Their patent is pending on *same side belt drive configuration*, which has not been done before, and takes a specialized design to accomplish. Paketa web site even cites the century old design (prior to about 1970 when rear shifting was introduced) as one of the things that got Paketa thinking about it. Dave even owns one of the original 1800's tandems with right side chain; the one pictured on the Paketa web site. Dave will, I am sure, respond more thoroughly than I.