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I would like to replace my existing MTB crankset with a GRX crankset to get a bigger outer chainring (cannot find anything for my existing crankset, FC-M4100-2).

Does that even work? I'm trying to read the manual but...

Ideas?

Alternatively, can I put on a bigger outer chainring on my FC-M4100-2 crankset. It's 26/36T and I would like to have 26/42T.

It's 96 bcd but I cannot find any rings. Any ideas? Is it even possible?

Editor's note: the OP's bike is a Specialized AWOL EVO, which is actually a road touring bike. It came with an FSA Gossamer crankset. The OP replaced it due to wear. Due to parts shortages, it was replaced with an M4100 (Deore 2x, 10s) crankset.

Update: Adding picture for feeling :)

AWOL Evo on summer trip

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The GRX FC-RX600-10 46/30 crank should go without issue on anything that came with the FSA 48-32 crank in question here.

It will work fine with your Apex FD presuming it's still in good condition.

I don't believe there's any compatibility between the SRAM road 10 FDs and your X7 left shifter beyond what can be fudged together. Ways you could address that with a flat bar:

  • Get SRAM flatbar road 2x10 shifters. That's really what should have gone on with the bar switch in this case.
  • Get just a left 2x SRAM flatbar road shifter and accept the mismatch.
  • Get a friction left thumbshifter or semi-indexed gripshift and accept the mismatch. This is the good bike nerd solution because it will work perfectly forever with whatever front shifting setup you want, which is useful for touring bikes in the era when other ways of doing it can run into compatibility problems so easily.

There's a lot to recommend the third option because there may come a day when you want to de-SRAM the bike completely, like when your X9 RD pivot bolt breaks or gets slopped out and you're faced with the decision on whether you really want to buy whatever legacy support SRAM 10 mountain RD is available at that point, and it wouldn't need to be changed if you decided to jump ship.

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  • Thanks a lot! Ill try with a GRX crankset then. Actually found one for instant delivery. Ill try and see if my current FD setup happens to work otherwise Ill go with friction shifting. For the FD at least.
    – Ola
    Sep 17 '21 at 6:22
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There would be a couple of potential problems if this were an MTB frame (NB: It's not; see comments & edit to original post). First, is your frame even compatible with a 46t big ring? MTB frames need to accommodate big tires. The way the chain stays are shaped for that purpose may preclude use of a 46t big ring. Wolf Tooth has a sizing guide that may help you see if this will be a problem.

Then, your Deore crankset has a chainline of 48.8mm. The chainline is how far the center of the two chainrings is from the frame’s centerline. The GRX cranks have a chainline of 47.0mm. Your MTB front derailleur might or might not travel far enough inwards. It’s impossible to say for sure without testing. The other issue is that the MTB front derailleur’s cage is going to be curved for small chainrings, and the GRX big ring is rather large. You might not get great front shifting. The back end of the derailleur might hit the ring if you set the overall FD height correctly.

Last, if you had an MTB originally, it might have been worth asking why you feel like you need a 46t big ring in the first place. If you’re on the sort of terrain where you frequently need that bearing, a gravel or touring bike might have been preferable in the first place.

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  • Thanks a lot. There is a long story behind it :) The bike (Specialized AWOL Evo) came with a FSA 32/48 crankset and BSA BB. The BB + crankset were worn out and I had to replace it quickly to be able to get to-and-from work and the Shimano FC-M4100 was what I could get hold of right there and then (used parts etc). So the GRX is actually a replacement for the FSA 32/48. And the 26/36T combo from the shimano is too light geared. Especially on the high end. On the low end it's actually better with 26 than 32 :) Any other recommendations based on this new info? :)
    – Ola
    Sep 16 '21 at 12:45
  • The FSA crankset seems to be optimized for OLD 135 and a chainline of 46,5mm so that's really close to the GRX?
    – Ola
    Sep 16 '21 at 12:58
  • FSA crankset: CK-OSC6023/86
    – Ola
    Sep 16 '21 at 12:59
  • @Ola I noticed that you have a road touring frame. The most recent version I could find appears to have SRAM Apex (road) shifters and at least a road FD. You should be able to straight up swap in the GRX crank. I am a bit less certain what to do about the BB, but it looks like the MTB BBs are compatible with both 68mm (that's what you have) and 73mm shells, so I think the BB can stay. I'm not clear if you changed the shifters and FD, because your title implies it, but there's nothing in your question.
    – Weiwen Ng
    Sep 16 '21 at 14:07
  • Thank you soo much! What should I do with the FD? Also go for a GRX FD? I saw that the GRX chainrings were mounted 2.5mm out?
    – Ola
    Sep 16 '21 at 18:02

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