FRONT CHASSIS DEBATE


SHORT-LONG ARM vs MACPHERSON STRUT

WHAT IS THE BEST?


The answer to this question depends upon your perspective.

CORRECT GEOMETRY vs PRODUCTION COST

Vehicle Performance = SLA
Manufacturer Cost = Strut

Results from the Short-Long Arm front suspension is unparalleled in performance from other designs. Because of the independent articulation points at the top and bottom of the spindle...

1) Retain Strut if class rules and/or preclude budget restrict, or if car is a drag car or boulevard cruiser and cornering power is not a requisite.

2) Install SLA if maximum braking and/or cornering power, tire wear, or lowest possible ride height is the priority of design.

We will continue the front chassis debate by providing a history of each design along with their benefits below. 

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THE BASICS


All the best GT cars of consequence today, including Corvettes, Ferraris etc., and virtually all race cars with independent front suspension have short upper control arms fitted above longer lower control arms (SLA) instead of MacPherson Struts. All Mustangs* from 1979 to current utilize MacPherson struts front suspension.  The reason is not for superior handling, but to afford the automaker a fast and relatively inexpensive way to produce the car.  While struts work fine driving in a straight line or with light cornering load, inherent geometric deficiency prohibits full realizations of a tires performance, especially under high lateral load.

*65-73 Mustangs and 74-78 Mustang IIs were produced with SLA suspension, the latter being a Pinto chassis. Utilizing Struts here would be considered a downgrade, however the geometric layout of these cars are not conducive to truly high performance use on today’s high grip tire technology and they are highly compromised in a variety of other ways such as rigidity, camber gain, anti-dive, roll center stability, and large tire fitment without an excessive scrub radius.

SLA vs Strut on Wikipedia:
"SLA or double wishbone suspension provides the engineer more free parameters than some other types do. It is fairly easy to work out the effect of moving each joint, so the kinematics of the suspension can be tuned easily and wheel motion can be optimized. It is also easy to work out the loads that different parts will be subjected to which allows more optimized lightweight parts to be designed. They also provide increasing negative camber gain all the way to full jounce travel, unlike the MacPherson strut, which provides negative camber gain only at the beginning of jounce travel and then reverses into positive camber gain at high jounce amounts.

Griggs Racing SLA System for 1979-2004 Vehicles

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Griggs Racing SLA System for 2005-2014 Mustang

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TECHNICAL DETAILS


Although struts are a popular choice, due to its simplicity and low manufacturing cost, the design has a few disadvantages in the quality of ride and the handling of the car.  Geometric analysis shows it cannot allow vertical movement of the wheel without some degree of either camber angle change, sideways movement, or both.  It is not generally considered to give as good handling as a double wishbone or multi-link suspension, because it allows the engineers less freedom to choose camber change and roll center.

A strut is rigid mounted to the spindle and cornering and braking loads are usually pressed against the hydraulic piston and cylinder of the damper, degrading performance and longevity.  Additionally, it tends to transmit noise and vibration from the road directly into the body shell, giving higher noise levels and a "harsh" feeling to the ride compared with double wishbones, requiring manufacturers to add extra noise reduction or cancellation and isolation mechanisms.

SLA systems have a shock absorber that can be lighter, less complicated, and being independent of braking and cornering loads suffer no such compromises and therefore deliver superior performance.  More importantly, the roll center is stabilized.  In a strut system as the body rises and falls, as during brake dive, or rises under acceleration, the roll center migrates usually double the change in ride height. With a proper SLA system this change is minimal as ride height changes. This contributes to a far more stable chassis balance as the car transitions through the 5 zones of a corner, braking, turn in, mid float, power application, and exit. It is especially beneficial on rough or undulating courses and through esses.

The next big advantage to SLA systems is camber gain, which is the change in applied tire camber as the wheel travels up into the wheel well as the suspension is compressed. With struts the camber curve is minimal, or even regressive, actually losing camber as the wheel travels up in bump motion. So as the body rolls in a corner, compressing the outboard suspension the loaded tire loses applied camber to the road surface, reducing tire contact, and wearing the outside shoulder. To compensate, high static camber settings are needed, 3 4 or 5 degrees, to compensate for tire deflection and camber loss form body roll. But these high negative camber settings are detrimental to performance due to reduced tire foot print under braking, and inconsistent tire contact patch area during transition into and out of a corner. It also results in high shoulder wear. Most front strut cars wear out the tires shoulders, both inside and out while leaving at least a third of the tread in the center of the tire.  Griggs Racing SLA systems have aggressive camber curves designed for current generation performance tires. Static camber on race tracks seldom exceeds 2 degrees. Properly aligned, tires last much longer without the excessive shoulder wear, and performance is more than significantly improved due to the near always flat tire contact patch.

The larger and sticker the tire and the more down force applied, the more brake and cornering load in the front end. Therefore, more reason to use an SLA. The changeover to an SLA system is truly an amazing improvement to the front end of any Strut equipped car no matter how it is driven.

