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I have a bike with a BB92 Bottom Bracket and would like some input on adjusting the front derailleur to consistently move the chain between the small and big chain rings.

Front derailleur is a top-pull, high mount, SRAM X9 for 2x10 speed that is cabled to SRAM XX Gripshift front shifter. Cable tension is as tight as I can manage for the wonky cable routing and limited space.

Crankset is a Rotor REX 3.2 with ovalized rings (38/26T). Both crank arms were spaced according to Rotor installation instructions and would be physically unable to move any closer inboard due to chainstay clearance concerns.

Chainline looks to be 60mm to the outer chain ring from the centerline of the BB shell.

When attempting to shift from small ring to big; I can apply light force to the inside of the derailleur to complete the shift.

If I don't apply light force; the derailleur will move the chain toward the big ring, but will then only drag across the ramping pins. It physically cannot move any further outboard enough to catch and pull the chain up onto the ring.

Big Chain ring to stay clearance

Chainline

Crankarm to chain stay clearance

Front Derailleur and Crankset

  • Have you adjusted the limit screws at all? Have you backed out the upper limit completely? – Paul H Sep 11 '19 at 19:49
  • Yes to both questions. – jc allen Sep 11 '19 at 20:11
  • The derailleur looks to be mounted too high. The norm is 1 -2 mm clearance between the big ring and the outboard side of the derailleur. – mikes Sep 11 '19 at 21:18
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    The derailleur is set that high to clear the ovalized chain ring when it's at its widest point from top>bottom. When the chain ring is rotated to that point, there is only about 2mm clearance between the derailleur outer cage and the tooth. – jc allen Sep 12 '19 at 12:06
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I don't have enough 'reputation' to add a comment, but +1 on 'mikes' comment about the derailleur being too high. If the derailleur is a bolt-on (hard to tell from pix), maybe the bike was designed for a larger big chainring?

Also, if the limit screws are all the all the way out, you might have to pre-load the derailleur travel a bit before tightening down the cable clamp.

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    You did the right thing. The answer field is for answering, I don't know why so many users feel the need to answer in comments even though the field explicitly tells to not do that. – ojs Sep 12 '19 at 5:32
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    The derailleur is set that high to clear the ovalized chain ring when it's at its widest point from top>bottom. When the chain ring is rotated to that point, there is only about 2mm clearance between the derailleur outer cage and the tooth. – jc allen Sep 12 '19 at 12:07
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    With the bike in a stand, and while slowly turning the cranks, can you physically pivot the derailleur further out and cause the shift to happen? If so, it seems like the issue might be that the shifter is not pulling up enough cable to cause the derailleur to move far enough. If, even by physically manipulating the derailleur, you cannot get it to shift, I'd question the compatibility of the derailleur with the crank. – toddg Sep 14 '19 at 3:41
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    I believe you're going down the right path with the cable pull-up Todd. I re-adjusted everything on the front derailleur yesterday (cage height, cable tension, rotation, and limit screws) I FINALLY got it to a point where it will, sort-of, shift in that; it takes a few rotations of the pedals for the chain to grab the ramping pins and move up onto the big ring. Dropping into the small ring is lightning quick though! I'm wondering if the Gripshift isn't pulling enough cable for the derailleur? – jc allen Sep 16 '19 at 15:05
  • Could be, but does it shift if you physically move the derailleur (by grabbing the derailleur and pivoting it using force -- not by pulling on the cable) to the limit while slowly turning the crank? If you can't make it shift while physically manipulating it, you're not ever going to make it shift by pulling the cable. – toddg Sep 17 '19 at 1:09
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+25

When a front derailleur is adjusted correctly but still won't lift the chain to the outer ring I have had success using a little creative bending.

With pliers, small channel lock, or a small adjustable wrench bend the front tip of the derailleur just a little bit and test, bend a little more if needed (Top View) in the drawing below.

Or, bend the bottom inside edge up just a little bit and test, bend a little more if needed (Front View in the drawing below).

The goal is to bend the derailleur in such a way as to compliment the lifting motion when shifting. Usually bending the front edge or the bottom front edge helps. Looking at the pictures you will want to focus the bend on the part of the derailleur doing the lifting - looks like the middle inside.

I lean toward the "bend as little as possible" school of thought but it's a judgement call on when to bend, where to bend, how much to bend, and if one should bend both the front and the bottom.

enter image description here

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  • Great feedback; thank you David. I’ll definitely give this a go. – jc allen Sep 19 '19 at 1:06
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The derailleur is too high. Also, you should not apply tension to the cable in the resting position beyond just keeping it tight, ie, don't force it tight through the clamp bolt, just pull it taught.

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    Derailleur is not too high -- it's an ovalized chainring (like the old biopace). When the crank is rotated to a position where the 'long edge' of the oval is in the direction of the derailleur, there's only a tiny gap. – toddg Sep 19 '19 at 12:33

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