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Compact crank shifting woes

Last post 09-02-2017 12:58 PM by nickdodo. 20 replies.
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  • 04-26-2016 1:43 PM

    Compact crank shifting woes

    I wonder if anyone is having problems running a compact crank on their 2013+ R2/R3/R5?  I have a 2014 R5 on which I have installed a Rotor crankset and 50/34 Praxis chainrings.  Initially, I installed a 2013 SRAM RED gruppo, but because of what I thought was a buggy Yaw FD, I switched over to a Dura-Ace 7900 gruppo that I had lying around (with the aforementioned Rotor/Praxis setup).  The setup remains pretty unreliable, dropping the chain when shifting without pressure, so I tend to think that this must be a general problem, perhaps with older gruppos????  

     Any thoughts or advice

  • 04-26-2016 2:56 PM In reply to

    Re: Compact crank shifting woes

    I am not 100% sure of the answer I am about to give, but I believe if the chain is dropping, then it means the FD is not properly aligned. If it falls to the inside then the FD has to be moved outwards and vice versa if it falls off when going to the big ring. I run SRAM Red with a Rotor 3D+ crank and FSA chain rings on my s5 and the only times I have issue with the chain dropping are when the FD is out of alignment. Hope this helps or points you down the right path.
    Jens Voigt doesn't complain about what suffering does to him, but suffering constantly complains about getting picked on by Jens Voigt.
  • 04-26-2016 7:59 PM In reply to

    Re: Compact crank shifting woes

     The FDs have been adjusted and readjusted by an excellent mechanic.  Thanks for the thought though.

  • 04-26-2016 10:01 PM In reply to

    Re: Compact crank shifting woes

    First, in 2013 the R-series still had external cable routing along with a different under BB cable guide, which often generates some friction at the guide if not kept clean and/or somewhat lubricated.

    The 2014 R-series, to include the R2/R3/R5 are the ones with internal routing and use a different and improved under BB cable guide in my opinion.  I realize that some of these bikes, especially the R3/R5 may have been introduced in late 2013, but my main point is, the cable routing is something to consider.

    Second, which way does the chain drop? Off the small ring or off the outside of the big ring? Important to know since it points at FD adjustments/limit screws, but also at cable tension.

    If I'm not mistaken from reading your post... you simply swapped groupsets, and are not mixing, right?  If mixing Shimano/Sram, you have different cable pull ratios and also the fact that the Shimano shifters/FD has a trim level, while the Sram YAW FD does not... in any case, just throwing it out there.

    Outside of that, there are three things, which may be minor, but have some small impact on your issue... 1) housing/cable routing under the bar could be adding friction, hence loss of full cable pull/inconsistent pull  2) the Rotor crankset spider tabs paired with the Praxis rings may have created a slightly different spacing between rings which could be different than the spacing of Rotor rings or Sram rings (likely a non-factor, just throwing it out there) ...and 3) the FD braze could be slightly off in terms of alignment which will right away offset the geometry/movement of the FD and how it works with chairings.

    Perhaps you can expand on the actual situations under which you experience the chain being dropped and off which chainring... BTW, I don't think older groupsets are more or less susceptible to this issue.

     

  • 04-27-2016 9:44 AM In reply to

    Re: Compact crank shifting woes

    Sorry.  For some reason, I thought the 2013 was the start date of the latest iteration....I am talking about the latest, which sounds like 2014+ R-series.

    The chain drop is actually funny....I am trying to shift from the 34 to 50, and it actually drops IN about 1 out of every 5-6 shifts.

     Yes....I switched the entire gruppo.  No mixing.

     Thanks.

  • 04-27-2016 11:43 AM In reply to

    Re: Compact crank shifting woes

     I know this one may be way out there... but have you looked at the length of the chain?  Is it too long?  Shimano etc have a graphic of how the rear derailler cage should point down at about 90 deg when the chain is the correct length.  If the chain is too long and the rear derailler can not tension the chain enough then strange things might happen?  Does this happen in a particular rear sprocket more than another, ie if the rear is in a small sprocket? this might explain the irregularity?  Just random thoughts, I can not say I have ever seen something like this.  I find it weird why a chain can drop inwards when you are shifting the derailler outward, the only way I can see this happening is if the cage is too high and the chain is slipping under the cage inward.  I will be interested in the solution to this mystery.

