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My bike has a FSA Comet 2x crankset, with 26t and 36t chainrings. The front derailleur is a Shimano SLX FD-M7025. Rear derailleur is Shimano XT (short cage, I think), and the cassette is 11-42t.
Can I just replace the 36t with a 38t chainring ?
I noticed FSA sells the 38t, but only as a match to the 24t and 28t chainrings, as seen here:
- 38t for 24t
- 38t for 28t
Can someone explain what is the difference between the above two chainrings ? Why couldn't I match the 38t to the 26t on my bike ?
Can someone explain what is the difference between the above two chainrings ?
The shifting ramps will be optimised to work with a certain inner ring.
I expect you could very safely replace the 36T with up to a 40T.
The shifting ramps will be optimised to work with a certain inner ring.
This. Each set therefore will have the pins/ramps/shorter teeth lined up to work together.
Any old chainring with the same BCD will work, but the inner ring will be designed to shed the chain at certain points and hold it at others so it might take more effort to shift it. The osymetric rings Ineos use for example don't have any ramps at all as they're custom made.
The only other (less likely) explanation is something like different BCD's, or thickness rings (steel vs alloy) meaning they won't line up with the spider or bolts wont tighten up.