FSA sells this which allows you to use BB386 cranks with BSA frames. Is the offset different enough between the two standards to cause problems with my chain line? I'm talking about the classic cartridge style BSA not the outboard BSA in case there is a difference. If there is a BB offset chart somewhere out there it would be super helpful as well.

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1 Answer 1


BSA or 'English' or ISO standard refers to the the thread in the bottom bracket shell (1.37in x 24 TPI). Both cartridge and external bearings fit in this these shell threads. There are several standards shell widths: 68mm for road bikes, 73mm or 83mm for mountain bikes.

There is no such thing as a bottom bracket chainline offset chart. Each bottom bracket standard has a specified external bearing width and internal bearing diameter. Cranks designed for a BB standard have the correct axle diameter and length for the bearings. The crank itself positions the chainrings for a specified chainline, not the bottom bracket.

You can read about BB standards here: https://www.bikeradar.com/advice/buyers-guides/the-complete-guide-to-bottom-bracket-standards/

The external bearing bottom bracket you reference will fit in a 68mm shell (you can see this in the specs on the web page) and provide the proper external bearing width of 86.5mm for BB385EVO. You need to check that your BB shell is the right width. You then need to check the specs of the crank to make sure it give you the proper chainline for the bike you are building up.

If you are building a road bike your BB shell will almost certainly will be 68mm, and a standard BB386EVO road crank will give proper chainline.

  • Thanks! I´m working on a road bike, so I should be set! This process has been very educational.
    – justin
    Commented May 15, 2020 at 16:20

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