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- or 10-speed is the sweet spot for touring today.
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 bigger chainring. For uphills, including hills that level off for a bit and then continue up, stay in the smaller 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...
You'll find Sheldon Brown's Gear Calculator indispensable when you're thinking about gearing.
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. If you know me, talk to me before going this route for more info.
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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