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Old 09-16-10, 03:22 PM   #1
djb
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Tiagra FD triple crank, what sort of teeth diff range can I go?

Hi, my new bike has a Tiagra fd, a 50-39-30 triple crank
Deore LX rd, 11-32 cassette. Specialized Tricross Sport.

While this gear range is fine for my needs, if I ever want to load this bike up and hit mountainous roads, I would like to bring the low gear down a bit. The present 30/32 is about a 25 gear inch, quite low but I had thought of perhaps if needed, putting on a 26 granny which would be in the 22 gear inch region.

Years ago, I changed my touring bike gearing from a 50-42-28 to a 50-40-24, which with the 13-30 cassette was appreciated on some of the tours I did when encountering really steep bits. The low became a 21-22 gear inch low. With the friction fd of the time, this was easy to do and worked without any problems.

Regarding the Tiagra fd and Tiagra brifters, what sort of issues are to be expected with changing the 30 granny to a 26? A fellow on this forum told me that he had this done for his Tricross by his LBS and it was straightforward.
It makes sense that being 4 teeth down means I might have to be a little more careful with not using the smaller teeth parts of the cassette (which I normally never do anyway) as the cage of the rd will potentially be closer up due to the extra slack.

Am I right in understanding that the main issue here is to know what the "teeth" range of the rear derailleur is?

I plead ignorance in this area, so if any of you are knowledgeable with this, comments would be appreciated.

thanks
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Old 09-16-10, 03:52 PM   #2
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Just go ahead and put a 24t small ring on it. The shift from the small ring to the middle won't be as slick, but it is easy to get used to. This will give you a real touring low gear. About 20 inches.
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Old 09-16-10, 04:12 PM   #3
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Triple front derailleurs can be picky about the difference between middle and large rings (yours is optimized for an 11 tooth difference) but the difference between middle and small is not so important. I would only put a 26-tooth on there to make the jump up/down to the 39 not too large. Plus, mount a chain retention device, like the N-Gear jumpstop, on the inside of the inner ring to prevent the chain from shifting too far and missing the inner ring when down-shifting.
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Old 09-16-10, 05:28 PM   #4
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thanks both of you, Yes, a 20-22 gear inch is nice to have. I recall in tight switchback in the Pyrenees, and some hills in San Fransisco on the West Coast trip, I was glad to have the 21ish gear inch. Most of the time, 25 gearinches is fine, but when a lower gear is there, it sure is nice.

As I said, I would only do this if I were to go loaded again, I have a crank puller so its really just finding a new granny (and yes, i would be inclined to go with a 26 myself) and allen keying to old one off and putting the new one on.

I have no prob putting on a cheap steel one, as the weight diff would be so little, they last a lot longer and they can be found quite cheaply.

Great suggestion on that N-Gear jumpstop, simple yet effective doo-hickey from the looks of it. Gruetsi. (my father in law is Swiss, and yes that is probably misspelled)
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Old 09-17-10, 12:19 AM   #5
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Originally Posted by djb View Post
Great suggestion on that N-Gear jumpstop, simple yet effective doo-hickey from the looks of it. Gruetsi. (my father in law is Swiss, and yes that is probably misspelled)
The Jumpstop is just one of several similar devices - there's also the Dog fang and Third Eye Chainwatcher, but I've found the Jumpstop to be the best (it's more sturdy).

I actually live in the French-speaking part of Switzerland, but thanks anyway. I'm sure your spelling is correct in one of the Swiss-German dialects, they all have their own variations.
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Old 09-17-10, 08:01 AM   #6
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alors, merci!
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