Advertise on Bikeforums.net



User Tag List

Results 1 to 7 of 7
  1. #1
    Newbie
    Join Date
    Feb 2010
    Posts
    2
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)

    Changing out a double for a compact double or triple

    I am interested in buying a bike from a friend. The only thing holding me back is it has a Shimano 105 39/53T Chainring.

    I really need to minimally be using a 34/50 compact or a triple with a 30.

    My question is, what are the costs associated with changing that out? I assume that it would involve a change of the 105 front derailleur to go triple. Can I simple change out the rings and not the cranks if I go for the double?

    I know my friend will give me a deal, but I do need to consider the additional cost.

    Thanks!

    Richard

  2. #2
    Senior Member
    Join Date
    Nov 2008
    Posts
    74
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    you could just replace your chainrings, that would be your most cost effective option. you could also swap out the bikes' cassette for one that has a bigger cogs.

  3. #3
    DOS
    DOS is offline
    Senior Member DOS's Avatar
    Join Date
    Feb 2008
    Location
    Arlington, VA USA
    Posts
    1,232
    Mentioned
    1 Post(s)
    Tagged
    0 Thread(s)
    Quote Originally Posted by 24/7biker View Post
    you could just replace your chainrings, that would be your most cost effective option. you could also swap out the bikes' cassette for one that has a bigger cogs.
    Its hard to find rings smaller than 52 for standard 130 BCD crank which I would assume the OP'S 53/39 set up uses.(I think sugino makes some 50 rings for standard 130 BCD, but not sure on that); Triple 105 cranks (new or lightly used) can be had often for less than what two rings would cost. For example...

    http://cgi.ebay.com/Shimano-105-Trip...item35a70b75d2

    even comes with the BB.

    edited to add: Looks like FSA makes some small 130 BCD rings http://www.universalcycles.com/shopp...ls.php?id=5616
    Last edited by DOS; 02-21-10 at 08:06 PM.
    My Opinions > My Knowledge

  4. #4
    Senior Member
    Join Date
    May 2004
    Location
    Wilmington, DE
    My Bikes
    2003 Specialized Hardrock, 2004 LOOK KG386i, 2005 Iron Horse Warrior Expert, 2009 Pedal Force CX1
    Posts
    8,849
    Mentioned
    1 Post(s)
    Tagged
    0 Thread(s)
    A standard double crankset uses rings with a 130mm BCD which can accept a minimum 38 tooth chainring. In order to fit a smaller inner ring, compact cranks use a 110mm BCD.

    Your cheapest option for lower gearing is either a compact crankset (which will require only a new crankset and possibly bottom bracket) or a MTB cassette and rear derailler. The latter will give you wider spacing between shifts but retain better spacing between chainrings. The former is the reverse.

    Is the bike you are considering 9 or 10 speed? If 10 speed, the crank swap should be very easy as you won't need a new bottom bracket (assuming external bearings). If 9 speed, you'll likely want to swap out the Octalink bottom bracket for an external bearing BB to allow you to use the newer Shimano Hollowtech II cranks.

    Converting a triple would at a minimum involve a new crankset plus front and rear deraillers. Worst case, you'd need that plus a new left shifter and bottom bracket.

  5. #5
    Ovdabak, OR DArthurBrown's Avatar
    Join Date
    Feb 2009
    Location
    Oregon
    My Bikes
    2008 Mercier Corvus Steel, 2007 Trek 4300, ~1980 Takara Deluxe 12, 1985 Trek 620 (modernized)
    Posts
    494
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    Quote Originally Posted by richardtc View Post
    I am interested in buying a bike from a friend. The only thing holding me back is it has a Shimano 105 39/53T Chainring.

    I really need to minimally be using a 34/50 compact or a triple with a 30.

    My question is, what are the costs associated with changing that out? I assume that it would involve a change of the 105 front derailleur to go triple. Can I simple change out the rings and not the cranks if I go for the double?

    I know my friend will give me a deal, but I do need to consider the additional cost.

    Thanks!

    Richard
    The cost depends on your bike and what you are prepared to settle for. Ideally, you should use a triple with a triple front derailleur and a compact with a compact front derailleur. You can certainly get away without doing that, but shifting between the smaller two rings on a triple can be compromised if you use a double derailleur. Cranksets and chainrings are two of the most overpriced bike components, in my opinion. The more cost-effective solution is to get a new cassette or freewheel. Unless you live near pretty hefty hills, a 39/27 gear ratio is usually enough. A new cassette will run $25-65 depending on how many speeds it is. New cranksets are well over $50 unless you get lucky.

    That said, I live in Oregon and advocate for triples constantly. Too many of my friends avoid beautiful rides over hills because they saved a minimal amount of weight by going to a double.

  6. #6
    In beaurocratic limbo urbanknight's Avatar
    Join Date
    Mar 2006
    Location
    Los Angeles, CA
    My Bikes
    Specialized Allez, K2 Razorback
    Posts
    22,457
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    I swapped a standard double for a compact double. All that's needed is the new crankset, assuming you find one that uses the same interface (square taper, ISIS, Octalink, external, etc.). A standard front derailleur can usually be set up to work fine with a compact. Mine has been working for a few years now, and the worst was a dropped chain to let me know I needed to set the limit screw a little tighter.
    "Well, I guess you can cut the arts as much as you want... Sooner or later, these kids aren't going to have anything to read or write about." (Richard Dreyfus as Glenn Holland)

  7. #7
    Newbie
    Join Date
    Feb 2010
    Posts
    2
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    Thanks all! Not sure what I am going to do yet. I really don't want to rig anything that will just be OK. I would rather pass on the deal and by a set up that is specific for me. Thanks again!

    Richard

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •