I just recently installed Q Rings both inner and outer chain rings on Shimano Ultegra 6800 groupset. The bike shifts perfectly when in the bike stand. But when I ride the bike, sometimes the chain falls when shifting from small to big chain ring. It falls towards the frame which seems odd. If it falls out to the pedal then I know I need to set the limit screws but this is different. It usually happens when chain in the rear cassette is in the 2 biggest rings. Any idea?

  • 1
    The high limit screw might be an issue, but have you changed the chain (new chainrings, you should)? Is it the same length? are the chainrings the same tooth count as before? – Chris H Apr 11 '17 at 13:49
  • It's a new chain and yes same length. – pinoy_ISF Apr 11 '17 at 15:08
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    Undershifting, you need to adjust the HI-screw on the FD. When you release the pressure on the lever, the FD moves a tiny bit inwards. – Carel Apr 11 '17 at 17:35
  • @carel flesh that out and you have an answer. Bikes in the stand aren't under the same pressures as when being ridden, and then problems get worse when wet. – Criggie Apr 12 '17 at 8:33
up vote 2 down vote accepted

Your front derailleur is 'undershifting', meaning that when you release the pressure on the lever, the FD moves a tiny bit inwards. This throws the chain off the big ring towards the small ring. If the chain is on a smaller rear sprocket you might notice that it is rubbing slightly against the outer plate of the FD.

You need to adjust the HI-screw on the FD. Give it a turn anti-clockwise and check if the chain stays on the ring.

As @Criggie justly points out, when a bike's settings are adjusted on a workstand things change a bit when it is ridden. Mainly due to the slight deformation of the frame when under the load of the rider.

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