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Old 03-22-09, 02:22 PM   #1
doctor j
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New Project (?)

My current road bike, Ol' Fuj, is an 8-speed triple with 30/42/52 chainrings and a 12/28 cassette. The 30/28 combination gives me 27.9 gear inches.

I'm contemplating the acquisition of a new road ride which comes equipped as a triple with 30/39/50 chainrings and a 10-speed, 12/27 cassette. The 30/27 combination would give me 28.9 gear inches, a small increase. I would actually like to have a lower combination than the current 30/28, so I was thinking of replacing the 30-tooth chainring with a 26-tooth ring or a 24-tooth ring. I'd like to be able to spin up the steeper hills a little more easily. The 26/27 combination would give me 25.1 gear inches, and the 24/27 combination would give me 23.1 gear inches, around 17% better than I have, now. The new ride would come with a 105, long cage rear derailleur.

Has anyone replaced a 30t chainring with a smaller ring? Any problems with front derailleur and/or with shifting? Any other pitfalls?
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Old 03-22-09, 02:35 PM   #2
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I don't have any first hand experience so I honestly don't know.

What I know for sure is that STI triples can be touchy to set up. I have to assume that extending the chainring range is going to make that issue more difficult. Tandems commonly come from the factory with mountain bike cassettes and rear derailleurs. That's the direction I would investigate.
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Old 03-22-09, 02:40 PM   #3
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I'd recomend a rear derailleur change along with an 11/32 or 34 cassette. That's a pretty tall gear without fighting the front derailleur. That's not to say it can't be done, but its easier that way.
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Old 03-22-09, 02:46 PM   #4
Time for a change.
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I did for Ventoux- and I needed it. Changed the 30t to a 28 and the only problem I found was on the rear derailler. I only had a Sora R.D. which is not long reach. The Derailler cogs actually touched the Cassette when in 28/28 so against all that the beliefs that I have a problem- I took a couple of links out of the chain to tension the derailler more and it kept it away from the cassette. Could not engage 52/28 though as the chain was not long enough.

I am 10 speed and run a 12/27 cassette. The TCR now has a triple on it and before I go back to the mountains- I will be changing the granny to a 28 or possibly a 26. 28 will not be a problem as the 105 rear derailler will take it- but a 26 and I might have to shorten that chain to being too short again.

And front derailler changing was not affected with only the 2t difference.
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Old 03-22-09, 09:56 PM   #5
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It's like I have a twin.

My triple is a 52-39-26 with a 10 speed 12-27 cassette. Love it. It shifts fine. I really like the combinations of the 39/26. I seldom use the super grannies anymore, but they are there (maybe like Dumbo's feather) when I need them. My philosophy: One might as well have the widest range possible.
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Old 03-23-09, 12:49 AM   #6
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I went for a compact triple, 26/36/48 (corrected - I accidentally typed 46 for the big ring). When I expect a lot of serious climbing, I go with a 12-28 cassette. For less hilly terrain I get by fine with a 12-21. You could add more top end by going with an eleven tooth cog. 110 BCD is the answer for a versatile triple.

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Old 03-23-09, 08:17 AM   #7
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For a "Mountain Roadster" you might want to consider a Deore M532 crankset in a 26-36-48.

Sheldon Brown's website recommends an IRD Alpina derailleur for compacts, but I've been told that a Tiagra triple front D/R will work well with brifters. I can't comment about that. I have one of these on a bike with friction shifting and have another sitting on the shelf for future use.

This is the same chainring combo that is on my early 90's Trek 520 touring bike. My surgically altered and degenerating knees appreciate it. You can put on an XT rear D/R and swap rear cassettes easily.
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