I got a used MKII Birdy Light, whose 56T single chainring I'd like to replace with a double eg. 56/40T.

Using a Litepro derailleur and a B-series Litepro clamp, it look like the fork won't move far enough outward to reach the outer ring.

According to the datasheet, the bottom bracket is a 113mm, TH BB-7420ST.

On a Birdy (Light), has someone successfully replaced the single chainring with a double? What derailleur did you use, and did you have to replace the bottom bracket for a wider one?

Thank you.

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Edit: Another issue is the seat slides down unless I tighten the clamp really hard. Cleaning the seatpost + inside with a clean rag and degreaser didn't help much. Any idea what I could try?
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Edit: One more question: Using this crank puller, I was unable to remove the crank, with the Birdy Light supposedly using a 68x113mm TH Industries BB-7420ST bottom bracket.

Should I try harder, or are there different pullers to match different square taper bottom bracket axles?


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Edit: It was the right puller. The cranck was just super tight.