Originally Posted by Retro Grouch
Well, I did that once. I built a bike that, I think, had a 48/38/28 crankset and a 14 to 18 5-speed straight block. It was kind of cool to ride as long as you could stay on one chainring but the big double shifts that were occasionally required weren't pretty. That 38 to 28 chainring shift, for example, always came at the base of a hill and generally ate up all of my momentum.
The actual gearing I have on my touring bike is: 44-34-22 in front, with 12-14-15-16-17-19-21-25-34, so I have 6 closely spaced cogs and 3 widely spaced ones. Between the granny and middle ring, there is just a little overlap, so it could be bad if I am fighting a grueling headwind (it happened once), but it works fine when climbing hills because I loose speed anyway. Between the larger gears, there is just enough overlap that I usually choose the middle ring on flat terrain, loaded or with a headwind, and the large ring on slight downgrades, unloaded or with a tailwind. And regarding the gap at the top, I rarely use the 44/12, except downhill with the wind at my back; I'm built for the long distance, not for speed!
At first, I had done something like that with the tandem : 48-38-24 with 13-15-16-17-18-20-23-26-34. Great when I had just my 9-year-old stoker, but not enough when I also had the 5-year-old second stoker. So I now have 48-38-28-18 with 12-15-16-17-18-20-23-26-32. The "18" super-granny has been used twice on 17% grades.