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  1. #1
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    What chainring for cx50 crankset?

    I'm looking to knock the 36 tooth chain ring down to a 30 tooth chain ring, supposing that my short cage derailleur will still work and the FD will still work with the 30-46 combo. I have something like a 12-28 in the rear.

    What chain ring do I need?

  2. #2
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    The smallest ring you can fit on a compact road crankset is a 33t. You're out of luck unless you decide to put a triple on that bike. In that case, you would need a new shifter and rear derailleur, in addition to a new crankset.

    Another option, if you want, is to install a bigger 32t cassette and a compatible rear derailleur, along with a 33t chainring. That 33/32 low gear will give you nearly the same gear as the 30/28 that you're envisioning with your current cassette and a new chainring.
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  3. #3
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    Am I able to use a 12-30 tiagra cassette with a short cage rear derailleur and 36 to 46 double?

    Also, is there such a thing as a 10 speed specific hub that only certain 10 speed specific cassettes can fit on? How do you tell what type of hub you have?

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    A short cage may be able to handle that set-up. You have a total tooth difference of 28t and the Tiagra short cage can handle up to a 31t difference ((big cog - small cog)+(big chainring - small chainring)) so that part will work, but the biggest cog that a Tiagra short-cage derailleur can handle is a 27t. The derailleur may be able to squeeze under that cog, but if it doesn't you can use a longer screw on the B-knuckle.

    8/9/10 speed freehubs are all the same, so nearly any modern wheel that you can find will work with a 10-speed cassette. I don't remember off the top of my head which cassettes are narrower, but if you install the 10-speed cassette and it's still loose, put a small spacer behind it to tighten everything up.
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  5. #5
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    The short cage I have is a 105. Will that still work?

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    According to the Shimano website, yes. And it has a 28t max cog, which makes it a bit easier to stuff that 30t cog under it.
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  7. #7
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    I wonder what the hell they were thinking making a cog that big (30t) on a tiagra cassette when none of the derailleurs will work with it.

    I really need to go IGH. This shit is ridiculous. You'd think they'd have some sort of consistency to their systems, but no. It's like they're hell bent on making crap incompatible with other crap.

  8. #8
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    I'm really not sure what to tell you. A 30t big cog is approaching mountain-bike territory, and such low gears generally aren't necessary on a road bike. At low, yet comfortable cadence on my low gear of 39/27, on a hill that approaches 20% grade most of the time, I still maintain ~5-6 MPH. Any lower of a gear or cadence and it's easier and more efficient to walk.
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  9. #9
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    Then why have a granny at all? On a MTB or road bike?

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