Gallery: Speedtech Performance Expands Chassis Line with Independent Rear Suspension


Speedtech Performance has added an all-new independent rear suspension (IRS) to its B-body chassis line. Mopar Connection Magazine has had several opportunities to present Speedtech Performance’s engineering marvels. Ken Kelley’s Plymouth AAR Cuda and the Speedtech Performance Superbird are great examples of the quality of work developed at its Saint George, Utah, facility.

Above Left: Speedtech Performance has a complete chassis line for the Mopar B-bodies. The ExtReme IRS Chassis transforms a vintage muscle car’s mediocre handling characteristics to those that perform better than a late-model vehicle. Above Right: Speedtech Performance has developed an intricate sheet metal floor that is so beautiful it is almost disappointing to cover it with carpet.  

The new IRS accompanies the Speedtech Performance’s proven suspension systems, the ExtReme Front Subframe (EFSF) and Torque Arm Rear Suspension (TARS), designed for 1968-70 B-bodies. The IRS eliminates the solid axle, substantially transforming the car’s performance. Drivers of the B-bodies fitted with the ExtReme products will enjoy the benefits of comfortable long-distance drives as well as outstanding feedback through the chassis and the steering wheel.

Above Photos: The Speedtech Performance technicians carefully fit and weld the robust chassis to the former uni-bodied B-body. 

The principle behind the ExtReme Chassis products is to afford a vintage muscle car the performance and handling characteristics of a modern sports touring vehicle, which is the essence of Pro Touring.

Above Photos: The quality of the ExtReme Chassis is noticeable from every angle. The precision fit of the chassis will result in a Mopar that is comfortable on the road and predictable and responsive on the track. 

Marketing Specialist at Speedtech, Thomas LeClair, shared the following information about the car featured in the photos:

“Regarding the car featured in the images, please note that it is currently undergoing a chassis installation here (Speedtech Performance), and it will be sent back to Tom Argue Designs in Clearwater, Florida, to complete the build. The wheels in the images are temporary shop rollers with incorrect offset and backspacing. We plan to ship the car back to Tom Argue Designs on Guni Wheels, and (we) won’t get to see the car here on the perfect wheels. While the current wheels are 18 inches, we believe that using 19-inch or 20-inch wheels may further enhance the car’s overall look.

Furthermore, the tires currently installed on the car are 315 in size. However, the vehicle can accommodate larger tires while maintaining a full 30 degrees of steering angle under the stock sheet metal. We recommend considering a 325/30/19 size for the front and a 335/30/20 size for the rear. These tire options will not push the limits of what is possible under the stock body panels, providing an optimal balance between performance and aesthetics.”

Above Photos: Underneath the stock hood is a Gen 3 supercharged 6.2-liter Hemi. The ExtReme Chassis’ design locates the Hemi and matching transmission to the chassis perfectly. 

Below is a list of essential features that set Speedtech Performance’s ExtReme Chassis apart from the competition:

Unrivaled Construction: The triple-box welded construction with tabbed through frame gusseting ensures unmatched torsional rigidity, providing a solid foundation for exceptional performance.
Tailored Suspension Options: Choose between the Low Mount Shock and High Mount Cantilevered Shock IRS systems, which perfectly customize the ride.
Unleash Rear Grip: With a significantly increased rear shock motion ratio (100%), the chassis allows for lower spring rates while maintaining a superior rear grip to experience the road like never before.
Precision Adjustability: Enjoy the freedom of fully adjustable rear wheel alignment, including camber, toe, and bump-steer settings.
Next-Level Components: The ExtReme Chassis exclusively features forged 7075 Aircraft Aluminum spindles, ensuring unparalleled strength and durability.
Master the Turns: With a 325/30/19 front tire, 30 degrees of steering angle, corrected Ackerman, and optimized roll center, the chassis delivers exceptional cornering performance. Gain up to 20% more inside tire grip to conquer every curve.
Smooth and Comfortable: Experience excellent comfort on the street while maintaining durability for autocross and track days.
Complete Suspension Package: The ExtReme Chassis includes custom-designed upper and lower control arms, Sweet Mfg. dual power rack and pinion steering, JRI single adjustable coil-over shocks valved for Speedtech Performance, and a tuned, splined front sway bar. The package is meticulously crafted to ensure optimal results that match the customer’s vision.

Photos Above: During the design phase of the IRS platform, a ’68 Charger was the testbed. The 18-inch wheels were strictly “rollers” to move the Charger throughout the assembly facility. The wheels did not have the correct backspacing or offset. Speedtech Performance recommends 325/30/19 rubber for the front and a 335/30/20 out back. Although, the Charger does look good with the rollers.

Speedtech Performance expressly designs each chassis for housing a 6.2-liter supercharged Gen3 Hemi and matching transmission. To learn more about all the products at Speedtech Performance, check online or call (435) 628-4300. The expert team will guide you through the steps to transform your B-body with modern power and an innovative chassis while maintaining the original aesthetics of the muscle car era.

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Chris Holley

Technical Contributor Chris has been a college professor for 25 years; at Pennsylvania College of Technology in Williamsport, PA. for the last 20 years. Chris instructs automotive classes in HVAC, electrical/electronics, and high-performance, including using a chassis dyno, flow benches, and various machining equipment. Recently, he added a vintage vehicle upholstery class to his teaching assignments. Chris owns a '67 Dart, a '75 Dart, a '06 Charger, and a '12 Cummins turbo diesel Ram, and he is a multi-time track champion (drag racing) with his '69 340 Dart, which he has owned for 34 years.

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