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My bike is a 2016 Brompton, I am thinking to swap current cranks. Current BB possibly is this one (a JIS square taper), model: stronglight jp400 119 mm.

http://brilliantbikes.co.uk/brompton-bottom-bracket-cartridges/849-brompton-bottom-bracket-jis.html enter image description here

According to this doc, For Brompton, ISO cranks are not compatible with JIS BB http://bromptonjunction.com/wp-content/uploads/2015/09/ds-crankset.pdf

So will this crank fit the BB? This seems to be a shortened Shimano crank (Altus).

http://www.sjscycles.co.uk/thorn-110-74-pcd-125-mm-alloy-crankset-silver-prod237/ enter image description here

The new crank need to be at exactly where the old ones are on the spindle to not to affect the folding. Are all shimano square taper cranks fit JIS BB? Also the link mentioned it's a triple, how that will affect the chain line, if I just install one chain ring (Brompton needs only one ring)?

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JIS, short for Japanese Industry Standard, is by the far more common and is the one used by all Japanese manufacturers including Shimano. As far as I know, the only manufacturers that still produce ISO cranks are Specialites TA and Campagnolo, and the latter only for track bikes.

Triple crank chainline is measured at the middle chainwheel, so you can use the number as it is.

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  • Thanks. Is the chainline determined by the BB then? so i can fit any compatible chainset (may need to adjust for double or triple chain ring) to get original chain line?
    – thotwielder
    Apr 17, 2016 at 12:42
  • The chainline is determined by crank and BB. The manual for the crank should list a chainline and BB axle length, if you need different chainline you can calculate the required BB length from those numbers.
    – ojs
    Apr 18, 2016 at 18:20

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