Originally Posted by
schnee
That's why I like a classic triple crank with a 10-34 cassette so much, you spend 80% of your time in the middle chainring, so it mostly feels like a 1x. Then, the other 15% is in the granny gear, and every once in a while get in the big ring and haul ass.
That's just it.
The middle chainring is for cruising the plains, and for handling the majority of the terrain, i.e. minor inclines down to gentle descents.
The large chainring is for the >40km/h descents.
The small chainring is for the steeper ascents, i.e. > 5%.
Assuming a 11-36T cassette...
Tourers, with heavier loads, are therefore going to be heading for a small chainring of 20-26T.
If it is desired to pedal beyond 40km/h, then a >50T chainring is appropriate.
What's left is the middle chainring, e.g. 34-44T.
One must bear in mind, that with a very small chainring, it is likely that some gears will be unavailable due to diagonal and loose chain, e.g. 20T+11T is not going to work. However, these gears are not really required. The small chainring is for ascending, i.e. to be used with 36/32/28/24T rear sprockets. Similarly, one is unlikely to use the descending chainring on the large rear sprocket. Thus, the chain should be sized on the big-big cogs, such that the derailleur system can just about stretch to cope with big-big, but is not expected to be used on it.
You then end up with the front chainring derailleur lever being used to select between ascent/cruise/descent mode, and the rear derailleur lever for fine tuning the gear in that mode.