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MBA scooped the rest of the best when we announced Cannondales Scalpel: a 22-pound XC racer that integrates every trick in the short-travel, dual-suspension book into one fine-riding chassis (read it at www.mbaction.com). The official debut of the Scalpel will be at the Sea Otter race in Monterey, California. A handful of journalists, however, were invited to ride the bike one week earlier at Cannondale’s team camp in Alpine (a sleepy town about 50 miles East of San Deigo). The Volvo/Cannondale team was assembled there for photo ops, high-level meetings and intensive training in preparation for the season openers in Monterey and Napa.
Although Cannondale extended invitations from Thursday through Sunday afternoon, unseasonal rain and low temperatures sent all but one reporter scurrying for home by mid Saturday. MBAs editor-at-large got wind that an unplanned arrival from Cannondales R&D shop might materialize on Sunday. R.C. (the lone journalist) showed up bright and early just as the Gemini, Volvo/Cannondales radical new downhill prototype, was rolled out of its hotel-room hiding place. The following report is for loyal MBA readers eyes only:
THE GEMINI?S DOUBLE REAR SUSPENSION SYSTEM
Cannondale’s penchant for divergent designs is almost legendary, and their latest downhill chassis should startle the most calloused of the been-there-done-that crowd. Dubbed Gemini, the eight-inch-travel chassis has two separate rear suspension systems–each with its own shock. We wish that we could report on exactly how the system performs, but the prototype had not been ridden by anyone at Cannondale. Except for being short of a chain tensioner device, the bike was complete when it was rolled out on Sunday. We had a chance to spin around the hotel parking lot to check out the action of the dual-rate rear end, but that was the extent of the testing that day.
Some modifications have been made to adapt the Gemini system, beyond those details, the front section of the Cannondale DH chassis remains similar to the previous years. The fork is a pumped-up version of last years Moto DH–an inverted fork with a stroke that adjusts from six to eight inches.
Downhillers who need more facts can feast on the pictures while you read on. The following should answer most of your questions
Question 1: Why two suspensions?
When a bicycle is on level ground, bumps drive the suspension straight up. Conventional suspension geometry is designed to allow the rear wheel to travel more or less in a vertical path so it can respond to bumps easily. When a downhiller is descending a steep grade, however, braking and bump forces try to drive the back wheel in a flatter path, angled more towards the rear of the bicycle.
Cannondales head designer, Ron Litke, dreamed up the second Gemini piggy back linkage to be able to react on an angle that was more parallel with the ground. This action, he believes, will soak up sharp-edged bumps while the bike was descending steep grades–and also help keep the rear wheel on the ground when racers were dragging the rear brake through chatter bumps.
Question 2: How does it work?
The Geminis main rear suspension is a conventional monoshock-type swingarm that drives a Fox type-E coil/over damper with a 2.25-inch stroke. The rear axle is mounted to a small parallelogram linkage where the monoshock swingarms rear dropout would normally be. The parallelogram drives a Fox air shock via a machined-aluminum compression strut routed above the seatstays.
Because the lions share of bumps activate the suspension in a vertical direction (perpendicular to the ground), only the monoshock swingarm and its coil/over damper are activated in most situations.
When the bike is angled sharply downward, any bump that deflects the suspension at 90 degrees will tend to pitch the rider over the handlebars. This is when the Gemini linkage is designed to activate. The main swingarm remains in place, and the Gemini linkage causes the rear wheel to arc away from the bikes center of gravity, thus keeping the rider on line and in control.
Question 3: How will the new Cannondale pedal?
Because the Gemini linkage extends the wheelbase about two inches as it cycles through its travel, even the slightest amount of chain tension will yank it back in place and prevent it from activating. Theoretically, the new Cannondale downhill chassis will pedal like that company’s Super-V chassis. Its monoshock swingarm shares the same pivot geometry.
Question 4: Why two shocks?
Cannondales designers wanted the system to be easily tuned. Using a second shock, driven by a separate system, enables the teams mechanics to dial in the Gemini more easily. Initially, the Geminis secondary air shock will have a lockout lever to aid in tuning the primary system. Because there are two separate linkages at work, the Geminis rear wheel can travel virtually anywhere in a rough arced path that covers 18 square inches.
Question 5: What about braking forces?
When we fussed with the Geminis rear end, it seemed that braking forces tended to extend the secondary linkage. Cannondales project manager explained that Gemini was specifically designed to react to bumps independently from braking and bump forces. Parking lot tests are certainly not conclusive, and only after extensive field testing will anyone know for sure.