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  1. #1
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    New 10-speed double build up, Limited Available Gear Combinations

    My problem is that I have limited gear selection on the small crankgear (34-tooth), as the chain starts to rub the outboard cage of the front derailleur, when I get to the four smaller cassette gears.

    If I adjust the FD to stop its rubbing, I find that the chain then rubs the inside face of the big crankgear (50). Due to this, it seems I only have six available speeds on the small crank gear.

    When I'm on the big crankgear, I can run on the 9-smaller gears with out issue, but get inboard cage rubs if I try to run the biggest rear gear when on the front.

    Yes, I know I'm not supposed to "cross-gear" in these ways, but that's a lot easier to swallow on my other bikes which are triples.

    This bike is being built from scratch - my first, and also my first "double". This is a Motobecane Le Champion SL frame, with 10-spd Ultegra cassette, Ultegra 6600 GS rear, and 6600 front derailleurs. The crankset is a SRAM Apex, 50/34, 110 BCD. Chain is 10-spd, 6600 as well.

    People talk about 10-speed gear trains as having 20-speeds, but in this case I wind up with only 15 usable combinations. In contrast, my 27-speed gear trains on my Specialized Sequoia, delivers closer to 25-speeds.

    What's the deal here on these 10-speed doubles?

    Thanks in advance!

  2. #2
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    Assume you are running Ultegra shifters? If so, there's a "trim" function on the low chainring, maybe the big as well. When in the low chainring and smaller cogs and you get rubbing, move the shift lever a half shift -- not enough to shift into the big ring, but you will feel a clicky detente and the noise will diminish. With the pinned and ramped big ring, you will get the chain rubbing on the big ring in the smallest cog, maybe even the second to smallest, but this is not the fault of the shifter or the derailleur. Likewise, if the shifter is adjusted correctly, there should be a half shift down from the big ring, so that when you're in a big-big combo, no rubbing on the front derailleur.

    If this is a bike you are building from scratch, and you have such questions as this, might be best to bring it to a shop for assembly.

  3. #3
    Gear Combo Guru Chris_W's Avatar
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    You could switch the large chainring to a 46 or 48 tooth version, or switch the inner ring to a 36 or 38 tooth. Other than that, you're out of luck - that is just the way it easy.

  4. #4
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    If it was mine I would change the inner chainring to a 36 and run a cassette that starts with a 13 or 12. Changing the big ring to a 46 or a 48 is also a good idea if the front derailleur can be lowered enough. Getting the derailleur low enough is often a problem for bikes with "braze-on" front derailleurs used on many modern road bikes. I had to modify the FD hanger on my wife's bike to get the FD low enough to work with a 49 big ring.

    You should also look into using a bottom bracket spacer to move the BB spindle out 2 mm. I'm not sure you can use a spacer on your particular bottom bracket. But if you can it will eliminate most or all of the chainrub on the side of the big ring. This type of spacer is usually easy to install.
    Last edited by Al1943; 07-01-11 at 03:52 PM.

  5. #5
    Low car diet JiveTurkey's Avatar
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    Set it up so that the 34T can reach all but the smallest cog. The 50T should only be used with the cogs that put you in the range above what the 34T can provide, with some overlap.
    Quote Originally Posted by slopvehicle View Post
    Not wearing a helmet makes me more aware of my surroundings. I find myself anticipating the hardness of concrete 50 or 100 feet in front of me, it's almost a zen-like connection between my face and the pavement.

  6. #6
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    Thank you mconlonx,

    If I try to correct this with trim on the left shifter, I belive the only way that would help is if the outside cage of the front derailleur were helping to guide the chain off of the big ring. But then I have the chain rubbing along the cage, which to me is not desireable. But this is a learning process.

    LBS? The fun in this is the challenge!!

  7. #7
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    Lowering the FD is no problem, because it's a clamp-on, Ultegra. The cassette range is 12 - 27 Ultegra. But if I can't keep the 34/50 compact, then I may have to switch to a triple (to move the chainline out). Yikes. I already have three bikes w/triples...

    I measured the chainline, and it's coming in almost perfectly at 45 mm. When I use a long straight-edge, from the outer face of the big crank, back to the cassette, the line intersects wtih the 4th sprocket. An ideally splint chainline would get me between my 5/6 sprockets, so I have already ordered spacer shims for the front BB.

    The other reason I'm looking to add spacers, is that when I back-pedal (on the repair stand), the chain will come off the big-crank, to the outside! This happends from the big-ring, on either of the two smaller sprockets.

    My rear wheel is perfectly spaced below my brake attachment, 130mm spacing; I have installed a new derailleur hanger, and the Ultegra 6600 RD is also new.

    I also checked the specifications for the Le Champion SL. The FSA compact crankset used the same 34/50 combination I'm using. Do you think there'd be any difference between the chainline spacing for a SRAM Apex, vs. the FSA that the bike shipped with?

    So I'm going to try a few more things before I bring this into my local shop.

    Thank you all for you input and comments,

    Terry

  8. #8
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    Thank you,

    Yes, I'll have to look at some kind of compromise tuning of these combinations - at least after I fix the issue with the chain coming off the big crankgear when I back-pedal.

    Thanks Again,

    Terry

  9. #9
    Low car diet JiveTurkey's Avatar
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    Quote Originally Posted by Terry_Zak View Post
    the issue with the chain coming off the big crankgear when I back-pedal.
    This is a symptom of cross-chaining. The fix is not using these combos. If you want a really easy fix that doesn't address the real problem: don't back pedal.
    Quote Originally Posted by slopvehicle View Post
    Not wearing a helmet makes me more aware of my surroundings. I find myself anticipating the hardness of concrete 50 or 100 feet in front of me, it's almost a zen-like connection between my face and the pavement.

