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I have a gravel bike with the following 1X set up:

  • FSA Omega Megaexo crank, 40T
  • Sunrace 11-46 CSMS8 cassette
  • Sram Apex1 11 spd derailleur
  • Sram Apex 11 speed Double-Tap shifter

I would like to change the cassette to an 11-51 but I don't think my derailleur can handle it. It is only rated for 42 tooth (even though it is working with the 46t I currently have).

Is there a derailleur that will work with this set up? What are the compatibility issues I need to consider?

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  • Hi and welcome to Bicycle.SE! Can you please edit your question to include what you've looked into already? Have you for example seen this article? Or did you maybe search with certain keywords but could not find anything? Please include that as well, it helps others to understand what you've tried so far. May 19 at 19:46
  • Usually, a rear derailleur can go a little beyond the limits in its specifications, however, based on your current setup, you appear (on paper) to be stretching it to its true limits, so you are correct in not thinking your Apex can handle an 11-51 cassette. If you are looking for some lower gearing, a smaller front chainring would get you there, but you obviously lose some of your highest gear there. Dropping your front ring to a 36 would net you a similar climbing gear as the 11-51 would (40:51 ~ 36:46). Your high gear would be like running in your 13 on the rear now (40:11 ~ 36:11).
    – Ted Hohl
    May 19 at 20:02
  • Thanks, yes I considered the lower front chain ring option but my crank wont' allow for anything smaller than the current 40 t so I would have to change cranks to go lower.
    – Markb
    May 19 at 21:39
  • I wish I could be more help. I am more versed in the Shimano side of things and what those options are. Good luck and welcome!
    – Ted Hohl
    May 20 at 6:16
  • If only it was possible to add gears on the front when there's no more space on the back... oh, wait... May 20 at 15:27

1 Answer 1

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Bikepacking has published an article on this subject. What you want to do is called a 'mullet' drivetrain (using a MTB derailleur with brifters). The basic problem is that pull-ratios on MTBs and road/gravel bikes don't match, so there's no 'factory way' of achieving this (speaking about mechanical derailleurs, it's possible with electric derailleurs, but that's another budget).

There's a configuration that can match your criteria: it involves a SRAM Eagle SX MTB derailleur, a Jtek ShiftMate 9 converter (that allows to use a SRAM MTB derailleur with SRAM brifters) and a Sunrace 11/51 cassette.

There is also another solution that is mentioned: buying a new cage for your current derailleur, from the Garbaruk brand.

Keep however in mind that these are "hacks" that may void the warranty. But the offer in gravel transmissions is quite limited, and except investing in an electronic transmission (super expensive), there's not so much that can currently be done.

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  • Thanks, that's very helpful. I looked at the Garbaruk products but I got the impression a different cage wouldn't help. i'll have to investigate that further
    – Markb
    May 19 at 21:45
  • Ok, it seems that this one garbaruk.com/… will do the trick. - Thanks again.
    – Markb
    May 19 at 22:01
  • Just keep in mind that you have to order the pulleys and the bolts separately. The cage is only the cage.
    – Renaud
    May 20 at 5:21
  • Checked with Garbaruk and they said i can use my current pulleys.
    – Markb
    May 31 at 21:16

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