GSX-Radd P3 - Raddical - The Future Of Motor Cycling

James Parker's GSX-Radd Shows The Future Is Now

Rumors of the telescopic fork's death have been circulating since the late 1970s. Still, the venerable tele lives on. Refined, tweaked and optimized, today's beefy, inverted, nitride-plated cartridge units would nonetheless be instantly recognizable to any Norton mechanic circa 1938.

Where just about every other part of the modern motorcycle has evolved, far from its roots, somehow here in 2007 we've still got the fork. Miraculously, it's still found on the front end of every championship-winning Grand Prix racer. How can this be? Mainly because it works. And with the application of immense design and materials technology, it works really well.

But suspension designer James Parker believes we can do better. He's doing all he can to hasten the "end times" of the fork. And his latest prototype, the GSX-RADD P3, is ready to accelerate the process.

Parker puts it this way: "About 70 years of refinement has kept an outdated design alive. It'd be like the car guys hanging onto the live axle they've had since the covered-wagon days. If you applied the latest technology and materials-carbon fiber, titanium and computer modeling-you'd probably end up with a really good live axle." But that wouldn't make it any less of a relic. That's because the double-wishbone and multi-link alternatives are so much better.

The fork has had a hell of a run, and as motorcyclists we've all either learned its quirks or fallen off a lot. By virtue of our learned programming, a fork is a large component of what makes a motorcycle feel like a motorcycle to us. But Parker believes we're satisfied with it only because we know nothing of life beyond the fork. Fighter pilots in 1943 no doubt thought their P-51 Mustangs were the bomb. But they hadn't flown an F-86 Sabre in '51. Or an SR-71 Blackbird in '66. In a few short years, the game can change completely. And when it comes to front suspension, the game is long overdue for change.

From an engineering standpoint, the fork frankly sucks. Since it's so tall, loads at the front tire contact patch are greatly magnified by the time they reach the steering head. That means the fork and frame must be fat and heavy to resist the forces. And much of that structural weight is far from the machine's center of gravity, further slowing the bike's steering response. And since the entire fork assembly turns with the front wheel, it adds considerable mass to direction changes. Stiction-the binding of the inner and outer fork tubes due to bending loads-makes the suspension less compliant. And the fork also adds to front-end dive under braking, since the wheel travels rearward as the suspension compresses. The more braking Gs you pull, the harder it wants to squat. We could go on, but your eyes would glaze over.

Parker has been working out the solutions to these problems since Ronald Reagan was still slapping Nancy on the ass. In broad strokes, Parker's four unique front-suspension prototypes, a Yamaha production bike and a heap of patents spanning 25 years share some key features. First, the front wheel is carried on an automotive-style upright. The upright provides a mounting point for the front brake caliper(s) and pivots on a pair of suspension arms-one high and one low. The position of the suspension arms has evolved over time to meet the demands of MotoGP-caliber lean angles, conventional steering lock for low-speed maneuvering and room for big, dual-disc brakes. The lower arm in Parker's designs has migrated from about axle height to a position just above the brake discs. All versions of his RADD front suspension have a single-sided lower arm that allows the wheel to be removed without disturbing the brakes or suspension, as on an automobile.

Parker is by no means the only person to develop a replacement for the fork. Witness Bimota's Tesi, BMW's Telelever and, more recently, Duolever, patterned after the 1970s Hossack. As Parker's RADD system took shape, he worked on avoiding the problems inherent in other alternative-suspension designs. The most vexing was how to steer the front wheel without resorting to a complex linkage akin to a heim-joint display at an Oshkosh AirVenture Flea Market.

In the world of alternative front suspension, every link, bearing, axis change and wad of bubble gum in the control chain between the handlebars and the contact patch contributes to play, friction or unwanted "bump steer" as the suspension moves or the steering angle changes. Parker's solution was to chuck all that trash and replace it with a precision assembly he calls a steering shaft. The steering shaft transmits the rider's steering inputs from the handlebar directly down to the upright that carries the front wheel. Bearings in the steering shaft allow the assembly to telescope freely to accommodate suspension motion. These same bearings transmit steering torque with essentially zero play. Good enough for high-speed CNC milling machines that operate for zillions of cycles under high load and tight tolerances, these bearings are at the heart of what makes the RADD system unique.

Like Parker's previous suspension prototypes, the GSX-RADD P3 is based on a conventional production machine, in this case a 2006 Suzuki GSX-R1000. Since the goal was to demonstrate the front suspension's performance versus the stock bike's, there are few alterations that don't relate directly to the front suspension. Engine, exhaust, brakes and rear suspension all remain stock.

