Bicycle Mechanics - Ultegra triple crank -> DA triple crank ?
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11-30-05, 11:28 PM
I want to replace an Ultegra triple (9sp) crank (30-42-52) with a Dura Ace triple (9sp) crank (30-39-53). Can I do this without replacing the front derailer? The Shimano spec sheet on my FD lists 52 teeth as the maximum, but the DA crank is 53t. The FD is a band attachment so it could move up if required. Has anyone tried this? I'm wanting to swap to get 172.5 crankarm length and a 39t middle ring. Thanks for any info.
12-01-05, 12:18 AM
I wouldn't worry about the top gear difference -- it won't matter at all for a 1 tooth change. Just raise the derailleur a little bit. The problem you might have is with the middle.
I had a 52-42-30 crankset and swapped the middle ring with a 38, but ended up with lots of chain rub on the frout derailleur. This happens because the Ultegra 9-speed triple FD is shaped for a 10 tooth drop between the large and middle ring (this is a constant difference no matter how big the rings are). The derailleur narrows just below the level where there 42T middle ring would go, so when you put a smaller ring on there, it can rub a lot more easily.
Your best bet is probably to use a Dura-Ace 9-speed triple front derailleur, which is designed for 53-39-30. Ultegra 10-speed triple front derailleurs are also designed for 52-39-30, but the cage is narrower since the 10-speed chain is narrower, so you might still have chain rub problems. I got the Ultegra 10 triple derailleur and I have more chain rub than I used to, but it's OK since my front shifting isn't indexed.
Are you aware that Dura Ace 7703 cranks require special middle and small chainrings? For me, that would be a reason to not get it.
12-01-05, 11:36 AM
Winston, thanks for the info. Yes, I was aware of the DA special middle and small chainrings, but that didn't bother me since I was going to swap the entire crankset. Sounds like my best approach is to get another Ultegra 9 crankset off eBay with the 172.5 arms and just leave the 30-42-52 chainrings alone.
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