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Superior by Design

The GR-40 Chassis Systems

The GR-40 chassis system is simply the finest chassis package available for a Mustang. No competitor’s system, regardless of price, offers the same level of performance. Skeptical potential customers and satisfied GR-40 drivers frequently ask “What makes the GR-40 kit so superior?” The simple answer is, “It’s designed to be.”

Although we have the resources to manufacture the same stuff our competitors produce, our product offerings are driven by our engineers, not by trendy gimmicks or popular demand. Working within the physical constraints of your Mustang’s stock body structure, every chassis component is engineered to maximize chassis performance through balanced load management. Our commitment to functionality and our willingness to develop innovative solutions to handling problems allows us to deliver systems with race-car performance levels, good ride quality and modest maintenance regimes, in kit form to street car owners.

All our Mustang components are derived from geometry models and load management techniques developed using proprietary design software and the experience culled from over 35 years of combined experience in motor sports. Before we release a component into the marketplace as a production part, its prototypes have suffered through numerous tests, in prototype form, on street and racecars of every kind. Prototypes are tuned and tweaked to yield the best possible performance, durability and simplicity of installation. The finished products that you see in the following pages represent the GR-40 system, Superior by Design.


Thank you for your interest in Griggs Racing Products. We have gone to great lengths to develop Mustang chassis components that meet or exceed the output of Fords power plants. In the following paragraphs we will outline those components and give you a blueprint for turning your Mustang into a world class sports car.

The fox and SN95 Mustang’s chassis was designed in the mid-1970’s, during an oil crisis, to be an inexpensive sedan or station wagon (Fairmont/Zephyr) and not a sports car. It had to be light, cheap and easy to build. The “Fox” and SN95 unibody chassis, suspended by McPherson struts (state-of-the-art at the time) and a solid axle, did a pretty good job as a family truckster (cheap!) When the oil crunch eased and Ford stated to think about sports cars again, the only platform they had was the Fox. The new body style Mustang, born in 1979, was built out of revised station wagon parts. The Mustang was soldiered on, to the present day, with the same simple underpinnings. (For the 2005+ or S197 cars Ford did a complete redesign, although old habits die hard, see 2005+ specific articles.)

With the notable exception of dangerously unpredictable handling at the limit (fishtailing), the current chassis works fairly well. After continual tweaking by Ford, the solid axle Mustang feels pretty racy to the average driver. But you wouldn’t be reading this if you were the average driver. You may have discovered that Mustang cannot be driven at the limit. If you follow the steps laid out in this website, you can plan on owning a car that will pull over 1.0 G on a skid pad and outrun ZR-1s or Vipers in the Slalom without giving you white knuckles. By focusing on geometry and load management, we have developed a blueprint for building the perfect Mustang.

If you think this sounds an awful lot like Math and Physics, bear with us. Making a car perform well is an exercise in managing physical forces. The better you understand these forces, the easier it will be to build your pony-car without wasted time and money. Throughout this catalog, you’ll see constant references to geometry and physics and information about roll centers, camber curves, anti-dive and anti-squat. Detailed explanations of all these terms are beyond the scope of this catalog, but where necessary, we have included engineering drawings to help illustrate why our changes are so effective. If you have more detailed questions about geometry changes for your application, please contact us. Our knowledgeable staff is always willing to explain the finer points to a valued customer, (707) 939-2242.

Griggs Racing

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