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  1. #1
    Senior Member mtalinm's Avatar
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    Ok to convert standard compact double to 50/30?

    I'm on the Clyde side and find that a compact double doesn't get me up steep hills without mashing.

    As I'd prefer not to replace my crank and shifters to get a triple, I'm curious whether I could swap my 34 chainring for a 30. Bike is a Domane 4.5 with Ultegra drivetrain. Have already maxed out the cassette range with an 11-36 (only shifts up to the 32 though).

    Can't think of why it wouldn't work but maybe someone smarter than me will have words of caution...
    Trek Domane 4.5 (commute/distance), Specialized Roubaix (climber), Xootr Swift (winter/travel), Trek Soho (around town)

  2. #2
    Licensed Bike Geek Davet's Avatar
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    I don't think there's a front derailleur that could shift the chain from the 30t ring to the 50t ring, too big a difference.

    What you can do though, and has been done thousands of times, is to install a Shimano 9-speed MTB rear derailleur that is capable of being used with your 36t cog set. Then you'll be able to use all your gears. This is a fairly simple and easy thing to do.

  3. #3
    Senior Member mtalinm's Avatar
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    thank you for the excellent suggestion! in fact I have a MTB derailleur I can use for this purpose.
    Trek Domane 4.5 (commute/distance), Specialized Roubaix (climber), Xootr Swift (winter/travel), Trek Soho (around town)

  4. #4
    Andrew R Stewart Andrew R Stewart's Avatar
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    The big issue is that the compact crank is limited to a 34T small ring by it's 110mm bolt circle. If you look at the small ring and the bolts you'll see that there's no room for a smaller tooth count and still be able to bolt the ring.

    There's a reason that triple cranks exist. It just seems that the marketing departments have forgotten it. Or they wish to sell the sizzle of pretend dreams. Andy.

  5. #5
    Old fart JohnDThompson's Avatar
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    Quote Originally Posted by Andrew R Stewart View Post
    The big issue is that the compact crank is limited to a 34T small ring by it's 110mm bolt circle. If you look at the small ring and the bolts you'll see that there's no room for a smaller tooth count and still be able to bolt the ring.
    Where are the 86mm BCD cranks when you need them?

  6. #6
    Senior Member mtalinm's Avatar
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    Of course you're right, thanks!

    Quote Originally Posted by Andrew R Stewart View Post
    The big issue is that the compact crank is limited to a 34T small ring by it's 110mm bolt circle. If you look at the small ring and the bolts you'll see that there's no room for a smaller tooth count and still be able to bolt the ring.

    There's a reason that triple cranks exist. It just seems that the marketing departments have forgotten it. Or they wish to sell the sizzle of pretend dreams. Andy.
    Trek Domane 4.5 (commute/distance), Specialized Roubaix (climber), Xootr Swift (winter/travel), Trek Soho (around town)

  7. #7
    Senior Member Retro Grouch's Avatar
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    Regardless of whether it's do-able, I doubt you'd like it.

    The issue is "lack of overlap". With so little, if any, overlap between the two chainrings, as you climb a hill the gear combination mandates when you have to shift chainrings. As you make the multiple shift on the upgrade you'll lose all of your momentum.
    My greatest fear is all of my kids standing around my coffin and talking about "how sensible" dad was.

  8. #8
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    I believe that 33 is the smallest that will work with a 110BCD.

  9. #9
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    Quote Originally Posted by Andrew R Stewart View Post
    The big issue is that the compact crank is limited to a 34T small ring by it's 110mm bolt circle. If you look at the small ring and the bolts you'll see that there's no room for a smaller tooth count and still be able to bolt the ring.

    There's a reason that triple cranks exist. It just seems that the marketing departments have forgotten it. Or they wish to sell the sizzle of pretend dreams. Andy.
    Is it possible to set it up to use the smallest two chainrings of a triple crank, hence perhaps using 42-30 or similar?

    Thanks, Dick

  10. #10
    coprolite fietsbob's Avatar
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    Itwill work .. you need a variation on a 110-74 triple , using just the middle and inside chainring.

    I made a 144-86 triple into a 52-36 double , for hill climbing with old classic look components ,
    you drop into the granny at the bottom of the hill and upshift in the back ,
    then downshift as needed as you go Up .. only getting out of the little ring at the crest of the hill ..



    Velo Orange gets a TW factory to make a TA cyclotourist replica
    Grand Cru 50.4 BCD Crankset MK II - Cranksets - Components 50.4 mm BCD
    TA still makes their chainrings .. but dropped replacing the crank arms in production ..

    Compass Cycles has another (sub?) contract for his favorite French Crank to be copied in TW..
    Compass Bicycles: Cranks

    A Triple-izer inside chainring lets you screw a 74mm ring on a second set of bolt holes the ring it self has 10
    5 larger ones used to attach to the crankarm IRD (Merry Sales Imports) is the source.

    then you need a longer BB axle .. Hollowtech stuff is not going to work, Square taper will ..
    Last edited by fietsbob; 07-20-14 at 02:24 PM.

  11. #11
    Senior Member bikemig's Avatar
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    Quote Originally Posted by Andrew R Stewart View Post
    The big issue is that the compact crank is limited to a 34T small ring by it's 110mm bolt circle. If you look at the small ring and the bolts you'll see that there's no room for a smaller tooth count and still be able to bolt the ring.

    There's a reason that triple cranks exist. It just seems that the marketing departments have forgotten it. Or they wish to sell the sizzle of pretend dreams. Andy.
    + 1. The OP could also go for this crank sold by Velo Orange that comes stock with 46-30 chainrings (but it's a bit pricey):

    Grand Cru 50.4 BCD Crankset MK II - Cranksets - Components

  12. #12
    自転車整備士 oldskoolwrench's Avatar
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    If you're going to use just the inside and middle positions of a 74/110 triple, 74mm BCD chain rings are made in 30, 32 and 34 tooth sizes... then, a 30/50 could be made as you desire.

    https://www.google.com/search?q=74mm...ell=1&tbm=shop

  13. #13
    coprolite fietsbob's Avatar
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    Hollowtech Ultegra , why not just replace it with a triple crankset... then your low is 30t,

    3rd ring is just 4t less though.

  14. #14
    Senior Member mtalinm's Avatar
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    Quote Originally Posted by fietsbob View Post
    Hollowtech Ultegra , why not just replace it with a triple crankset... then your low is 30t,

    3rd ring is just 4t less though.
    then I need to buy a new shifter & crankset. had a Deore so here it is ready for the hills! thanks all for the great advice.

    wp_20140720_21_20_50_pro.jpg
    Trek Domane 4.5 (commute/distance), Specialized Roubaix (climber), Xootr Swift (winter/travel), Trek Soho (around town)

  15. #15
    Senior Member bikemig's Avatar
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    Quote Originally Posted by fietsbob View Post
    . . .

    Compass Cycles has another (sub?) contract for his favorite French Crank to be copied in TW..
    Compass Bicycles: Cranks

    . . .
    $435 for a double chainring crankset . . . . .

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