You need to change your brake pads to either KoolStop Salmons or SwissStop greens. I can tell you from personal experience that the salmons will DRAMATICALLY increase your braking power, and I hear the same thing said about the SwissStop greens.
Secondly, clipless pedals or toe clips and straps are a necessity on a tandem if you plan on doing any serious riding. Otherwise, this will not be the last time the stoker gets hit with a pedal, and before long ..... no stoker.
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BICYCLE - [[I]bahy-si-kuhl] - Noun :> A medical device used to correct the common geriatric condition of OFS, (Old, Fat & Slow), in a manner that does not induce brain-decaying boredom like walking or running.
2005 Trek T2000 tandem, Giant TCR, Eddie Merckx Majestic Ti, Fuji Team, Giant Revel 29er, Windsor Clockwork (Orange) fixie, and a BikTrix Juggernaut Ultra 1000 fat tire eBike