When measuring the axle length of a square taper bottom bracket, can I pick a new octalink bottom bracket with the same axle length?

I can think of some offset added or removed by the difference how the axle is mounted to the crank.

The crank set will be replaced too, of course.

  • BBs have some properties. Length is only one of them. you have to measure it's length, it's spindle length, otherwise you can get to "front derailleur doesn't shift to x gear.
    – Alexander
    Commented Dec 31, 2015 at 16:41
  • I guess the length is clear in my case: 68 mm, like in this type Commented Dec 31, 2015 at 17:23
  • It's not 68 but 118.5mm length. But again, you should compare the spindle length especially drivetrain side.
    – Alexander
    Commented Dec 31, 2015 at 17:41
  • 1
    There can be a difference between cranks even of the same type of interface. Place a straight edge across the inside of the smallest gear and measure to the edge of the hole. Do this to both cranks, the difference in length, be it shorter or longer is your new spindle length requirement..
    – mikes
    Commented Dec 31, 2015 at 18:01
  • 1
    This, unfortunately, is an area where it's pretty much trial-and-error. Probably someone could come up with a scheme for accurately measuring a BB cartridge's properties, to know when one will exactly replace another, but no one has, to my knowledge. Especially, the relation between the length of the axle ends and the eventual positioning of the crank arm is fairly fuzzy, since the way the axle end snugs into the crank arm is a big determining factor. Commented Dec 31, 2015 at 23:55

1 Answer 1


No. And not only that, if you were to stay with square taper cranks you would find that the BB length for one crank does not necessarily match the BB length for another crank.

In other words, if you use a 103mm square spindle bottom bracket A with crank B, it does not mean you would use a 103mm bottom bracket C with crank D, regardless of whether bottom bracket C is square or octalink.

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