Bottom Bracket Measurement

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  • I need to move my crank chainline out by 2mm (from 46mm to 48mm).

    I currently have a 113mm BB, so I was about to order a 115mm one. Then it suddenly occurred to me that this will only move the chainline by 1mm because chainline measurements only involve HALF the axle length.

    Am I right? To change the chainline by 2mm do I need to buy a 4mm bigger BB?

    Brain ache...

  • hmm makes sense!

  • Yes.

    Most current BB spindles are symmetrical, so to get 2mm on the drive side you'll need either a 4mm longer spindle or one with some offset (eg some older spec campag are 5mm longer on the drive side.

  • Thanks Guys. Looks like I'll need to go for a 118mm one then, which will give me an extra (118-113)/2 = 2.5mm which is exactly what I need :-)

    I wonder if the reality will match the theory. In theory, theory and reality are the same. In reality, they're not.

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Bottom Bracket Measurement

Posted by Avatar for Simon @Simon

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