Originally Posted by
Jurgen
A compact double has a smaller inner chainring than a standard double. It's a good compromise for those who prefer to spin their way up hills (rather than mash) but don't want the added weight of a triple. To be honest, I don't "get" the point of a compact double on a commuting bike. (On a road bike, yes.)
A routine compact setup of 34/50 mated to a 12-27 10spd cassette would give you a gear range of 33.7 to 111.5 inches.
A standard triple has a 20 tooth differential (30/39/50 for most road triples) so at the low end you would gain 4 gear inches of advantage over a compact double mated to the same cassette.
Is 4 gear inches (29.7 vs. 33.7) at the low end, and a range of gearing on the 39t ring which can be accomplished by variable crossing on a compact double really worth the extra weight, maintenance problems, and added Q-factor of a triple crank? If you really need the extra-low ability of a triple, and you're going with a trekking/touring setup (26/36/46 or better in the case of 22t capacity derailleurs) then a triple makes sense. If you're not carrying the monster touring loads around, then the difference between a road triple and a compact double is negligible, even for large hills.
I'm partly biased because I'm building a compact double equipped bike, but I've based that decision on having a 26t granny ring on my current bike (and I never use it) and a 39-26 low gear on my road rig (which isn't quite low enough) so something in between will work fine.