Brakes were such a problem on tandems. I recall coming down Cole Grade in San Diego's backcountry in the about 1973 on my '50s-vintage Follis with upgraded equipment. On the straightaway, a car clocked us at 55 mph, though I was riding the brakes to keep the speed down. (Cole Grade is a bottom-drops-out YEEHAW! with two long straights and a high-speed sweeper between them. SWEET!) The brakes at the time were the original Mafac Tigers with new Mafac pads. Smoke was pouring off. When we reached the bottom and were catching our breath, a single that we had dropped caught up with us and said there was something wrong with the rear tire. Sure enough, the Michellin 50 cotton on a Weinmann rim had overinflated from the heat and the bead was riding over the edge of the rim for some inches. Scary.
Phil introduced his disc drag brake around that time, which would have been appropriate for such descents. Best I had, though, was a personally created aerodynamic drag brake mounted very high on the bike-rider system: http://picasaweb.google.com/
Kevin Montgomery
San Diego, California
Presenting less frontal area these days