My wife and I can out-climb most of the riders on our regular riding group, but not the climbers (which would include me on a single). Our tandem is heavier than 2x my single, though about 2x our two former singles, both mid-80's full campy racing bikes. But there is no question that for a long climb, we are at a disadvantage just because of differences in output. When she decides she is "done", no amount of effort on my part can make up for it. To each rider, a tandem doesn't respond like a single bike, because the other rider is just that much out of synch. When we happen to hit it right in some situations, it feels great, but I think it will be years before we get that magic a lot of the time.