jimmuller 

I suspect people often miss the essential point on the subject. So here's what I think, without going into lots of numbers which sort of obscure the point.

First, a disclaimer: Though we have a 1-1/2 step crossover 3x5 triple on our tandem which works well for us, I've set up all my solo bikes with doubles, generally compact but not necessarily.

I start by finding a way to get whatever low gear I need as essential. After that, whenever I contemplate double vs. triple I come up to the same conclusion: The determining factors are high gear and gear spacings. Do I need 105 gear-inches? Or 90? Or what? So what should the next largest chainring be? If I can get an acceptable high gear and decent crossover spacings with just one more ring, what would be gained by using a triple instead? Really, nothing. Another ring would let the middle ring be smaller than the big ring on a double, and the triple's big ring would be bigger than the big ring on a double. But if the double's high gear and intervals are fine already, then there is no real benefit. I'd be carrying the extra ring with nothing gained, and the front shift would be three-state instead of binary.

The reason the triple works on the tandem is that we really do use the full range of gearing, slow uphill, fast down even on gentle downhills. My solo bikes don't have quite as low a low, and I don't need so much high either.