Radd Through The AgesChanging 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.
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.
First Radd PrototypeThe 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.
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.
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. | 
RADD MC2
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. |