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2005-2014 Mustang/Shelby
Rear Chassis Systems
The Proven Innovator - not an imitator!


GR40SS Super Street System
The starter system for making a street-driven Mustang into a smooth riding Porsche killer.  The Super Street kit is configured to give you incredible hookup and significantly improved cornering performance.  It focuses on the weakest link in the S197 platform, the rear suspension.  This is a great place to start upgrades on your S197 Mustang and will give you a great foundation for future upgrades.  Major components include Koni front coil-overs, urethane bushings and the GR40ST rear suspension, including torque arm.  Installation is as easy as it gets with no welding required.  Whether you drive your Mustang to work or in the canyons this kit will yield noticable, satisfying performance improvements. 

Griggs SLA (Short-Long Arm) Systems

GR40ST Ultimate Street System
Included with the GR40ST turnkey car, the first of our S197 SLA systems includes the foundation to make a street-driven Mustang into a smooth riding Porsche killer.  It is configured to give you incredible hookup and cornering performance.  The system focuses on the weakest link in the S197 platform, the rear suspension.  Additionally, significant weight is shed from the front end, providing more neutral handling.  Major components include a tubular front cradle, Koni coil-overs, torque arm and SLA System.  Installation is as easy as it gets with no welding required.  Whether you drive your Mustang at the strip or in the twisties, this kit is guaranteed to yield significant performance improvements.  This is our most popular SLA system.

GR40TT Autocross/Open Track System
Included with the GR40TT turnkey car, the second of our S197 SLA systems is engineered for the serious Mustang driver who uses his car on the road course and still occasionally drives on the street.  The kit includes all the components of the GR40ST Ultimate Street System, but incorporates Adjustable Severe Duty Lower Control Arms, spring rate changes and Watts link.  This system will improve performance over the GR40ST system with some increase in road noise.

GR40RT Road Race/World Challenge System
Included with the GR40RT turnkey race car, this is the kit that wins it all.  THE standard of excellence.  The most popular chassis system in late-model road racing history.  Twelve years in development, it is the most dominant system on the market today.  The proof is in the race records.  If you want to be consistently fast, you need the GR40RT chassis.  If you don’t win with this, it's time to check your driving.  There is no comparison for this one.  And race parts with a lifetime warranty…really.

Rigid:  Each SLA system includes a provision for solid mounting the motor in a way that greatly increases chassis stiffness without using motor plates, which are expensive to install.  This affords the serious enthusiast nearly the same rigidity as full motor plates, but without the need to remove or even touch the engine during installation.  The rear plate is shaped to accommodate all known long tube header combinations.

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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.  

Low:  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!

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”.

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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.

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.

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BIG TIRES FIT: The unique GR40 SLA design allows us to fit 305-18 tires on 10.5” rims (standard front and rear) under stock sheet metal.  Larger sizes will fit.

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. 

Incredible Feel, Input & Response:  The first impression of all drivers that have tested this chassis is the car drives and feels like it weighs half of its actual weight.  All S197 GR40SLA cars require a steering rack change due to dimensional differences, and two racks are offered.  For vehicles driven primarily on the street, a variable ratio unit with the same gearing used on 2003-2004 Cobras is recommended.  For those that demand quicker response, we offer a very quick-responding steering rack, recommended for autocrossers, drifters and experienced road racers.  This system steers faster and more accurately than any GR40 system to date. 

    Price   Product Name   Model   Buy Now 
 GR40ST Ultimate Street <br>Rear Chassis System   $2,689.65   GR40ST Ultimate Street
Rear Chassis System
 S197 GR40ST Rear Kit  Buy Now 
 GR40TT Autocross/Open Track Rear Chassis System   $3,829.55   GR40TT Autocross/Open Track Rear Chassis System   S197 GR40TT Rear Kit  Buy Now 
 GR40RT Road Race/World Challenge Rear Chassis System   $4,573.55   GR40RT Road Race/World Challenge Rear Chassis System   S197 GR40RT Rear Kit  Buy Now 
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Please note: Prices are subject to change.
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