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Old 04-24-14, 01:44 PM   #1
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Front Derailleur Issues! 100k this weekend, please help!

I am struggling to get the Ultegra front derailleur to play nicely with a new Tiagra crank (it is a braze on FYI). When the derailleur is positioned so it only passes a couple mm above the largest chain ring, as it should, that it cannot move properly as it catches the middle chain ring. Then positioned so that it does not catch the middle chain ring the derailleur is very high, I can stick my index finger between the large chain ring and the bottom of the derailleur; even when slightly cross chained it loudly complains. This seems odd as I think the 50-39-30 sizing of the crank is typical of shimano triples and should therefore be fine to work with a triple derailleur.

I thought one solution would be to use a different derailleur, perhaps a Shimano CX-70 (praised as versatile here Trouble with STI Triples | Off The Beaten Path) that is meant for a double and would therefore not have the extra body of the triple derailleur and not catch the middle chain ring? Does anyone have experience with this or have another recommendation? There seem to be mixed opinions about if a double FD will work for a triple. Another problem is that when the derailleur is mounted flush to the braze on tab the arc is not correct (the arc is the correct shape but when mounted the rear is too low and front too high) and therefore I have had to put a little metal shim below the bolt to bring the rear of the derailleur up. Makes me wish I had a clamp style but I donít think there is any going back now (carbon frame FYI)?

More Background:

I am running a 3x10 Ultegra setup and recently started having issues with the chain skipping under load (it is about 8 years old). Not sure exactly how to describe it but the pedals would give underfoot a bit, it would feel choppy and sometimes the rear gear would change Ė especially when climbing, it was not acceptable to ride paceline with etc bc of this.

The cassette is relatively new and because the front crank had pretty severe shark teeth and chipping I replaced the crank and chain (cables and housings also replaced recently) thinking this would help the issue. It seems to have helped that particular issue and the rear is shifting beautifully. In an effort to save some dough I put a new Tiagra crank on the front; Shimano FC-4500 Tiagra Crankset Hollowtech II (Robot Check). Should I have any compatibility issues with this, it should be for a 10 speed no?
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Old 04-24-14, 02:08 PM   #2
Bill Kapaun
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What were the tooth counts of your previous crank?

I run a 22-32-36 on my hybrid, since emphysema prevents me from pushing higher gears anyway and I had to mount the FDER extremely high to clear the middle ring.
Shifting isn't "pristine", but it shifts to the large ring with a bit of over travel from the shift lever. (I usually just use the middle anyway)
It's UGLY!
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Old 04-24-14, 02:27 PM   #3
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The Ultegra triple crankset is 52-39-30 this probably account for the tuning.
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Old 04-24-14, 03:14 PM   #4
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Thanks for the input Bill, at least I know I have company out there on the road with bikes that have UGLY (as you put it) FD positions - because mine certainly is. I'm still hopeful there may be a solution which leaves it with cleaner shifts.

Lansing Wes, I will have to check the tooth count on the old Ultegra cranks but even so I would think that yes the FD may not work as previously positioned but should be able to be positioned to properly accommodate the new crank. I've come under the impression that the triple FD should work as long as the chain ring sizes have at least 10 teeth of difference between the middle and largest chain ring - which the new one does at 50-39-30.
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Old 04-24-14, 04:06 PM   #5
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As pointed out by LansingWes, the Ultegra triple front derailleur is designed to work best with a 13 tooth difference between the big ring and the middle ring. This means that the inside rail hangs down lower than it would for a 10 tooth difference. A 105 or Tiagra FD should fit better.
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Old 04-24-14, 04:29 PM   #6
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I used an Utegra triple FD (6603) in combination with a 105 triple crankset (50/39/30) for a period. That particular FD was designed with an optimum 13t difference between large and middle rings. (The "correct" 6603 crankset had 52/39/30 rings). I set the FD just high enough for the inner plate to clear the middle ring, and the outer plate did sit a bit high. While it was not ideal and was "out of spec" per Shimano, it did shift very well and very reliably.

I have no experience with the CX70 and didn't read the article, but I don't it as a solution for running a standard triple with STI. If you can't get the Ultegra FD to behave well with the 50/39/30 rings, then I'd look for a FD that matches your crank. Cranks in the 105 and Tiagra series have these ring combinations, so I'd look there for a FD as well. The contours on the inner plate will aid upshifts with STI; the CX70 lacks these contours.

It's not clear but it appears you resolved your rear skipping issue with the new cassette and subsequent chain replacement. It's usually recommended to install a new chain whenever you replace the cassette.
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