Bike bottom brackets: square tapered, Octalink, BSA / MegaExo, Pressfit, BB30 / PF30. Shimano

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Deput post - Hello!!

Thanks for the video - I watched with interest but length is a factor nobody seems to commit to - perhaps a good video topic I am sure several struggle with this!


I am building an XC bike for my 11yo girl from new and as-new re-purposed parts, and my plans are for 

TWITTER frame (26 or 27.5 compatible), bottom bracket width is 68mm, threaded


SLX 1x11 (11-42) / SLX shifter and mech

26" Shimano M15 wheels (for now)  Ardent/Ikon

Toseek bars/stem/post

Shimano M395 brakes

Basic velo saddle

all above fixed


Variables are the crank (choice here) and bottom bracket (yet to buy);

Shimano Octolink (3x stripped and given a 34t or 36t ali single ring) - this needs an octolink BB


Truvative 1x (steel 38t removed, 34tor 36t ali single ring) - this needs a square taper BB


Finding the balance in theory for the correct BB lengths has me concerned - as real low gears are likely to be rarely used but irritating if slipping off back-pedaling, high gears more likely to be used (9/10/11) on trips.   Use for the bike would be cycle paths, gentle trails, some climbs, much flat as I am trying to build my youngest daughter's interest in cycling!


Personally tending towards octo/113mm, but inexperienced with 1x.  Any experienced tips welcome!


Hopeful - Graz


btw - this will replace a small frame GT Avalanche 2 (14kg), sweet child bike but heavy...




Edited by Graz
missed a bit : )

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On 10/23/2018 at 2:02 AM, Graz said:

34t or 36t

I would start with the chainrings, Graz. I've been riding the 32T chainrings with 10-50T cassette so far. Are you sure 1x drivetrain with 34 or 36T will be OK for you daughter? Otherwise, the Octalink should be a bit lighter and just more up-to-date BB.

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