SKU: 150230 Category:

ExtReme Chassis 65-70 Mustang with Independent Rear Suspension

Independent Rear Suspension (IRS) is the ultimate expression of Pro Touring to make your classic Mustang drive like a modern sport touring car. If you are not familiar with the term Pro Touring consider the following. Cars of the 60’s and 70’s were manufactured to perform well in a narrow set of circumstances. Pro Touring is defined as a classic America muscle car with enhanced capability for braking and cornering. The essence of Pro Touring is a great handling muscle car that is fun to drive on the street and is also competent on a road-course. Speedtech Performance offer our award winning IRS design for a wide range of vehicles including Ford Mustangs.

In addition to the exceptional ExtReme Mustang Chassis, we offer a comprehensive range of products meticulously crafted to enhance the efficiency of your project. Among these offerings is our cutting-edge lazer cut CNC formed sheet metal floor, ingeniously designed to incorporate components for closing in the IRS, down bars, front aprons, and much more! We pride ourselves on providing high-quality products that not only elevate the final outcome of your project but also simplify the entire process. Feel free to consult your dedicated sales representative, who will gladly enlighten you about the extensive selection of premium products available, ensuring that your project is complete and effortless.


  • Early years – 275mm wide tires with no outside fender modifications
  • Later years – 315mm wide tires with no outside fender modifications
  • Box welded construction with tabbed through frame gusseting for added torsional rigidity
  • Choice of two different IRS systems, Low Mount Shock and High Mount Cantilevered Shock
  • Significantly increased rear shock motion ratio, 100%, allows for better rear grip with lower spring rate
  • Fully adjustable rear wheel alignment – Camber, Toe, Bump-Steer
  • Exclusively equipped with forged 7075 Aircraft Aluminum ExtReme spindle (more info below)
  • Up to 30 deg of steering angle equal to or slightly more than O.E.
  • Corrected Ackerman for better grip while cornering up to 20% more inside tire grip when cornering
  • Corrected scrub radius for large diameter wheels in wider widths
  • Virtually zero bump steer – .005” standard over full travel (can be tuned)
  • Industry leading design for lower roll center optimized for each chassis
  • Excellent comfort on the street, durable for autocross & track days
  • Increased shock length providing more suspension travel
  • 78% motion ratio front for faster shock response and more precise control
  • 3-piece Chromoly tubular splined sway bar standard and a variety of spring rates available
  • Sway bar arms are 3 position adjustable for tuning without changing bar
  • Front and rear ride height adjustments accommodate your vision for styling of the finished car
  • Rear Roll Center is adjustable over based on lower control arm mounting position
  • Dutchman 9” alluminum center housing
  • Half-shaft axles using 33 spline RCV-934 C.V. Joints rated to 1200 HP (option for 1800 HP rating)
  • Removable sub frame (can be welded in)


  • 355mm wide tires with no outside fender modifications
  • Full ExtReme Chassis designed exclusively for Speedtech Performance Independent Rear Suspension
  • Custom designed upper and lower control arms with high clearance to accommodate wide wheels
  • Durable Sweet Mfg. dual power rack and pinion steering
  • JRI Speedtech Performance custom valved single adjustable coil over shocks, spring rates of your choice included
  • Tuned, adjustable, splined front sway bar with spring rate options for street, pro-touring/auto cross and road course
  • Exclusive Speedtech Performance ExtReme forged spindles with maintenance free sealed bearing
  • Fully adjustable transmission cross member that will accommodate all engine and transmission combinations
  • Billet aluminum High Mount actuating rocker arms (high mount system only)
  • Speedtech Performance exclusive ExtReme forged spindles
  • 35 Spline Inner Stub Axles
  • Outer C7 33 spline stub axles
  • 33 spline EMPI 934 CV Joints
  • Dutchman Aluminum Housing
  • Your choice of gear ratio
  • JRI single adjustable coil over shocks valved for Speedtech Performance,  JRi springs with your choice of spring rate
  • All IRS packages come standard with E Brake


  • Included with all ExtReme front suspensions and only available from Speedtech Performance
  • We took the best forged aluminum spindle made and made it better
  • Forged from high quality, light weight 7075 aerospace aluminum
  • Optimized geometry unlike in any other Corvette style spindle in the industry
  • Significantly improved KPI/SAI angle
  • Scrub radius optimized for KPI/SAI changes and larger wheels
  • Requires less caster to achieves optimum tire contact patch
  • Billet steering arm provides increased Ackerman angle
  • Achieves optimum tire slip-angles to provide increased front tire grip
  • Maintains optimum tire grip with less backspaced wheels
  • Brakes caliper bolt pattern is carryover from C5 & C6 Corvette opening up many options
  • Comes standard with maintenance free factory GM C7 Corvette hubs & bearings
  • Excellent design attributes for street cars and race cars
  • Our Spindle provides a more refined and precise driving experience in all situations


  • Frame mounted battery box
  • Coyote Engine and adapter plates as well as LS, LT, Hemi, SBC and BBC
  • Urethane engine and transmission mounts
  • Stainless steel 1 7/8″ headers for most engines
  • Stainless-Steel double joint steering shaft kit
  • Front Apron Kit
  • Floor and IRS closing panel sheet metal kit
  • Down Bars
  • Splined adjustable 3 piece rear sway bar
  • Rear end center section with your choice of final drive ratio
  • Aluminum Third Member with your choice of gears
  • Brake packages from Baer or Wilwood with or without E Brake
  • Ididit tilt steering column*
  • Stainless-Steel Rick’s fuel tank with pump options
  • Wheels and Tires
  • Bespoke PRC Aluminum cross flow radiator with twin Spal fans, shroud, billet overflow, billet rad cap all wiring and relays custom built to fit the GM Truck ExtReme frame


Note: Oil pan compatibility with chassis is specific and the pan will need to fit around the steering rack. Ask your sale person for a recommendation.

Chassis orders will be confirmed over the phone. A sales person will call you for a no cost consultation to discuss the specific details of your project and ensure you are provided with the very best customer experience.

*Factory steering columns have the incorrect length and will not work with the ExtReme suspension components. We recommend an Ididit steering column for best results. Please speak to your salesperson to order from us or to obtain the correct part number.

Note: All chassis orders will have a $900 crating fee plus truck freight shipping added on at the time of processing. These chassis can only be delivered to a shipping terminal or a business with a loading dock and/or forklift access.

Be sure to ask your sales rep about these different options to customize your frame to meet the needs of your project.