I'm in the process of setting up a touring bike and I'm a bit confused on the gearing. Looking at the specs for many touring bikes I've noticed that 27 speed (3x9) is the norm. Does anyone tour on 3x7? Seems to me like 21 speeds is plenty but then again I've never toured so I'm not fully aware of what is needed. What kind of gearing range should I look for in a 3x7 if I wanted to tour?