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What’s Bottom Bracket offset and how do you decide what it should be?
It’s the vertical distance between the BB centre and the line joining the axles. Also known as BB drop.
Offset would be related to bottom bracket width rather than drop wouldn't it. Don't really understand the question though.
Designing a hardtail frame from Marino and it asks for the measurement for bb drop and separately bb offset.
I’ve said 45mm drop but left the other blank for now. I don’t know if it’s decide based on the chainstay length / seat tube angle / reach combined or something else. I wonder if it has a bearing on whether the seat tube is straight or has a bend in it - and can lead to the actual seat angle / virtual seat angle thing?
They have a diagram on the custom frame page.
It's how far forward/back the BB is from the seat tube centre.