Link System
The chassis uses a four-bar rear link design that improves stability and handling compared to the stock setup. This layout helps manage traction while keeping the suspension geometry consistent under load. It also provides better articulation for both street and performance use.
Lateral Control Bar Setup
A full-length lateral control bar works with the four-link system to keep the rear axle centered. This reduces side-to-side movement and helps the car track straight. The design also supports predictable handling during cornering and acceleration.
Heavy-Duty 9-Inch Housing
Instead of the factory 8.8 rear, the chassis comes with a Strange 9-inch differential. This upgrade offers greater strength and durability for higher power levels. The housing is also notched in the center to allow a full 3-inch exhaust to pass over it without clearance issues.
Width Choices for Rear Track
Two track width options are available:
| Track Width | Wheel Mount to Wheel Mount | Tire Fitment Potential |
|---|---|---|
| 61 in. | Standard width | Works with factory wheel wells |
| 56 in. | Narrowed width | Allows wider tires with a mini-tub (up to 335–345) |
These choices let builders match the chassis to their preferred tire size and body modifications.
