This article explains why using a double is an excellent choice for the crankset (the chainrings at the pedals) for touring bikes, at least the kind suitable for worldwide self-contained road tours.
|My 1985 Trek 720 (original brochure) with brand new gearing in 2015: 24/40t crankset, 11-32t cassette|
Ideally, touring bikes would come with just a single chainring. Shifting would be much simpler... just move one lever one step to get to the next gear. But we're not there quite yet... we'll need an affordable 10-50 cassette to give a good range (18-100 gear inches, for you bike-math geeks). And frankly, we may never get there for touring bikes... you'd need at least an 11-speed cassette so that your gears aren't too far apart, but a 9-speed is the sweet spot for touring.
The vast majority of touring bikes have triples... three chainrings. I wish I could find the good article which critiques the average triple. In short, it said many triples have three lousy chainrings: the lowest one is not low enough, the middle one is unneeded because it offers nothing new, and the highest is too high (unless you're a pretty strong biker).
A double is the perfect compromise; think of it as a single, but with an extra chainring for uphills. For flat land, down hills, and even slight uphills, simply stay in the larger chainring.
The advantages of a double over a triple are:
These are not huge things, but small things that add up. The main thing you give up by not having a triple is a little range... approximately the loss of the highest gear, which is rarely used anyways.
|22/40t crankset, 11-32t cassette|
I think a good gearing scheme is a 22/40t double crank with a 9-speed 11-32t cassette (assuming 700c wheels; if 26 inch, use a 24/42t instead). It's recommended that you pedal from 60 to 90 rpm (revolutions per minute), so...
Unfortunately, wide range cranks like 22/40t are not available off-the-shelf. Fortunately, they can[*] be built up using parts from Dimension, ordered complete from White Industries, or created by substituting a chainring on an existing double crankset.
[*] It remains to be seen if you can go as wide as 22/40t (I will update this in early April if it didn't work out), but 24/40t does indeed work (see photo).
Check out my article about touring bikes if you're thinking about buying one. It has a little more information about gearing.
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