change triple crankset --> compact double

Discussion in 'Cycling Equipment' started by dannyyy, Nov 22, 2006.

  1. dannyyy

    dannyyy New Member

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    For abut half a year I've been riding a triple crankset. I'm getting sick and tired of triple's crosschain hell, so I thought I would change my crankset to a compact double.

    Instead of buying a whole new crankset, can I just buy the two compact chain rings and a new bottom bracket? I would be keeping my current crank arms.

    I think it would end up being much cheaper than buying the whole crankset (~$300), right?

    Thanks!
     
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  2. sogood

    sogood New Member

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    Cross chaining doesn't disappear with double does it? :eek:
     
  3. Strid

    Strid New Member

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    What brand and everything is your gear set? It's hard to tell you what to change, without knowing what you've got right now. :)

    Often, a triple vs. double has different front and rear derailleurs, different STI (left one) and of course different crank arms.
     
  4. Retro Grouch

    Retro Grouch New Member

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    Maybe, but it'll look goofy.

    You'll need a 50 tooth 130 BCD ring (for the middle position) and a 34 or 36 tooth 74 BCD ring. That second one might be hard to find. 130mm is too big of a bolt circle diameter to fit a 36 tooth chainring onto.
     
  5. dannyyy

    dannyyy New Member

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    i have a FSA Gossamer MegaExo Triple right now.

    I would be buying parts from the FSA Gossamer MegaExo Compact, so everything would be the same parts right? ...Since both are essentially the same thing other then the gears.
     
  6. 1id10t

    1id10t New Member

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    I could be wrong on this but compact cranks have a 110BCD. Your current setup would probably be 130/74BCD. FSA's site indicates their compact chainrings as having a 110BCD which won't fit your crank arms. I would think you'll have to buy new cranks but someone could correct me on this.
    Anyway, FWIW, I have compact cranks and quite like them. I find them sufficient for my needs. Also, despite recommendations, I found I did not need to change my front derailleur; I just moved it's position on the seat tube and it works very well.
     
  7. sogood

    sogood New Member

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    There are many models of FD and compatibility is model specific. So it's crucial for the OP to verify his/her setup.
     
  8. dannyyy

    dannyyy New Member

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    can you explain what BCD is? I'm not too familiar with that
     
  9. John M

    John M New Member

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    BCD= Bolt circle diameter (in millimeters) of the diameter of the circle that passes through all of the chainring bolts with the BB axle as the center of the circle. Standard double crankset BCD is 130mm for Shimano and most others, 135mm for Campagnolo. The outer two rings on Road triples are also 130mm (135 for Campy) with the inner ring of a triple being a 74mm BCD. As was mentioned the BCD for compact is 110mm. Therefore compact and standard chainrings are NOT interchangeable. Retro Grouch suggested an ugly way in which you could make your current crankset work as a 50/34 or 36 double.
     
  10. dannyyy

    dannyyy New Member

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    ohh. i see. so its probably too much trouble to switch out parts?

    i could buy the whole compact crank, but the price difference of switching and buying new is decent.
     
  11. 1id10t

    1id10t New Member

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    True. I should have clarified that it is not always necessary to change the front derailleur as suggested by some manufacturers (although Shimano does state their R700 doesn't require a derailleur change).
     
  12. lunar

    lunar New Member

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  13. alfeng

    alfeng Well-Known Member

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    BEFORE Campagnolo & FSA created Compact-specific front derailleurs, the front derailleur used with triple cranks was the common choice for cranks with wide/Alpine/compact chainrings; so, dannyyy is good-to-go with the existing front derailleur unless the additional grams of a "triple" front derailleur are a concern.

    Now, as far as cross-chain-hell described by the dannyyy with his/her triple, that is more of a consequence of lazy-shifting ...

    MOST of the time, I would think that the chain can simply be on the middle chainring if cross-chain-hell is a problem ... a rider should be able to handle ALL the rear cogs from the middle chainring.

    If the middle ring is a 39t, then simply change it to a 42t-or-larger -- a 42t chainring + EITHER an 11t OR a 12t cog is really a fairly high gear for most people under most situations.

    The granny can be reserved for when one needs lower gears ... OR, to bail-out onto if the drivetrain is underload and a lower gear is needed.

    The largest ring can be reserved for going DOWNHILL or just need to change your cadence for a mile-or-so.
     
  14. Rayzor

    Rayzor New Member

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    Most times you will need a different bottom bracket as well to get the correct alignment. Triple bottom brackets are usally longer.
     
  15. DMF

    DMF New Member

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    If you're sick of cross chaining, then LEARN TO SHIFT!




    Start by figuring out what gear you're in.
     
  16. dannyyy

    dannyyy New Member

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    i know how to shift... :confused:

    What kind of compact cranks do you recommend? Not too expensive
     
  17. Retro Grouch

    Retro Grouch New Member

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    I'd try to match the quality level of the rest of the components on your bike.

    I've had an FSA Energy crankset for a couple of years. I paid around $150.00 for it. I bought the octalink version and used my existing (double) bottom bracket and front derailleur so the crankset is the only thing that I had to buy.

    I like it fine. In fact, I think that it's the best equipment change I've ever made on my bike.

    You didn't ask but I think that how well you like a compact crankset depends on what gears you normally use on a flat road with no wind. My compact puts me in the big ring and right in the middle of my cassette. That gives me several "adjustment" gears in both directions without shifting chainrings. I generally reserve the small ring just for hills. If you find yourself right at the "cusp" of changing chainrings a lot you're going to hate the compact because of to the multiple shifts that are required to find the next gear in sequence.
     
  18. Alpha

    Alpha New Member

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  19. dannyyy

    dannyyy New Member

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    Its not JUST is the big ring/big cog, etc. There are plenty of other gears ratios that make that little grinding noise.

    I understand where youre coming from, but I just find it a hassle to shift several cogs every timei i want to shift just one ring
     
  20. sogood

    sogood New Member

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    Very odd. I have a triple (52 front and 12-25 rear)and couldn't hear grinding noises even on big-big (if I deliberately do that) except for FD rubs, and that's easy corrected with one or two trim clicks with the shifter.

    Maybe you need to re-examine your running gear's alignment, adjustments and lub.
     
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