Thread: Birdy thread
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Old 02-09-19, 02:05 AM
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glye
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Originally Posted by secret_squirrel View Post
In other news all the parts I needed arrived to convert my 10 speed Mk3 Touring to 11 speed, whilst retaining the high speed 9t cog. More to come unless anyone has posted about this before. Have 2 cassettes a 36-9 which is super wide range and a 32-9 which is the same range as the 10speed touring but with an extra close ratio.

Is anyone interested in the story once it's built?
I am! Also interested in how you plan to do it. My Birdy has the 9-32t 10-speed cassette originally, am considering the 9-36t 11-speed for a more usable range.

Which derailer are you going to use? My concern is that the cassettes are MTB-spaced, and 11-speed MTB derailers all seem to be so long that they may rub the tire, since 11-speed MTB cassettes are dished so that the biggest cog is further inboards than the biggest of a 10-speed.

SRAM has a CX 11-speed derailer "Force CX1" which is nicely short, but it's rated for 32t max, and 21t chain wrap. B-screw may allow the 36t cog, but stretching it to 27t chain wrap seems a bit much. And you'd have to use road shifters, or an adapter.

On the other hand, the MTB 11-speed derailers are designed for 40-50t big cogs now, so they may be riding too low for good shifting on 36t max. And the Birdy prefers to have the chain on the short side, for better chain wrap when folding. Short chain means extra large distance between cassette and derailer, due to offset pulleys. It would be interesting to mount the short cage from the CX1 on an MTB derailer body, if that fits. But it's an expensive bet.

Annoying that Sunrace who makes these 9t cassettes, don't seem to make a derailer that's designed for them, and the small wheels they're meant for.
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