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I would like to change my 7-speed twist-shift Two'sDay into an 8-speed Shimano XT RapidFire. Can I order parts through Bike Friday or should I just order a regular Shimano 9-speed cluster and 9-speed shifter and use 8 of the 9 gears? Do I need an 8- or 9-gear RapidFire shifter to change the 8 gears with 9-speed spacing?
For eight-speed/nine-speed spacing, you will need a nine-speed cassette with a suitable set of cogs. What is most common is to remove the largest cog on the cassette. With eight cogs, spaced with nine-speed spacers, the cassette will fit on the hub. The shifter must be nine-speed and there will be an extra click. You can order parts through Bike Friday's Customer Service department. XT RapidFire shifters and an LX cassette (11-28) will run you US$180 plus shipping at the time of this writing.