But from the midpoint of the motorcycle forward, you'll find only a few familiar bits. The entire front of the standard aluminum-alloy frame has been binned. In its place is a pair of billet-aluminum plates that bolt to each side of the engine. Short struts on each side of the bike tie these plates into the rear section of the stock frame to boost stiffness. The side-plates carry the mounts for the two front suspension arms. The upper arm is a tubular-steel assembly, while the single-sided lower arm is a fluid shape built up from steel and billet-aluminum machinings. Another billet piece rises to support the handlebar assembly and provide a mount for the upper end of the fully adjustable hlins shock. You can fine-tune damping and preload while you ride.

To provide clearance for the front shock, a new carbon-fiber fuel tank and airbox cover were developed to replace the steel stock tank. The riding position is unaltered, and the clip-ons and hand controls carry over from the stock bike. A RADD-signature telescoping steering shaft carries steering inputs down to the billet-aluminum upright that carries the front wheel. The stock Suzuki dual discs and four-piston calipers are positioned on either side of the upright. Upgraded brake components would fit, but at this stage of development, Parker wants to understand how the suspension affects braking performance, A vs. B, with no cheating. The dished front wheel is quickly removable via a single large nut. For an endurance racer, this is huge.

Compared to a traditional fork, the RADD front end looks complex. But in key ways, such as the load path from the wheel, it's actually simpler and more direct. It's also lighter: At 383 pounds dry, the GSX-RADD is 22 pounds lighter than an otherwise identical GSX-R1000. Some 9 lbs. of that weight savings is attributable to the carbon-fiber fuel tank, but that still leaves the suspension and related structure 13 lbs. lighter than the stock components.

Stripped of its bodywork, it's easy to see how the RADD design eliminates a lot of heavy components a conventional bike carries high up and far from its center of mass. That greater mass centralization improves the GSX-RADD's ability to change direction. Even at a stop, the reduction in steered mass is remarkable. Without a big fork whipping back and forth with handlebar movement, steering effort is radically reduced-more like a 125 than a 1000.

In this design, based on his third series of patents (thus the P3 designation), Parker set out to make significant advances in steering feel and tire feedback. The key was reducing friction so steering geometry could do its work freely. Earlier RADD designs have used a spring and damper acting on the lower arm, which in turn was connected to the upright via an automotive-style ball joint. Though durable and strong, these joints generate significant friction. In cars with power steering and no inherent urge to tip over, a bit of friction is not a problem. But in a motorcycle, friction numbs the effectiveness of steering geometry that keeps the whole rig magically balanced on two wheels. With a fork or with alternative suspension, less steering friction is better.

On the GSX-RADD, the tubular-steel upper arm takes suspension loads. Its connection with the upright isn't a ball joint, but a new low-friction needle-bearing assembly. This upper-arm pivot makes for a significant reduction in the amount of force required for steering. Not only does this reduce steering effort at the handlebars to the level of a conventional fork or less, it also allows the machine's natural stability (due to rake and trail) to be more effective. The result is lighter, "purer" steering. For the more lightly loaded lower pivot on the upright, a large spherical bearing takes the load.

We got a chance to sample the GSX-RADD at two different venues: Buttonwillow Raceway Park in California's Central Valley and Sandia Motorsports Park near Albuquerque, New Mexico. With less than a hundred miles of shakedown testing showing on its odometer before our first ride, the GSX-RADD is in the dawn of its development program.

For something so exotic, the GSX-RADD acts almost completely conventional. It starts with an ignition key just like the stocker, and has the same steering lock as the standard bike. Low-speed maneuvering feels natural, and the reduced steering mass is immediately apparent, particularly during large, sudden bar movements. The reduced overall weight and more centralized mass also work to make the 1000 feel more like a 600. These factors may also be why the GSX-RADD steers quicker and feels more responsive than the stock Suzuki, even though Parker purposely designed the prototype with stock steering geometry and wheelbase figures to make A-to-B comparisons more meaningful.

Unlike some other alternative designs with more roundabout steering linkages, the GSX-RADD's steering feels very direct, and offers precise feedback. Suspension compliance and ride comfort are comparable to, or better than, a fork. Under braking, Parker's system is designed to offer reduced brake dive to retain greater suspension travel to handle bumps. The moderate brake dive feels natural to riders reared on forked bikes, and combined with the stock Suzuki brakes gives the bike impressive stopping performance.

Motorcyclist's designated Prototipo Piloto Barry Burke worked up a good turn of speed at the Sandia test, but was reluctant to push harder. A vague feel under high cornering loads and an energetic case of steering oscillation capped his confidence. Neither problem had materialized in initial testing. The problem took two test sessions to isolate, but it's been identified, new parts have been designed, and they're being machined as this is being written. When development is complete, we'll put the GSX-RADD up against a stock GSX-R to see just how it stacks up.