     

  • 04-27-2016 11:47 AM In reply to

    Re: Compact crank shifting woes

    Also double check to make sure your chain rings are properly installed. Check that 1) the inner ring isn't flipped and 2) the index tabs for the inner and outer rings are properly aligned.

    2012 R3 SRAM Force 22, Kinlin XR31T rims on WI hubs, Rotor 3D+
  • 04-27-2016 10:09 PM In reply to

    Re: Compact crank shifting woes

    Thanks for all of the suggestions.  In truth, I would not have approached all of you on the forum if the fix was obvious.  Chain length is correct, chainring installation is correct, does not happen in a particular sprocket more than the other.  Mechanic that I work with is excellent.

    Yes.  Very weird that when I try to shift from 34 to 50 that the chain falls inwards.  With two different gruppos.  This is why I was wondering if anyone else had these problems (perhaps to do with the position of the FD hanger as it seems better suited for standard geometry since the FD attachment onto the hanger is low and for lack of a better word "incomplete," the geometry, or other weird quirks of Cervelos).  I have a 2006 R3, a 2008 SL-SLC, neither of which have this issue.  Just the 2014 R5.  And yes, I run compact on all of my setups.

  • 04-28-2016 9:53 AM In reply to

    Re: Compact crank shifting woes

    I'm not an expert, but maybe something to do/something is off with the trimming? Based on your description (trying to shift up but the chain drops inward) – is it possible that you shift up, but then the FD also trims (2 clicks instead of 1) so actually moves inwards a bit – dropping the chain back? If you replaced all the parts (from left shifter to FD to chain to chainrings) and nothing helps – could it be that the frame is out of spec? My 2 cents
    2009 S2, SRAM Rival, 50/34 Rotor Q-Rings, Mavic Cosmic Pro Carbons / Mavic Ksyrium SLs 7.2Kg
  • 04-28-2016 1:59 PM In reply to

    Re: Compact crank shifting woes

    WildeOne:
    I'm not an expert, but maybe something to do/something is off with the trimming? Based on your description (trying to shift up but the chain drops inward) – is it possible that you shift up, but then the FD also trims (2 clicks instead of 1) so actually moves inwards a bit – dropping the chain back? If you replaced all the parts (from left shifter to FD to chain to chainrings) and nothing helps – could it be that the frame is out of spec? My 2 cents
     

    SRAM YAW FD doesn't have/need trim, a very redeeming quality which was one of the reasons that convinced me update my groupo to it.

    OP, are the FD shifts that don't drop the chain "clean"? For example, does the chain tend to momentarily sit on the top of the chainring teeth during shifts before falling into the grooves like this:

    2012 R3 SRAM Force 22, Kinlin XR31T rims on WI hubs, Rotor 3D+
  • 04-28-2016 5:06 PM In reply to

    Re: Compact crank shifting woes

     the chain never makes it up.  just falls inward.

  • 04-28-2016 5:38 PM In reply to

    Re: Compact crank shifting woes

    I'd swear that would be a limit screw and/or cable tension issue, but we'll roll with you that it isn't. Other possible causes:

    1) Worn/bent/bad large chain ring- for whatever the reason the lifting pins maybe aren't doing their job. Have you tried a different set of chainrings?

    2) Weak/flexy FD hanger. The FD needs to firmly push the chain against the chainring lifting pins so that they can lift the chain up and over. If the hanger is too noodley that might not happen.

    2012 R3 SRAM Force 22, Kinlin XR31T rims on WI hubs, Rotor 3D+
  • 04-29-2016 9:04 AM In reply to

    • goodboyr
    • Top 10 Contributor
    • Joined on 08-16-2007
    • Thornhill, Ontario
    • Posts 950

    Re: Compact crank shifting woes

    +1 and pics would help.
    Bobbo
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  • 04-29-2016 9:48 AM In reply to

    Re: Compact crank shifting woes

     I have to say this is a physics problem for me, how can the chain fall inward when the derailler is pushing it outward?  That really perplexes me.  If the dropping inwards is truly a problem get a chain catcher so that it can not drop inward toward the BB and has to sit on the small ring regardless.... but for a mechanical system to drop the chain inwards is just plain strange.  A video of the problem occurring might help you solve it, get a slow motion camera so you can see what is happening. 

  • 04-29-2016 9:35 PM In reply to

    Re: Compact crank shifting woes

    i wonder if the fact that the FD does not mount completely onto the hanger is at least part of the issue.

     

     

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