Odd Size Bottom Bracket

[Delta4]

I have an odd size 68 x119 threaded squared tapered bottom bracket that is hard to find. My choices are a 68 x 118 or 68 x 120. Which size would you recommend for a 24sp with a 3x front crankset?

 

[BikeGremlin]

I have an odd size 68 x119 threaded squared tapered bottom bracket that is hard to find. My choices are a 68 x 118 or 68 x 120. Which size would you recommend for a 24sp with a 3x front crankset?

Hi,

I will start with a short digression (the details and caveats):

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Note (just in case, to avoid mistakes):
Cup-and-cone bottom bracket axle length is not always matching in length when finding an appropriate cartridge BB alternative. In that case, I usually go with this rule of thumb, and check when I mount (and use a shorter/longer BB axle model if the first one doesn't provide me with an optimal chainline).

The list from the above-linked rule-of-thumb (from the article):

• 110 mm for single chainring cranks (single-speed and 1x).
  For example, a 110 axle will result in a 46 mm front chainline; 113 will give you 48 mm; and 117 will give a 50 mm front chainline.
• 110 to 113 mm for double chainring cranks.
• 122.5 (122 ~ 123) mm for MTB triple cranks.
  Sometimes, depending on the rear chainline, a 117 mm axle length can fit better.

Another tricky part is the difference between the JIS and ISO square taper profile.

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The above noted digression is why I'm reluctant to provide a "straight answer" (too many what-ifs, no idea of the BB or cranks model). If I had to make a guess, for most modern square taper triple cranks, if you go with a Shimano square taper bottom bracket, I would recommend using a 122 to 123 mm long axle.

Relja