Swapping compact for 52/39

chadders81
chadders81 Posts: 744
edited December 2012 in Workshop
I have bought myself a new bike for some big rides this year but it may also have to become my race bike this summer. It's specced with a compact and I suspect that I'll be grateful for it in the hills.

However, I gather I'll be better with a double for racing. I'm quite competent so easy enough to swap out the chainset for a proper double.

What I'm keen to know is whether I need to alter the position of the front mech?

Comments

  • AlanW
    AlanW Posts: 291
    Yes, you will need to move it up to allow for the larger diameter chain ring. Ideally you need to have about a 1mm gap between the tip of the chain ring teeth and the lowest edge of the mech.

    Once you have it set there, then you can swap between the compact and the std chain set without having to ever adjust it again.
    "You only need two tools: WD40 and duct tape. If it doesn't move and it should, use WD40. If it moves and it shouldn't, use duct tape"
  • Rich.H
    Rich.H Posts: 443
    You will need to check your chain is ok with the larger chain rings too. I have made this swap recently (53/39) and the existing chain was a couple of links too short for comfort. Rather safe than sorry

    Rich
  • AlanW
    AlanW Posts: 291
    Rich.H wrote:
    You will need to check your chain is ok with the larger chain rings too. I have made this swap recently (53/39) and the existing chain was a couple of links too short for comfort. Rather safe than sorry

    Rich

    Good point, this link should help HERE
    "You only need two tools: WD40 and duct tape. If it doesn't move and it should, use WD40. If it moves and it shouldn't, use duct tape"
  • gloomyandy
    gloomyandy Posts: 520
    Won't you need to lower the front mech when switching back to the compact chainset to maintain the correct 1mm spacing? Can you get away with the increase with some front mechs? My Sram front mech seems particularly sensitive to this gap and I suspect it would not be happy without being reset.
  • AlanW
    AlanW Posts: 291
    gloomyandy wrote:
    Won't you need to lower the front mech when switching back to the compact chainset to maintain the correct 1mm spacing? Can you get away with the increase with some front mechs? My Sram front mech seems particularly sensitive to this gap and I suspect it would not be happy without being reset.

    If you would have asked me that question a few months ago, then I would have said yes. However, since I have recently fitted a compact myself from a 52/39 chainset, I haven't lowered the front mech (Ultegra) and its shifts perfectly.

    And in truth the only reason I didn't lower it was that I was convinced that I wouldn't like the ratio combination of a compact. However, it turns out to have been one of the best mods I have done for many years. :oops:
    "You only need two tools: WD40 and duct tape. If it doesn't move and it should, use WD40. If it moves and it shouldn't, use duct tape"
  • Yossie
    Yossie Posts: 2,600
    I had to raise the front mech when doing this, no major bother. Obviously quick re-adjustment of mech required afterwards.

    The only thing to watch out for is that on some bikes by raising the rear mech you are reducing the clearance between tyre and mech so tyre rub occurs - easily solved by whacking on a smaller tyre ( I had to go from 25mm on teh winter bike to 23mm, so no problemo at all). I also Dremelled the back of the mech down for more clearance, but not really needed - just me being bored one night.

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