|Shift quality question||Kurt H|
Sep 5, 2002 1:52 PM
|I've got a triple crank and derailleur set sitting around and am starting to plan for the next brevet season (only made the 200K this year 'cause I got married right in the middle of everything and spent many weeks off the bike...) and the possibility of a short tour. I'm wondering if I could set my bike up as a triple and, when not doing rides that MIGHT require the triple, just adjust the derailleur to lock out the granny and avoid overshifting problems. I wouldn't worry about mis-shifting during a brevet, but I'd hate to drop the chain or drop onto the granny by accident during a club ride. I'm thinking that if I lock out the granny, that the shifting would be similar to a double (all the way to one side or the other).
My understanding is that a lot of the shifting problems encountered with triples are on the front and involve either overshooting or undershooting the middle ring. Do triples add any shifting problems I'm not thinking of in the back? Does running a long cage derailleur with an 12-25 cassette (for example) lead to decreased crispness in shifting?
Oh, and FWIW, I'm not worried in the slightest about the extra weight of the cranks and the longer cage rear derailleur. The bike already weighs a ton, especially if I load up the panniers!
|re: Shift quality question||grzy|
Sep 5, 2002 2:28 PM
|While triples don't shift quite as nicely as a double - all of your concerns are stricly a function of drivetrain wear and setup. If your components are hammered or not setup correctly then you can be dropping chains and over shifting on your triple, but that would be the same as on a double - it just doesn't happen as soon. I've setup many triples for people and have totally dialed them in, but it takes time, skill and patience. No reason why the triple can't work flawlessly, but the tollerances are tight and the room for error is unforgiving. A tweaked bike or a single tweaked component and you'll drive yourself mad trying to make it right. Look for a mechanic who is a borderline perfectionist with possible obsessive personality traits - I'm serious. If s/he says they won't work on junk then you know you're getting close.|
|re: Shift quality question||Chen2|
Sep 6, 2002 6:21 AM
|The middle ring of the triple is typically a 42, the inner ring on a double is typically a 39. Something to think about when locking out the granny. I think it is unlikely that you would accidentally shift to the granny on a club ride. Most of the issues with shifting a triple are when shifting from the granny to the middle which is often a two step process, and the need for trimming due to the wider angles. Going from the big ring to the middle and back should not be a problem at all. I'm not aware of any shifting problems at the rear with a long cage derailleur or any unusual chain drop problems with a triple.
|39 vs. 42||Kurt H|
Sep 6, 2002 6:43 AM
|You know, I was having the same thought last night. If I go through with this and make a "most days double" out of a triple, I might end out swapping the 42 for a 39 to keep standard road gearing and give myself a broader range of gearing while keeping the rear cassette tight. That way I would have a 39X25 low without resorting to the granny instead of a 42X25. In addition I would have smaller shifts in between rear gears instead of the huge jumps on the 11-34 I have now. Then again, I've seen a lot of guys running doubles as 42-52 or 42-53 setups without complaining!|
|39 vs. 42||Chen2|
Sep 6, 2002 9:04 AM
|Kurt, the 39 ring from a double is not designed to run on a triple crank and shifting performance will probably suffer if you try it. The middle ring on a triple is ramped and pinned especially for use with triple rings. DT has a 39 that may work, but I have no knowledge of that. The Dura-Ace triple has a 39 middle ring that is specific to Dura-Ace and I've heard that it won't work with the other triples but I don't really know that. If you already have your triple crank-set I would go ahead and put it on and adjust it as best you can or get help from your favorite mechanic and go with it as is. As you probably know, the Shimano shifters for triples are the same as for doubles with the exception of Dura-Ace. If you have non D-A 9-speed Shimano shifters there will be an extra detent (click stop) on either side of the middle ring if they are set up according to specs.