Does this look ok for a 11-32 cassette on a Shimano GS derailleur?

Discussion in 'Road Cycling' started by Edisonian, Sep 6, 2011.

  1. Edisonian

    Edisonian New Member

    Joined:
    Aug 17, 2010
    Messages:
    10
    Likes Received:
    0
    So after a bit of a debacle last year getting a LBS to upgrade my cassette to more teeth (which a lot of users here helped me though, thank you) -- I decided to do it myself.

    I bought a SRAM 9-speed 11-34 to try and replace my current Trek 1200's Ultegra 12-27.

    I knew I was reaching, but I read some people had some success with the 34t cog, even with the Shimano GS derailleur. One guy said as long as you don't shift to extremes, you should be ok.

    He was kind of right. I could get the pedals up to the 32t cog in the big chain ring (52t), but when I went to the 34, the whole drive train seized up. If I was moving, that could be *very scary.*

    So I've decided to trade the 11-34 for an 11-32 for that modicum of safety, so I don't seize up. The drivetrain seems to work ok with a 32t, on the big ring, but the derailleur is stretched.

    I wanted to get your guys' opinion on this. Do you think it's safe for me to put in an 11-32? Here's what it looks like:

    [​IMG]

    As long as I can turn the pedals, it should be ok, right?

    (And if you have time, I've posted another question about the cassette I removed to put in this 11-34. I wound up with an extra part -- I'm hoping someone can tell me what it is.)

    Thanks!
     
    Tags:


  2. oldbobcat

    oldbobcat Well-Known Member

    Joined:
    Aug 31, 2003
    Messages:
    3,233
    Likes Received:
    95
    This typically happens with a chain that's too short to handle the selected cogs, so you might be able to make this work with a longer chain. You'll need to sacrifice your small-small combinations, probably up to the second or third cogs on the outside, because of chain slap and the the chain rubbing over itself as it passes through the derailleur pulleys. Also, you might still get rumble as the chain passes between the guide pulley and your 34-tooth sprocket regardless of what you do to the b-screw (try inserting it backwards, but only after you've lengthened the chain.)

    When you push the limits of your components like this, seemingly insignificant factors--such as a half-centimeter of chainstay length, a quarter-centimeter of derailleur hanger length, a couple degrees of offset between the axle and the mounting hole of the derailleur hanger, or even the angle of the flat that the b-screw pushes against. There was a thread here a few months ago that might be helpful, about how to get the range of a triple without buying a triple. It was quite extensive and, in my opinion, sysiphian, but you might want to look it up.
     
  3. vspa

    vspa Active Member

    Joined:
    Jan 11, 2009
    Messages:
    2,203
    Likes Received:
    39
    yeah your chain needs to be extended, take it to the shop, they might have matching links for your chain,
     
  4. swampy1970

    swampy1970 Well-Known Member

    Joined:
    Feb 3, 2008
    Messages:
    10,057
    Likes Received:
    185
    That looks like an accident waiting to happen. Shimano GS rear mechs handle upto a 28 rear tooth although with a bit of adjustment of the b screw and luck with just having the right dropouts/gear hanger on the frame some folks can get a 30 tooth to work. The longer arm of the GS is designed to take up the slack on a bile with a road triple chainset with a road cassette, not a mountain bike cassette. To properly use an cassette with a 32 or 34 sprocket you'll need a SGS rear mech. As long as you don't get the latest 10 speed Shimano MTB a typical 9 speed SGS mech will index fine with road shifters, even with 10 speed 105/ultegra/dura ace. Make sure when you replace the chain that it's set up as per the Shimano instructions and set the b tension screw to get the top jockey wheel position set correctly to improve shifting.
     
  5. An old Guy

    An old Guy Member

    Joined:
    Feb 12, 2011
    Messages:
    1,380
    Likes Received:
    21
    Your drive train seized because the chain was to short.

    If the bike will shift to the 34 and everything turns, it will work. You just need a longer chain.

    ---

    I have a number of Shimano cassettes. With big cogs from 23 up to 30. They work with my short cage derailleurs (Campy and Shimano). I don't know if a 32 or a 34 will work with the models I have, but I don't have them so I don't need to care.
     
  6. alienator

    alienator Well-Known Member

    Joined:
    Jun 10, 2004
    Messages:
    12,596
    Likes Received:
    160
    The OP's picture is a perfect example of how an RD should never look.
     
  7. An old Guy

    An old Guy Member

    Joined:
    Feb 12, 2011
    Messages:
    1,380
    Likes Received:
    21
    There are 2 things to consider.

    First, the drive train is in the big/big combination. So that is as "bad" as it is going to get.

    Second, how much the derailleur can swing before there is damage. Mine can swing until the Derailleur almost hits the teeth on a 30tooth cog. That is much more than the swing shown.

    ---

    It does look as though that the chain is about as short as it could be and still function. That might be necessary to get enough slack out at the little/little combination. (My chain has almost 2 links of slack on the big/big combination. Not enough to let me take out the 2 links. But I am not so ambitious that I would want to take out the links. And I don't have enough slack on the little/little to worry about.)
     
  8. alienator

    alienator Well-Known Member

    Joined:
    Jun 10, 2004
    Messages:
    12,596
    Likes Received:
    160
    First, it does not appear from the enlarged picture that drivetrain is in the large-large. The chain is wrapped around the large cog at all.

    Uh-huh. Again: the RD in the picture..........it should never look like that. There are a lot of things that can be done but that shouldn't be done. You can remove all the brakes from your car except for the brake on the left rear wheel and possibly operate without harm. You could mount roadie wheels with 19mm tires on a inner and go mountain biking. The OP could leave his bike in that gear and glue his RD so that it can't move at it's pivots. These and many more things can be done. So?

    There are a host of advantages to setting up a bike correctly, some of which are not having the RD break early, not having the RD torn off its mount, not locking up the rear wheel and crashing.......

    There are things to learn from the picture, though: if your mechanic sets up your bike so that its RD does that, either find a new mechanic or learn to work on bikes properly yourself.
     
  9. An old Guy

    An old Guy Member

    Joined:
    Feb 12, 2011
    Messages:
    1,380
    Likes Received:
    21
    If you read the text, it appears that the photo is intended to show the position when on the big/big.

    If you want to believe that the photo shows the position when on the big chain ring and one of the small cogs, then the bike is going to have trouble with a 23 cog.

    Believe what you want.
     
Loading...
Loading...