The answer to this question depends upon your perspective.


Maximum Performance = Solid Rear Axle
Comfort = Independent Rear Suspension

Results from the Solid Rear Axle (SRA) chassis configuration is unparalleled in performance from other designs as it allows for devices to manage longitudinal loads (TorqueArm) and lateral loads (Watts Link or Panhard Bar). 


We will continue the rear chassis debate by providing a history of each design along with their benefits below. If our short answer was sufficient for you, please make sure to read the  Front Chassis Debate




The SRA Geometry provides room for ehanced predictability of the chassis via the TorqueArm managing longitudinal forces and the Watts Link (or Panhard Bar) to manage lateral loads. 


The Independent Rear Suspension (IRS) was introduced at atime when modern construction had not created the most ideal roads. This geometry allows for independent articulation of each rear wheel, which is ideal when dealing with roads that have excessive pot holes. Additionally, it serves as a buzzword for manufacturers.


Griggs Racing S197 Solid Rear Axle with TorqueArm & Watts Link



Griggs Racing chassis systems guarantee predictable performance at the maximum limit: our TorqueArm controls longitudinal movement under heavy throttle and braking, while the Watts Link controls lateral movement and offers roll center height adjustment.  For the serious racer or performance enthusiast, do not overlook this critical detail in vehicle dynamics!

2003-2004 Cobra IRS with Non-Coil Over Shocks



This is designed with comfort in mind. Aside from bushing replacements and a coil-over conversion, there is little that can be done to increase performance or control - proving it less than ideal for racing applications.  You may think we forgot about the "IRS Bumpsteer Kit" - we will discuss that further below.


Griggs Racing TorqueArm & Spider Watts Link Center


Griggs Racing SRA System Installed on S197



Because the SRA Geometry allows for devices such as the TorqueArm and Watts Link or Panhard Bar, the rear axle can be significantly enhanced.

Names include Solid Rear Axle, Stick Axle, Live Axle, our design specifically uses...

Proven Performance
The geometry is nearly identical to that of the proven AIX National Championship-winning GR40SLA systems already on the market, with the exception of minor changes due to track, wheelbase and center of gravity differences between the S197s and earlier cars.  

Simple & Complete 
The system replaces everything in the front end from steering and spindles to K member, along with the #1 cross member or radiator cowl support.  As delivered from Ford, this heavy part is separate from the K member, but is integral in the GR40 unit, which weighs just 42 lbs. complete.  Since the integral design combines the two members, it no longer resembles a letter of the alphabet so we refer to it as the “Front Cradle”.

Light Weight, Easy Access
The complete GR40 system saves considerable weight and opens up space in the engine compartment as well, making working on the car a breeze.  Using GR40 aluminum spindles and Griggs 13.5” Sport Brake Kit, total OEM parts weight removed is 261 lbs.  Installation of the GR40 front end alone removes 30 lbs. from the front end of the car, most of it un-sprung.

The inherent design of the S197 chassis allows us to make the car be very low in appearance, maintaining the well known “Griggs Stance,” as low as 2-1/2” at the rear K member mounting plate.  The resultant low center of gravity is FAST!

Rear Weight Bias Obtainable
Our test car yielded a 50.2% rear weight bias with a full tank of fuel and 210 lb. driver.  This was a S197 GT in street trim, with battery in the stock location and all systems stock except for the GR40 chassis and brakes.  Additional modifications can be made to a car to move the wieght bias even further to the rear.

Easy Installation
All parts bolt on except for two small stiffener plates to be welded to the rear shock mounts on the rear axle and, in front, four 7/16” holes drilled to facilitate installation. 

Benefits Over IRS

  • Available for street and racing applications
  • Race winning performance, suitable for Daily Drivers
  • Substantially increased rear grip
  • Incredible accuracy and feel
  • More effective braking
  • Much improved rear tire wear


Wider Tires can be used to further increase your rear tire contact patch without having to replace your factory fenders, it is possible to fit tire widths up to 315mm!