  10. #10
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    Sorry for the confusion. This is not from cross-chaining. The chain comes off when I'm on the outer (larger) crankgear, and am on the outer two (two smallest) cassette gears. That is, the chain comes off the crankgear, when I back-pedal.

    Yes, I've read the older threads about "If this hurts..., don't do it." But on long rides I do back pedal a few times to help loosen up, and to drop my heel down to stretch my calve muscles.

    I also thought more about my post in the middle of the night, and relaized that I got one part bassackwards. The alignment of the outer crankgear intersects the 4th outermost cassette gear. Therefore by not intersecting the 5/6 gear, I'm already biased in a manner that should prevent the chain from coming off, when I back pedal.

    I checked some SRAM literature, and saw that for some of their cranksets the chain compatibility is Shimano or SRAM, but for others it states SRAM only. I thought a 10-spd chain is the same? Could the SRAM chain have more "alignment" flexibility than the Shimano?

    Thanks again JiveTurkey and others,

    Terry
    Last edited by Terry_Zak; 07-02-11 at 05:48 AM. Reason: inserted "comes off big crankgear" to 1st paragraph

  11. #11
    Low car diet JiveTurkey's Avatar
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    Hmm, so the chain is coming off of the outer chainring? Is it falling to the inside (onto the inner chainring) or to the outside (off the crank altogether)?
    Quote Originally Posted by slopvehicle View Post
    Not wearing a helmet makes me more aware of my surroundings. I find myself anticipating the hardness of concrete 50 or 100 feet in front of me, it's almost a zen-like connection between my face and the pavement.

  12. #12
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    Suggestion is that you go to your lbs and explain to them what you did and what you are trying to do and have them fix it.
    If that is not a option you want to use yet then do the following:
    - make sure that your front derailleur [ fd ] is set at the correct height in relation to your chainrings and that the cage is paralell to the chainrings
    - make sure that you have the derailleurs limit screws properly adjusted
    - make sure that cable tension on your fd is correct.
    Also check all of your adjustements on your rear derailleur [ limit screws, b tension screw and cable tension ].
    If you have everything set correctly it should all work ...
    The backpedalling issue to means that your fd or rd adjustments were a lil off OR that you are back pedalling fast.
    Good luck!

  13. #13
    Senior Member oldbobcat's Avatar
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    Quote Originally Posted by Terry_Zak View Post
    Sorry for the confusion. This is not from cross-chaining. The chain comes off when I'm on the outer (larger) crankgear, and am on the outer two (two smallest) cassette gears. That is, the chain comes off the crankgear, when I back-pedal.
    That would indicate something out of alignment with your rear, derailleur hanger or the cage may be bent. Have your local shop check these out.

    With compact cranks it's pretty normal to sacrifice the two or three outermost rear cogs when on the small ring. My advice is one cog, you're lucky, two or three cogs, welcome to the club, four, you may be able to get one back with a 1- or 2-mm spacer. But compact cranks, short chainstays, and 10-speed clusters are a difficult combination.
    Last edited by oldbobcat; 07-02-11 at 05:15 PM. Reason: Typos. I'm posting from poolside in Kona.

  14. #14
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    It's falling off to the "outside", right off the crank. And it happends within only 3/4 of a revolution, even if I backpedal very slowly.

  15. #15
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    Gentlemen,

    I thank you all again for help with this puzzle. I'll let you know what else I've checked, and the last thing I'll going to do; then I'll bring it to the shop.

    Other items checked:
    - FD height was set with the sticky-gauge, and alignment is parallel - all good there
    - Front and rear derailleur limits are all set properly
    - Chain tension (B-screw adj) is turned up
    - I also checked the crankset for parallelism to the wheel centerline; used a large square across the rear dropouts, and measured 1.2 inches to the left side of the outer crank gear, and the same 1.2 inches to the right side. Therefore the crank / BB / frame are properly aligned

    Recalling that the chain is coming off to the "outside" of the big crankgear, the last check I'll perform is derailleur alignment with the Park DAG-2 alignment gauge I just ordered. Even though the derailleur hanger is new, there's simply not many things left to check.

    Ah, one more item. I orignially was going to set this up as a triple, but then changed my thinking to a double. Because of this, I have the "long cage" rear derailleur; where I only need the short cage rear. All of the literature states that I should be able to use the long rear derailleur, but a shorter one would allow the chain to wrap around the bottom teeth of the outer chainring, just a little more?

    Anyway guys, I should know within a few days if the derailleur alignment makes any kind of difference; then it's off to the LBS. I already mentioned the odd-ball issue I'm having.

    Kind Regards,

    Terry

  16. #16
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    Update:

    It seems that oldbobcat was right on the money with this issue. I purchased a Park Tool, dérailleur alignment tool, and found that even though I had a new dérailleur hanger, the dérailleur needed some significant alignment changes.

    Now if I back-pedal, the chain will only come off the outside of the big crankgear (50-tooth) if I'm on my smallest sprocket. All others are fine.

    In addition, when I'm on the smaller crank gear (34-tooth), I can run on the inboard 9-sprockets, and only get some rubbing on the 10th when I have significant cross-chaining.

    So overall the problem has been fixed !!

    Thank you all for the help along the way,

    Terry

  17. #17
    Senior Member Ranger63's Avatar
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    It's all in the setup
    I've got the ultegra 6600 compact setup
    Initially had one shop do the setup and wound up with the same situation.
    Took it to Toms Pro Bike here in western new york and they dialed it right in so the single tap on the front allowed a full range use of gears.

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