We will have to get some real world data to find out if adding another belt that is sliding along the first belt, and rolling over two more rollers, gains more from rpm control than it loses in friction.
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If you really want to shift, a manual trans and a chain drive will be more efficient but not as simple or maintenance free as a standard CVT.
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It looks like Suzuki implements their selectable ratio trim on the factory system for the Burgman 650 by tightening or loosening the tension of the contra spring with motor driven gears. Which eliminates the extra belt and pulleys.
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GLOBAL COMMUNICATION MAGAZINE | Global Suzuki
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