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Front Drive
A front-drive tandem runs the primary chain from the front bottom bracket all the way to the rear wheel. The more common rear-drive setup runs from the rear bottom bracket.
Front drive is slightly heavier, due to the greater length of chain, and in some cases the stoker's right crank may interfere with the chain. Front drive greatly reduces torsional stress on the frame: with rear drive, the stoker's bottom bracket is being pulled forward on the left by the synch chain, while being pulled to the rear by the primary chain. With front drive, the crossover takes place at the front bottom bracket, where both chains pull to the rear. Front drive also makes chainline an academic, not a practical concern. Since the chain run is so long, all gear combinations may be used without running the chain at a sharp angle.
