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  1. #1
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    SRAM Red Crank - Gap between drive crank arm and large cog

    Hello Bikers!

    So I'm doing a new build (don't do this often) with the following:
    - '18 Bianchi Infinitivo CV Disc
    - SRAM ETAP HRD Wifli
    - SRAM Red Crank BB30 (integrated spider/crank version)

    I am having issues where the bike shifts fine and works fine on my stand. However, I noticed that when riding, presumeably under load, that my drive side crank slightly rubs against the front derailleur when shifting onto the large cog. The contact points are the crank arm, and the adjustment screws for the upper/lower limit when the shifting to the larger cog, overshifts a bit before back a bit. Yes, this is standard operation on the FD.

    The presumptuous consumer in me says that SRAM thought about all of this in their engineering. Being 165lbs, I would hope that I'm not at the threshold of maximum weight.

    But I'm now curious. What are the gaps between the driver side crank arm and the large cog of other crank sets? When installed, my FD only has ~ 1-1.5 mm of clearance to the crank arm. Does anyone know if the Non-integrated SRAM Red Crank version has a larger clearance between the arm and cog? Anyone else experience this?

  2. #2
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    My current presumption, is that if I were to use the SRAM Red BB386 non integrated spider version of the crank, this would give me a longer spindle + force the use of spacers. this would increase the gap between the cogs and the FD. In this case, I have less of a chance of the derailleur hitting the crank arm.

    Can anyone else weigh in?

  3. #3
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    Quote Originally Posted by nitronikon View Post
    But I'm now curious. What are the gaps between the driver side crank arm and the large cog of other crank sets?
    1 cm for Shimano 6850 and 7950. That's as taken from the top of the teeth.
    Last edited by Jay Strongbow; 09-06-2018 at 11:01 AM.

  4. #4
    'brifter' is a lame word.
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    I just built a bike w/ that crank and etap. It's close but doesn't hit the arm when properly set up. Distance from the center of the large chainring (not cog) teeth to the crank arm is pretty much exactly 1.0cm.

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  5. #5
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    Thanks for the pic CXWrench. I find it interesting that the rub for me is the lower stop screws.

  6. #6
    'brifter' is a lame word.
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    Quote Originally Posted by nitronikon View Post
    Thanks for the pic CXWrench. I find it interesting that the rub for me is the lower stop screws.
    The crank is hitting the low limit screw?!?
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  7. #7
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    It seems so under load, especially when shifting outward onto the larger cog. You know how eTAP overshifts initially, then backs up a bit?

    When I compare my older bike with this new build, there seems to be more distance between the chain rings and the seat tube. This allows my shimano 105 FD to arch away from the tube, then down onto the chain ring area.

    For this build, the gap seems more narrow, and the FD seems like its reaching straight down almost. Therefore, less arch is observed. So when shifting outward, the tolerance/gap is quite minimal. For these reasons, I was considering switching to a SRAM Red crank with a non integrated crank/spider. the spindle is longer which will therefore force a larger gap, thereby creating a larger arch for the FD to reach out onto.

    I'll take pics when I get a chance to better illustrate.

  8. #8
    'brifter' is a lame word.
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    Quote Originally Posted by nitronikon View Post
    It seems so under load, especially when shifting outward onto the larger cog. You know how eTAP overshifts initially, then backs up a bit?

    When I compare my older bike with this new build, there seems to be more distance between the chain rings and the seat tube. This allows my shimano 105 FD to arch away from the tube, then down onto the chain ring area.

    For this build, the gap seems more narrow, and the FD seems like its reaching straight down almost. Therefore, less arch is observed. So when shifting outward, the tolerance/gap is quite minimal. For these reasons, I was considering switching to a SRAM Red crank with a non integrated crank/spider. the spindle is longer which will therefore force a larger gap, thereby creating a larger arch for the FD to reach out onto.

    I'll take pics when I get a chance to better illustrate.
    Sounds good, I'd like to see what's happening on your bike. The crank w/ the separate spider might do the trick in this case.
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  9. #9
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    Here's a pic. I've circled the 3 areas where I've notice it hit. The spacing here is 1-1.5mm. But note, that the concern is when the FD changes to the larger cog. In this specific scenario, it overshifts slightly, and that is when it hits. Right now I make sure to shift with the right leg down. But this is annoying..

    SRAM Red Crank - Gap between drive crank arm and large cog-img_2356.jpg

  10. #10
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    Quote Originally Posted by nitronikon View Post
    Here's a pic. I've circled the 3 areas where I've notice it hit. The spacing here is 1-1.5mm. But note, that the concern is when the FD changes to the larger cog. In this specific scenario, it overshifts slightly, and that is when it hits. Right now I make sure to shift with the right leg down. But this is annoying..
    You did the install correctly? Lined up the etched marks w/ the big ring? High limit is set correctly? Looks like there is enough room but it's really hard to be sure w/o seeing the bike.
    I work for some bike racers
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  11. #11
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    Yea.. I did the build, and brought the bike to an LBS, they checked it out and said its all good. I called SRAM earlier today. They said to get a spacer for the drive side, and reduce the adjustable shim on the non drive side. They said if that doesn't work, then I need to go the BB386/DZero route which has more length to play with. In addition, if we go the latter route, the cranks are more straight, less curved which should also give more space.

    I wish i knew this sooner. I would have gone straight to the non integrated crank/dzero but now the shop that sold me the cranks wont exchange them for me since its used.

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