Hello Touring Collective,
I'm currently in the process of building a LHT with the intent of some progressively longer tours over the next two years; I hope to ride trans Am in 2010. I have no experience at building a bike from scratch myself and am working with my LBS to get this new machine fully functional. My questions relate to drivetrain; specifically what range of gearing is even feasible to pursue and how to do so. Here are some pertinent specs on the bike as it now stands.
- 62 cm LHT frame
- Shimano Ultegra STI shifters
- Shimano XT Deore Rear Derailleur
- Shimano XT Deore Cranks
- Three chain rings - 48/36/24
- SRAM 9-Speed Cassette 11-34
- SRAM PC-991 Chain
We attempted to use a Shimano XT front derailleur but apparently it was unable to shift across the whole range of rings in the front. Right now the bike is equipped with a Shimano SORA in the front, which does access all three rings. To make this work the smallest ring had to be reversed from its normal installation, and apparently the cranks are 5 mm out of symmetry because of this.
It is clear that this configuration will not support all 9 cassette positions with all three chainrings. If the bike is on the smallest ring, only the 4 largest cogs on the cassette are usable before the chain loses all tension. With the largest ring and cog selected, the real derailleur appears to be over extended.
1 - Is it even feasible to pursue this wide-range gearing configuration?
2 - If the answer to 1 is yes, can you provide any recommendations on components to accomplish this?
3 - Is the lack of symmetry between the cranks anything to be concerned about?
As always, thanks for any advice or guidance you can provide.