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.
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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. | 
RATZ
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. |