The GSX-RADD differs from Parker's other prototypes in one other significant way: This is the first one you'll be able to buy. Once development is complete, he intends to build a limited number for track-day use (though they will retain full street equipment). At about $50K, the bikes won't be inexpensive. Still, there are several other boutique bikes out there-with less exotic credentials-that cost more. And Parker plans to develop conversions for other popular sportbikes as well.

The future is coming to a track-day near you. And you may be riding it.

Radd Through The Ages
Changing The World, One Prototype At A Time
James Parker has been reinventing the motorcycle for 25 years. A master fabricator, the Santa Fe, New Mexico, resident designed and built a number of roadracing chassis in the '70s and early '80s. Every one of them had a fork. Then he began designing a swingarm front-suspension system for street and roadracing bikes. Parker was granted a number of patents on the design, formed a company called Rationally Advanced Design Development (RADD) and set out to build a running prototype to demonstrate the technology to manufacturers. The rest is history.
First Radd Prototype
The first RADD prototype was developed in 1984. Based on a Honda XL600R single, Parker assembled this hand-built machine in his Santa Fe workshop with little more than a lathe and a torch. The machine was shown to the U.S. offices of the Japanese companies, and was track-tested head-to-head with a stock Yamaha SR500. Then-future World Champion Wayne Rainey hot-lapped the prototype and proclaimed the RADD bike superior to the Yamaha. As impressive as the first prototype was, it left unanswered the question of how this system would work on a fast, powerful multi-cylinder machine. John Porter, a product planner at Yamaha Motor U.S., saw potential and would be influential in the design's future.
The Loyal Opposition
How does the RADD P3 system stack up against competing systems already in production? Compared to the BMW-Hossack system used on the K1200 models (above), the P3 offers more wheel travel, reduced steered mass and a shorter load path for suspension forces. The RADD system, with its telescoping steering shaft, also avoids geometry changes in the BMW's folding-bar steering links. It also offers easy one-nut wheel removal.
The Bimota Tesi/Vyrus (above) uses a center-hub steering system that requires a comparatively complex linkage. Center-hub systems in general use very small steering bearings, necessary because there isn't much room in the hub. Also limited are steering offset and lock. The RADD setup boasts more direct steering, greater latitude in steering geometry and greater steering lock. Wheel removal is also far easier.
To answer those questions about powerful four-cylinder applications, Parker developed the RADD MC2 (say "MC Squared") from a Yamaha FZ750. Yamaha's Porter took the point in a cooperative effort between Parker, Yamaha Motor U.S. and GKDI, Yamaha's favored styling house at the time. The MC2 was impressive in appearance and technology. It made its world debut on the cover of Motorcyclist's July '87 issue. A more developed design that retained the same fundamental layout as the first prototype, MC2 displayed the same virtues: precise steering, compliant suspension and excellent stability, particularly under braking. It traveled to Japan in secret for exhaustive testing and evaluation at Yamaha and passed.
Yamaha GTS1000
The relationship with Yamaha that began with the first prototype and blossomed with the MC2 eventually led to the production Yamaha GTS1000 as a 1993 model. Licensing Parker's patents, Yamaha Japan designed and developed the GTS to be a high-end sport-tourer. The suspension performed as advertised, though the GTS's weight and cost were strikes against it. Not intended to be a racer, a couple of GTS1000s were campaigned in America and Europe nonetheless. The GTS still has a genuine cult following, especially in Europe. England's Bike magazine recently named it one of the 50 coolest bikes of all time.
Concerned that the GTS gave the impression his RADD suspension was strictly for touring use, Parker set out to prove the viability of the system for racing. The RATZ prototype was built from a Yamaha TZ250, and included sufficient design refinements for Parker to consider it a second-generation design. Repositioned suspension arms eliminated the cornering-clearance issues of earlier versions, and dual front disc brakes were used for the first time-all previous examples employed single front discs.
Although we experienced some instability, the GSX-RADD impressed us with highly responsive steering manners.
More than a year in development, the GSX-RADD is built from a Suzuki GSX-R1000. Designed to showcase the RADD P3 third-generation suspension system in the largest sporting class, the GSX-RADD has further design refinements that tighten up packaging, improve mass centralization, sharpen steering response, reduce steering friction and overall weight. When development is complete, Parker will be offering built-to-order P3 machines based on the Suzuki GSX-R1000 and other popular liter-class sportbikes.