SLA GEOMETRY


Benefits Over Strut

  • Available for street and racing applications
  • Race winning performance, suitable for Daily Drivers
  • Simple bolt-on installation
  • Substantially increased front grip
  • More effective braking
  • Incredible steering accuracy and feel
  • Much improved front tire wear
  • Optional SN95 Spindle &  Hub for street applications (1979-2004)
  • Exceptional GR40 Aluminum Modular Spindle & Aluminum Hub system for perfect geometry 
  • Any brake caliper and rotor combination can be fitted: brackets available to mount most 3.5in calipers on 13, 13.5, 14 and 15 inch” rotors for GR40 MDS Aluminum Spindles or OE SN95 spindle with proper adapter

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

Griggs Racing Aluminum Spindles

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Our Aluminum Spindle design provides increased strength with a reduction in weight and allows for a larger hub pin. With the larger hub pin mated to our proprietary Aluminum Hub you can expect maximum performance. 

Hub Pin Size Diameter Comparison

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Several new features never offered in a spindle before are incorporated in our design. Using a large, serviceable Timken double roller Uni-pac bearing, the entire assembly is lighter and far more rigid than an OEM SN-95 or SN197 spindle and hub assembly, improving brake performance, cornering power and steering accuracy. Test results indicate 4 to 5 times stronger than OEM spindles and hubs.

Currently available with 8.7 degree KPA and 10 inch length upper and lower ball joint design, and soon to fit late model Mustang strut systems, the modular design of the spindle accommodates many different configurations and vehicle usage as well as ease of repair.

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

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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

15" Rotor & Caliper on Griggs Racing Aluminum MDS Spindle

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If Big Brake Kits are on your mind, then look no further. Our spindle was design was focused on adapting to the most commonly used and best performing brakes. Whether you are using a stock car brake, factory production brakes, or aftermarket solutions - we can guarantee the only limiting factor will be caliper clearance between your wheel rim.

Also available are stainless steel brake brackets, hats and rotors for Griggs Racing Brakes, Wilwood, Brembo, Alcon, Baer and any other and any other popular brand caliper with 3.5" 130mm (SN95) or 150mm (S197) caliper mounting pattern

Lose Up to 110lbs & Gain Increased Clearance

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Lastly, Wider Tires can be used to further increase your front tire contact patch - in addition to the already increased contact patch from proper articulation and geometry.  The 2" drop and overall design allows use on SLA systems with upper ball joint inside wheel, allowing wider front tires.  Without having to replace your factory fenders, it is possible to fit tire widths up to 315mm!

SLA Assembled w/ MDS Spindle & SN95 Hub

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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. 

MAXIMUM PERFORMANCE


Because the SLA Geometry allows for independent articulation...

Names include Short-Long Arm, Double A-Arm or Double Wishbone suspension, 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.

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 GR40 SLA 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. 

 

Rigid
Each 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.

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!

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. 

STRUT GEOMETRY


MANUFACTURER PROFITABILITY


The MacPherson Strut was adopted by factory production because of its cost effectiveness in production and assembly times, where every penny and second counts in order to increase profits.

Koni Front Struts

The two most important elements in a performance chassis are the tires and shocks (or struts).  Dampers are a better term as their primary purpose is to dampen motion of the chassis.  So far only Koni provides the quality and performance we demand of dampers to be included in a GR40 Kit.  And then only in units that we have custom built to our specifications. 

Proven by over 50 years of international competition including Formula One, and the only part of our GR40 systems not made in the US, The Dutch company is owned by the US conglomerate, ITT automotive group.  Griggs Racing has worked closely with Koni in developing shocks and struts over the years that do exactly as required in delivering a serious performing chassis while improving handling, traction, ride quality, tire life, and safety.  Also, they live virtually forever with very little service required.  Koni’s are an investment you will have for a very long time.  They are not “throw away” shocks.

Most replacement strut brands on the market usually “feel” pretty good upon replacement but after a short time their “low speed” damping characteristics degrade and handling goes away.  Plus most all are made with inadequate low speed damping for high speed performance, especially on compression. Lesser quality struts are unable to provide the level we seek in offering the best performance in chassis kits and options.  And the adjust-ability is easy, if you follow our instructions. 

With valving perfected to suit our standards, and the win record of GR40 cars to prove the point, these are a necessary step to tuning any 70-04 strut equipped Mustang chassis to perfection.

Special Double Adjustable Damping Curves:  More digressive compression curve and simple on car adjust-ability of rebound makes this the serious club racer’s choice.  Quickly adjust for track use when high speed control is the main requirement , and then back to street use when the best ride is the priority.

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Griggs Racing Strut System for 1979-2004 Vehicles

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15" Rotor & Caliper on Griggs Racing Aluminum MDS Spindle

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Griggs Racing Strut System for 2005-2014 Mustang

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How We Improve Strut Systems

  • Available for street and racing applications
  • Race winning performance, suitable for Daily Drivers
  • Simple bolt-on installation
  • Substantially increased front grip
  • Incredible steering accuracy and feel
  • More effective braking
  • Much improved front tire wear
  • Utilizes stock SN-95 spindle and hub on street applications
  • Can be used on GR40 Aluminum modular spindle and hub system for perfect geometry 
  • Any Brake caliper and rotor combination can be fitted. Brake brackets available to mount most 3.5 inch pattern calipers on 13, 13.5, 14 and 15 inch” rotors on GR40 MDS series or SN-95 spindle with proper adapter

 

BUILD YOUR CHASSIS


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.

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