Design and Fabrication of the Rally Twins

Before any fabrication was done, we invested hundreds of hours of engineering and CAD design to ensure the Rally Twins would be durable, light, and maintainable. We selected the major components and integrated them into the final package - the goal was to meet every design criteria that was set out in the beginning (see the history page).

Ergonomics was of particular concern during the design. The Rally Twin had to be comfortable for long freeway rides, and be equally comfortable for standing up over long distances. The Rally Twin also had to be comfortable and capable for two-up dual sporting. Designing the Rally Twin to accomodate all the desired features proved to be a monumental task. There was no room for give and take. It all had to work, and to work well.

One of the most important design features of the Rally Twin frame is the attention to detail with respect to fatigue design. Every joint was evaluated, and welding and gusset designs were employed to increase the ruggedness of the frame while retaining a light, efficient design.

A meticulous, detailed philosophy was followed during the fabrication. We machined every joint on a mill for a precise, close fit-up prior to TIG welding. Every weld was pre- and post-heated to eliminate embrittlement in the weld zone. The Rally Twin frame is not just a frame, it is a work of art, an exhibit of fine craftsmanship and engineering detail.

While the frame is the heart of the Rally Twin, it was only the beginning of the fabrication effort. The intake and exhaust system was designed to move the revvy EX 500 power back to the midrange, optimized for dual sport use. A custom aluminum airbox, with quick access dual foam filters, charges the engine. The exhaust is a 2 into 1 stainless steel design, TIG welded and back purged to provide free flow, but more importantly tuned for the desired power range of the Rally Twin. The muffler is USFS spark arrested, with a sound level of under 90dB.

Following fabrication, the design was verified in grueling test sessions at the motocross track. The Rally Twin was ruthlessly bottomed and cased out, to transmit the maximum possible stress to the frame. The stress on the frame was measured by strain gauges, attached at locations of maximum stress. The strain was recorded by an on-board data recorder, which was then downloaded into a portable computer and analyzed.

Since then the Rally Twins have endured two years of intense field testing, allowing final optimization of the frame design.