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I replaced an FSA Mega EXO Crankset for a Shimano GRX FC-RX600 and SM-BBR60 bottom bracket. The reason I ask is that after installing the Shimano bottom bracket and crankset, I had to adjust the front derailleur out to align with the new chain rings. It seems the chain rings are 2 mm out from where the FSA were.

As far as I know, both BBs are for a 68mm shell. The Shimano installed fine in the frame, I had to use a different tool. The spindle length for the Shimano should also be identical to the FSA or so I thought.

With the new crankset in there, I am at the limits which is not good because I cannot adjust any more out. Not only that but I think that messed up the chain line as occasionally when shifting, it shifts as if the chain rings are worn (does not want to go from the small to the large chain ring).

Are they compatible or is this not installed properly or is something else going on?

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  • The design of the GRX spider means you could put a 1mm washer/spacer between the spider and the chainring at each bolt to bring the chainline back in.
    – Noise
    Commented Aug 7 at 7:21
  • NB the GRX front derailleur is designed for the increased chainline: are you using this part?
    – Noise
    Commented Aug 7 at 7:22
  • Yes, it is a GRX front derailleur, originally, it came with an FSA MegaExo BB and Crankset.
    – John Doe
    Commented Aug 7 at 11:24
  • I reached out to FSA and the GRX FC-RX600 has a different chainline than the MegaEXO. The FSA Gossamer is meant to match the GRX, but the Omega MegaEXO is narrower.
    – John Doe
    Commented Aug 7 at 16:34
  • If you have the GRX derailleur then the GRX cranks are correct and you need to set up the derailleur properly for your new crankset. There should be no compatability problem and be well within the derailleur's range of movement
    – Noise
    Commented Aug 7 at 17:28

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Performance road components have chainlines of 44-45mm. Shimano's GRX and SRAM's Wide cranksets have chainlines of 47-48mm.

On the 1x side, Shimano is probably quietly hoping that 1x drivetrains disappear overnight, but I believe their GRX cranks have a nearly 50mm chainline. Campy's Ekar has a chainline of 45.5mm, and SRAM's 1x cranks use 44.7mm.

Anyway, you put a GRX crankset with a gravel chainline on your road bike, which is expecting a standard road chainline.

I have no experience with this type of hybrid setup, but I've been told that a lot of time it works fine in terms of the FD, but sometimes it doesn't work. The symptom of not being able to consistently shift to the big ring is troubling. Switching to a GRX FD is likely to help.

You didn't ask, but I have said that Shimano needs to give us sub-compact cranksets with road chainlines. This is why.

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