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  1. #1
    mtbr member
    Join Date
    May 2005

    ...and again...Long, Medium, or Short Cage/Arm R.Der.?

    Seriously...I have an easier time finding jeans in my size that picking components for my bike.

    What are the benifits of either size cage/arm on a R.Der?

    Thanks Again!

  2. #2
    Inbred Homebrewer
    Reputation: Stick's Avatar
    Join Date
    Jan 2004
    Quote Originally Posted by dallas21
    Seriously...I have an easier time finding jeans in my size that picking components for my bike.

    What are the benifits of either size cage/arm on a R.Der?

    Thanks Again!
    Basically, shorter cages are lighter, stiffer, less prone to catching rocks, logs, etc (simply because they don't hang as low off the frame), and some might argue that they shift faster/better.

    The downside to a short(er) cage is that your gear (cassette and chainring) choices are somewhat more limited because the short cage derailleur simply cannot take up the slack.

    In other words, if you want to run the fairly common 3 x 9 setup 11-34 x 22/32/42(44)you've got to use a long cage. If, on the other hand, you're the racing type and you only run 2x9 11-28 x 34/44 you might be able to use a medium or short cage.

    The actual max gear difference you can run with a particular r. derailleur are listed in the manufacturer's specifications.
    "mmmm....Beeeeeeer." - Homer J. Simpson

  3. #3
    On MTBR hiatus :(
    Reputation: Speedub.Nate's Avatar
    Join Date
    Dec 2003
    Here's a little something to help you visualize what you're up against with a derailleur cage length choice.

    Shimano long cage derailleurs have a stated <i>capacity</i> of "45T". What this represents is the difference between your largest and smallest chainring, plus the difference between your largest and smallest cog. The formula looks like this:

    (Big Ring - Small Ring) + (Big Cog - Small Cog) = Capacity Req'd for a typical drivetrain...

    <b>(44T - 22T) + (34T - 11T)
    = (22T) + (23T)
    = <u>45T</u></b> you say <i>Great, I'll pick a long cage!</i>

    But like Stick writes, there are a lot of benefits to going with a <b>shorter cage</b>:
    <font color="blue">* higher ground clearance
    * better spoke/wheel clearance
    * higher chain tension
    * reduced chain slap
    * crisper shifting
    * LESS NOISE</font>

    ...and that above formula assumes you'll be using ALL your gear combinations, including the 'illegal' cross chain combinations (you know, small-small and big-big).

    In order to avoid ripping your drivetrain to pieces if you accidentally shift to Big Big, you always want to size your chain length accordingly. <i>But if you can stand the occassional dropped chain if you accidentally shift to small-small, read on.</i>

    Sticking with a long cage derailleur at this point will insure you can shift to any dang gear you like with no reprecussions, but you give up all the great benefits of shorter cage lengths.

    If you can accept that small-small combinations are unuseable, and can stand dropping the chain every now and then if you shift there, here's what happens when you install a GS (medium) caged Shimano derailleur on your bike:

    <img src="">
    <img src="">

    Shimano states a <i><b>33T capacity</b> for <u>medium cage</u> derailleurs</i>. Their stated capacities are a bit conservative, probably to allow for some chainstay growth due to suspension movement.

    The first chart maps an 11-34 cassette. The second maps an 11-32.

    The numbers are how much capacity is required in a particular gear combination. <font color="green"> The numbers in green are all within range of the GS cassette.</font>

    <font color="orange"> <b>The numbers in yellow are on the fringe -- just outside Shimano's stated capacity, but within the real range of the derailleur.</b></font>

    <font color="red"> The numbers in orange are unuseable. Shift here and the derailleur cage will fold back on itself, lose tension and likely drop the chain.</font>

    As you can see, the unuseable range all occurs in the small-small range of the cassette, where it wouldn't be a factor in day to day riding.

    You do want to factor in chainstay growth. This is pretty straightforward to measure by tying a piece of string around your bottom bracket's axle, then zip-tying it to the chainstay near the rear wheel skewer. Pull the string taut, then cycle the suspension, and watch the string to find the longest and shortest points. For every quarter inch of difference, plan on adding one half-inch long chain link, and add one to every number on the charts.

    You can see that choosing an 11-32T cassette gives you slightly more breathing room than the 34T option. Also, running a double-ring setup absolutely eliminates any excuse to run a long cage setup.

    Really, the quieter running medium cage is a huge difference, and is what kept me running this setup right up until I got rid of my derailleurs.

  4. #4
    mtbr member
    Join Date
    Apr 2005


    Speedub.Nate thanks for the info! Althought, I'm not the one who asked the question out loud, I always wondered what the difference was. Your post ranks in Top 5 most informative and descriptive (for me) that I've read on various forums here in the past 2 months!!

  5. #5
    mtbr member
    Join Date
    Aug 2004
    Amazing post...that was a great read i never really knew the difference etiher. Kudos

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