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Old 04-01-12, 05:05 PM   #1
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Front derailleur height

I looked at the 105 double service instructions and Shimano says to adjust the height of the front derailleur 1-3 mm above the large chainring. When reinstalling it after cleaning I set it at 1.7 mm which was much lower than from the factory. Is there a reason you'd install some at 3mm and others at 1mm? What are the tradeoffs? This is a compact 50-34 if it makes a difference.
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Old 04-01-12, 05:54 PM   #2
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I always set the derailleur as low as possible without having any interference; I set it so that a dime barely fits between the cage and the large chain ring teeth, which I reckon is about 1mm. Check the clearance at several chain ring positions as they are seldom perfectly round or centered. In general a lower derailleur setting will yield crisper shifting, IMO.
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Old 04-01-12, 06:22 PM   #3
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From experiance I have found that finding the perfect FD height can very a lot depending on crankset and gearing sometimes as low as a half mm up to about 4 above the big chain ring. Normaly I just find the lowest point at which everything works good and raise it just a bit. Your setting of 1.7mm sounds about right for most setups. If you found a hieght that everytning works great at with in reason I would just leave it and stop worrying.

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Old 04-01-12, 06:47 PM   #4
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i don't measure the gap but i set it low, under 2mm probably. sometimes the middle ring bumps into the fd on a triple so i have to raise it up
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Old 04-01-12, 06:50 PM   #5
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That 1-3 mm is a range, not a fixed value. Shimano is saying anywhere in that range (and perhaps a bit outside of it) will work best.
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