Griggs Racing GRV Shocks (5in, 6in & 7in)


Enhanced Damping

  • Improves Traction and Lateral G’s. 
  • Can be used on any high performance vehicle with appropriate mountings and adaptors.
  • Designed the rigors of performance driving GR40 Mustangs during any use of the car including street. 
  • Performance Criteria Developed and track tested by Bruce Griggs for real world road racing.
  • Aluminum Billet construction.
  • Extremely easy hand adjustable compression and rebound with positive lock positioning. 
  • You don’t need to be an engineer to use and adjust.
  • Adjust for track firmness or street comfort with no tools required.
  • Wide adjustment range facilitates easy optimization to current track and tire conditions. 
  • Digressive compression curves for best track performance yet smooth when adjusted for the street. 
  • Linear rebound curves to reduce potential traction loss due to “Jackdown.” 
  • Low pressure gas filled, yet thermally stable. Tested in grueling conditions.
  • Price point is between Koni 30 series and Koni 3012 series.
  • Teflon lined spherical bearing ½” ID mounts preloaded for long rattle free life.
  • Adjustable spring seats have a detent every 1/16 inch of spring height adjustment to ease chassis setup. 
  • Fully Serviceable
  • Made in USA


Additional Benefits for Track Drivers

  • Significantly better lap times
  • Substantially increased front grip and response
  • Improved turn in, reducing entry and mid-corner understeer
  • Back to back testing on 2.5 mile road course between the best strut systems we offer and SLA resulted in over a 2 second improvement with Toyo 275/40-17 RA1s and 3.1 seconds with 315-30-18 Hoosier R6s
  • Better braking due to less static camber requirement and improved anti-dive geometry and minimal track change during dive
  • Minimal roll center migration stabilizes chassis balance but maintaining consistent weight transfer as body pitches and rolls. This minimizes steering corrections required

Additional Benefits for Mechanics

  • Easy alignment and chassis set up
  • Quick removal of spring and shocks affords ease of bumps steer adjustment 
  • Placement of upper ball joint permits wider wheels than other SLA systems
  • Aggressive Camber pattern greatly improves front tire life, and temperature balance resulting in no more shoulders worn to belt with half tread remaining in center -  Many users tell us this pays for the system after several weekends of running
  • Utilizes existing GR40 K Member, so contact us if you are upgrading from a GR40 Strut system.
  • Utilizes low friction ball joints and Delrin bushed upper control arms for rattle free and quiet operation
  • Common shock absorber fitment. System fits any common brand 5" stroke shock with 1/2" inch ball mounts each end that is appropriately valved. Coil-over shock system for adjustable ride height and corner weight. Fully developed double adjustable aluminum bodied GRV shocks also available. 



The Independent Rear Suspension was implemented by factory production because of attention to NVH (Noise-Vibration-Harshness), prioritizing comfortability out of concern to a wide demographic appeal.  Catering to both the performance and comfort concerns, it was a grand slam that created market buzz talking about the "new and improved design", which is great for marketing material and sales.

From Wikipedia: "Independent suspension typically offers better ride quality and handling characteristics, due to lower unsprung weight and the ability of each wheel to address the road undisturbed by activities of the other wheel on the vehicle. Independent suspension requires additional engineering effort and expense in development versus a beam or live axle arrangement. A very complex IRS solution can also result in higher manufacturing costs."


2003-2004 Cobra with Stock IRS


2003-2004 Cobra IRS


Independent Rear Notes

  • Prioritizes comfort over performance
  • Better suited for non-competitive applications

How We Improve IRS Systems

  • Converting to coil-over shocks & springs
  • Using Double Adjustable shocks (mandatory)
  • Replace all bushings with low friction compound
  • IRS Bumpsteer Kit


Select one of the options below, our Virtual Consultant will guide you step-by-step to your ideal chassis system.

Our Virtual Consultant presents a guided experience, only showing items compatible with your choices.







Additional information, articles and documentation we have to offer pertaining to this vehicle