Chain has fallen off the chain ring three times
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  1. #1
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    Chain has fallen off the chain ring three times

    Twice at the same intersection...

    I'm blessed in that I only have to cross traffic twice in a 40 mile stretch of bike trail I have access to but twice it has happened at the same intersection. I will usually go from 20mph to 5mph (or a complete stop, but I can't tell if cars are coming until the last couple seconds so I slow way down) or so and drop to the small chainring in the front so I don't have to drop 4-5 gears in the back and today the chain fell off for the 3rd time. I'm wondering what adjustment the bike needs... It's a 2012 Fuji Gran Fondo 2.0 (Ultegra front to back) with about 300 miles on it.

  2. #2
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    The fact the chain is dropping at the same intersection probably means you're engaging in the same behavior each time you approach that intersection. It's your actions, not the road, that need to be looked at. What exactly are you asking the bike to do? Pay attention to the gear combination that you're shifting to.

    In any case if your derailleur is throwing the chain when you shift from the big ring to the little ring your limit screw probably needs a small adjustment. Since I don't have the bike here in front of me I can't tell you how much of an adjustment may be needed, or if the problem is actually a loose crankarm (significantly less likely but can also cause this problem).

    Some mechanics mistakenly use cable tension to set the lower limit for the front derailleur. Mechanics who do this are also likely to skip the steps to properly seat cable housing. The end result is after a bit of riding the cable housing settles into the stops effectively (not actually) lengthening the shifter cable. If the limit screws aren't properly set this can result in your front derailleur over shifting to the small ring and under shifting to the big ring. If this combination of problems is showing up it means a minor adjustment to both the limit screw and cable tension. Again, these are likely to be minor adjustments, if this is indeed the problem at hand.

    That said, double checking to ensure the crankarm is properly tight at this juncture wouldn't be a bad idea.
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  3. #3
    tlg
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    I can say with 99.99999% certainty its your FD L-limit screw.
    Park Tool Co. » ParkTool Blog » Front Derailleur Adjustments

    It could also be your FD Rotational Angle, but you'd probably be noticing other problems if it were that.

    Go to the Park Tool site, check your FD Height, Rotation Angle, H & L limit screws. All pretty basic repair stuff that every cyclist should know.
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  4. #4
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    Remember in some cases, in the highest gear (53x11) the chain might rub the FD on some bicycles. Sometimes even if you have the smallest of clearance (say 1mm) it might still make the chain fall off when shifting.
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