For some time I was planning to build a fast commuter, a simple yet elegant bike that I would use to get around the city, do shopping, go swimming etc. The city I live in is mostly flat but it is surrounded by hills on 3 sides (4th side is a lake) and quite often I need to get over some hill to get things done. I tried fixed gear for some time which was pretty fun but quite useless when I need to go vertical. So a FG/SS won't do the job for me.
I'm looking to build an easy on the eye (yet beautiful) bike so derraileurs are a no no. I was thinking of other options, like an Alfine 8 or Alfine 11 Di2 which are both expensive and not exactly what I need.
Last night I came up with the idea of building a two speed that is, one cog in the back, a chain tensioner and a double crank (thinking of 50/39)
Since aesthetics are a pretty important part of this project, I thought I could go with SRAM hoods, an s500 or s900 right lever and a Rival left shifter. They're almost identical and even someone with a trained eye wouldn't notice the difference without mentioning. A blade swap might be necessary but that's doable.
Then I thought, why not combine this idea with this:
This would give me 4 unique gear ratios and a semi-automatic drivetrain. With a 22t in the back you get the following ratios:
[table="width: 500, class: grid"]
[tr]
[td][/td]
[td]50 (1.0)[/td]
[td]39 (1.0)[/td]
[td]50 (1.3)[/td]
[td]39 (1.3)[/td]
[/tr]
[tr]
[td]Gear Inches[/td]
[td]60[/td]
[td]46.8[/td]
[td]82.1[/td]
[td]64.1[/td]
[/tr]
[tr]
[td]Gain Ratio[/td]
[td]4.4[/td]
[td]3.4[/td]
[td]6.0[/td]
[td]4.7[/td]
[/tr]
[tr]
[td]MPH @ 80 rpm[/td]
[td]14.3[/td]
[td]11.1[/td]
[td]19.5[/td]
[td]15.2[/td]
[/tr]
[tr]
[td]MPH @ 90 rpm[/td]
[td]16.1[/td]
[td]12.5[/td]
[td]22.0[/td]
[td]17.2[/td]
[/tr]
[tr]
[td]KPH @ 80 rpm[/td]
[td]23.0[/td]
[td]17.9[/td]
[td]31.5[/td]
[td]24.5[/td]
[/tr]
[tr]
[td]KPH @ 90 rpm[/td]
[td]25.8[/td]
[td]20.2[/td]
[td]35.4[/td]
[td]27.6[/td]
[/tr]
[/table]
The IGH shifts with centrifugal force so one concern I'm having is that not all 4 ratios would be usable. Some other post explains how the shifting speed can be adjusted by changing the spring tension of the hub.
Of course no one knows how it will ride until someone builds a bike like this but I want to hear your opinions.
Is this a stupid idea?