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Getting properly confused but I know its a simple answer for most. I have a brand new boost frame coming and will be building a boost wheelset but using my original non boost direct mount SRAM x01 cranks. I'm confused as to whether I will therefore need a 3mm or 6mm chainring to fit on to it (happy to grab a new chainring so dont want to know if my current ring will work). If boost moves it outwards surely I need a bigger offset chainring so the 6mm version but then I've done some googling and searching on here and now I think maybe I need a 3mm offset chainring as boost is 3mm and non boost is 6mm? Someone please help!
Boost frame, non boost cranks, what offset?
If your current chainring is direct mount, does it say 6mm on it? To move the chainline outwards by 3mm, you need a chainring with 3mm LESS offset from the chainset. So you need a 3mm offset chainring.
You may not even need the different offset, your current crank & ring may be fine. The only reason to switch would be for chainstay clearance
Ahhhh so the 3mm offset refers to 3mm LESS not MORE. The offset pushes it towards the bike then rather than away from the bike!
That’s exactly it Golfie. Boost moves the chainline out 3mm… but the offset of the SRAM chainring is in the opposite direction. And as the Honourable one says… it depends on the frame (and chainring size) whether the 3mm change in chainline is essential or not.