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I ride a 2015 Cannondale CAADX (Sram Rival) which has an FSA Gossamer crankset fitted with 46/36 chainrings. It has 5 bolts and a 110mm BCD. I'm an old man with bad knees. I never ride on the 46 ring, but I could surely use a granny gear. Is it possible to swap my chainrings for a 36/28 pair, e.g., say a Vuelta SE Plus Chainrings 110mm BCD Black 36T and a Vuelta SE Plus Chainrings 74mm BCD Black 28T, or say these Sugino Chainrings? Is there any reason (beside aesthetics) that I couldn't move my current inner 36T chainring to the outer position? If the change is possible, do you recommend any particular chainrings to look at?

I realize that I will have to shorten the chain and possibly shift the front derailleur. Is there anything else that I need to be aware of? Thanks very much for any help!

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You’ll need a sub-compact (also called super-compat) crankset. With 110mm BCD the smallest chainring possible is 33 or 32 teeth.

There are sub-compact cranksets with 74mm BCD for the inner chainring and 110mm BCD for the outer chainring which should allow you to install something like 28/36. This Sugino OX2-901D Compact Plus+ for example. Looks like their smallest possible combination would be 24/34.

Keep in mind that a road bike front derailleur is not made for such small chainrings. Especially if you have a braze-on mount instead of a clamp for your front derailleur you could be limited in how far you can slide it down the seat tube.

Maybe a 33 teeth chainring combined with a 11–32 cassette would be good enough for you?

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  • Thanks for this answer, and for pointing me to the Sugino crankset. My front derailleur is a clamp on, so I should be able to move it down and supports up to a 16 tooth difference, so I think that should be okay.
    – Dr. Pain
    Commented Sep 4, 2019 at 11:16
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    @Dr.Pain its not only the position and tooth difference to be considered with the derailleur. They are curved to match expected tooth counts. There's a good chance it'll work, but don't be surprised if shift quality is horrible.
    – Andy P
    Commented Sep 4, 2019 at 12:00
  • Thanks Andy, I'll keep that in mind.
    – Dr. Pain
    Commented Sep 4, 2019 at 16:32
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On road cranks both large and small rings are generally fixed to the crank spider by the same bolts, and have the same BCD. A 110mm BCD crank will not be able to take much smaller than a 34 tooth ring. 74mm BCD rings just won't fit,

To get smaller rings you need a different crank. road sub-compact cranks with smaller rings than 46/30 do exist, but you may have to change your bottom bracket as well depending on the crank.

Mountain bike cranks offer smaller rings but are made for different chainlines and bottom bracket widths and can be problematic to fit to a road frame.

Some manufactures are now offering 'modular' cranks that may allow you to fit MTB size rings onto a road crank base.

If you bike has a braze-on front derailleur you may have trouble lowering it enough to work with really small rings.

There is a reason an inner 36 tooth ring won't work well in the outer position. The inner side of outer rings have ramps and pins that help the chain climb up when shifting from the inner to outer ring, these are obviously not present on the inner ring.

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  • Thank you for this answer, it was helpful. The 74mm BCD thing was just a confusion on my part because the Vuelta product listing for some reason says "will fit 110 BCD".
    – Dr. Pain
    Commented Sep 4, 2019 at 11:15

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