1955-1959 GM Truck Extreme IRS Chassis

1955-1959 GM Truck Extreme IRS Chassis

Speedtech Performance

SKU
71232IRS-T
$33,902.96
Estimated Shipping Date: Sep 17, 2026
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California Prop 65

The Speedtech ExtReme Chassis with Independent Rear Suspension is engineered to elevate the performance of 1955–1959 GM trucks — delivering a lowered stance, increased tire capacity, exceptional chassis rigidity, and modern handling capability for both street and performance driving.

Built on proprietary suspension geometry and paired with QA1 or JRi coilovers, this system is further refined with a precision dual-power rack and pinion from Sweet Mfg., providing responsive, connected steering feel with a smooth, controlled ride. Forged aluminum spindles and optimized front-end geometry allow for aggressive alignment settings and clearance for wide front tire fitment, ensuring these classic trucks handle with confidence and precision.

At the rear, the Independent Rear Suspension introduces superior compliance, strength, and adjustability—maximizing traction, improving ride quality, and delivering consistent performance across a wide range of driving conditions.

Extreme Subframe - 55-59 Gm Truck

AGGRESSIVE STANCE, WIDE TIRE FITMENT 

Designed with wide wheel and tire combos in mind, this subframe accommodates up to a 315/30/18 tire with full steering clearance. High-clearance control arms and optimized geometry let you slam the car for that strong pro-touring look without compromising performance or drivability. 

PRECISION STEERING FEEL, DUAL RACK PERFORMANCE 

At the heart of this system is a dual power rack and pinion from Sweet Mfg., giving you a quicker ratio and improved feedback for confident cornering. Combined with our billet steering arm and ExtReme spindle geometry, you’ll feel in full control at every turn. 

RACE-BRED STRENGTH, STREET-READY RELIABILITY 

Box-welded construction with tabbed-through gusseting maximizes torsional rigidity, while our 7075 forged aluminum spindles bring lightweight strength to the front end. It’s engineered to take abuse—on and off the track. 

extreme IRS 55-59 Gm Truck

INDEPENDENT REAR SUSPENSION

Speedtech Performance’s ExtReme IRS system is not just an upgrade; it's a complete transformation of your classic car's handling capabilities. By incorporating advanced suspension technology, it delivers a modern driving experience while preserving the timeless appeal of your vintage vehicle.

MADE IN THE USA WITH PRIDE 

Every Speedtech subframe is built right here in the USA, using premium materials and expert craftsmanship. We believe in building it right the first time—with no compromises. 

INSTALLATION MADE EASY, NO GUESSWORK 

The ExtReme Chassis bolts directly to the stock location, making installation straightforward for builders, pros, or advanced DIYers. To achieve the proper driveline angle, floor and tunnel modification will need to be done. However, Speedtech offers a full transmission tunnel, driveline and axle tunnel kit. This teamed up with our IRS closeout sheet metal, all of the material is ready for you!

Tech Info

  • ExtReme Chassis Install

 

FREQUENTLY ASKED QUESTIONS (FAQ’s)

IS A SPEEDTECH CHASSIS SUITABLE FOR BOTH STREET AND TRACK USE?

Absolutely. The ExtReme chassis with Torque Arm or IRS Rear Suspension is track-tested and customer-proven for street driving, autocross, and full track days. Its geometry, ride quality, and strength make it equally at home on Main Street or the road course.

WHAT SIZE TIRES CAN I RUN WITH THE SPEEDTECH EXTREME FULL CHASSIS WITH IRS?

This chassis is built for serious rubber—up to 315/30/18 tires in the front with full steering clearance, and up to 355/30/18 tires in the rear with the IRS setup.

WHAT ENGINES AND TRANSMISSIONS WILL FIT THIS CHASSIS?

The modular engine mounting system supports GM: LS, LT, SBC, BBC, Ford: SB, BB, Coyote and Mopar: SB, BB, Gen 3 Hemi. It’s designed to integrate seamlessly with a wide range of transmissions when paired with compatible crossmembers. (Note Pontiac engines may not fit)

WHAT MAKES SPEEDTECH’S IRS DIFFERENT FROM OTHERS?

It’s fully adjustable for camber, caster, and toe, so you can fine-tune handling, ride quality, and tire wear for street, autocross, or track.

WHAT’S ALL INCLUDED WITH THIS CHASSIS?

  • Complete ExtReme Chassis Modular Transmission Crossmember
  • Front Upper and Lower Control Arms
  • Forged Spindles with C7 Hubs
  • Steering Arms
  • Front Three Piece Sway Bar and Linkage
  • Engine Stands
  • Coilovers (if option chosen)
  • Sweet Mfg. Steering Rack
  • Rear Upper and Lower Control Arms
  • Forged Spindles with C7 Hubs (Rear)
  • Steering Arms and Tie Rods
  • Rear Three Piece Sway Bar and Linkage
  • Aluminum 9” Housing and Stub Axles (IRS)
  • CV Axles (IRS)
  • Center Section
  • Applicable Hardware
  • Billet Rockers (High Mount Rocker)
  • Billet Frame Mounts (High Mount Rocker)
  • Push Rods (High Mount Rocker)
  • Upper Shock Mount (Traditional)

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