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I have a new bike and switched to a double (custom ) 50/39 from my old bike which is a triple. I am running a 12/27 in the rear. I am experiencing rub on the front derailer while in the 39 in my smallest rear gears 12/13/14/15. I have take this in to the LBS 2x and It hasn't been fixed. Since I am not use to riding a double is this normal? Or is it due to the 12/27 I am running in the back? I know I shouldn't be in the 50 and 27 or the 39 and 12 but what about the others? It seams as though my triple ultegra shifts better than my new double Dura Ace. Hmmm, any suggestions. Thanks
 

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after the front d, check this out

On my Giant OCR C the front d is adjusted properly, but when in the small ring on the front and the smallest cog in the rear, the chain is actually rubbing on the bottom of the large ring as the chain passes when pedaling.

I know this is a cross chained combo and not supposed to be ridden in, but still interesting to note the different noises and their origin.

I believe a slightly wider bb would fix this, but have decided simply to not ride in severely cross chained combos.
 

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Rub a dub dub

jnwarner0 said:
I appreciate the advice but the question wasn't should I pay or learn to do myself. I have not riden a double so do not know what to expect in regards to acceptable rub and gears.
Your derailluer shouldn't be rubbing the chain after you tweak the trim position. It is VERY common for the chain to rub the big chainring in the small-small combination, and not unusual to have that problem in the smallest two cogs. If your chain line is goofy, these problems can be worsened. A center line between the chain rings should hit the center of the cassette cogs. Sometimes the chainrings/crank are displaced toward the frame, making both chainring and derailleur rub problems difficult to deal with. Check your chain line first, and then look at that angle of the front derailleur cage - typically the outer cage should be parallel to the chain rings, though sometimes things work better with the cage turned out toward the rear just a bit.
 

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I don't think the chain should be rubbing on the side of the big ring since the rimgs are 39/50. This sounds like a simple derailleur adjustment, but there are other possibilities especially since it is a custom crankset.
Could one of the chainrings be reversed, more likely the inside ring.
Is the bottom bracket spindle the correct length? Check the chainline.
With my 1998 9-speed Dura-Ace I can use any ring and cog combination with no rub on the front derailleur and without trimming. And there's nothing special about my bike. I think you should be able to work the problem out.

Al
 
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