Bicycle Travel > Gear Talk

Drivetrain Advice

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jim:
I am in the process of building a touring bike and am looking for advice on the drivetrain. I want to use a 12-34 cassette with a XT derailleur, a mountain crankset, 22-32-44 or 26-36-48, and STI shifters. I am told a Dura-Ace or Ultegra front derailleur will not work on these chainrings and a XT front derailleur will not work with a STI shifter.  I have been told Shimano makes a Nexave front derailleur that will work but only on a 8 speed cassette. I would like to stay with a 9 speed. I thought about a bar end shifter for the front derailleur but would like to stay with the STI. Any advice or opinions would be appricated.
Thanks,
Jim

DaveB:
Not sure about Dura Ace but I'm pretty sure an Ultegra front derailleur will work fine with a 26-36-48 crankset.  My son had a Trek that came with an RSX crank with 26-36-46T chainrings and a 105 (same geometry as Ultegra) front derailleur.  It shifted fine with STI despite the small "big" ring.  

Also, I've modified a bunch of 8-speed and 9-speed Shimano road triple cranks from 30-42-52T to 26-42-52T and they also shift well with 105 or Ultegra front derailleurs even though the range exceeds Shimano's published recommendations.

The point of all of this is that the road front derailleurs are pretty tolerant of chainring sizes and total teeth. You should be fine.    

biker_james:
I changed the gearing on my Cannondale to get something better and went with 24/39/48. Shifts fine with a Tiagra derailleur and shifters. I have heard if you go to a 44 that the derailleur cage is the wrong curvature to work well. I would think the Nexave front derailleur would work whether it was meant for 8 or 9 speeds, but you may want to get a more experienced opinion on that one.

iSolo:
If you're going to spend that much money you might look into
a Rohloff 500/14 Speed hub. Gives the same gears as a
mountain bike but cost from $900 to $1200. I bought one two
years ago and won't go back to using derailluers. No
derailluer problems because I have none. I also put on a
Schlumph speed drive and have a gear inch from 14inches
to 124inches. If you're a weight weenie and worried about it,
the Rohloff will add an extra 1 and 1/2 pounds to the bike.
But you won't have to worry about breakdowns with this
thing. The Rohloff will also save you on chain wear. Besides
the worry free maintanence, being able to shift gears, and
multiple gears at a time, anytime, at a full stop at busy
intersection, or going up a steep hill or peddeling backwards,
is a new experience.

You really got try one before you start knocking it.
18,000 miles on the Rohloff, including the whole CDT and
from Montana to Florida, and 4200 on the Schlumph so far
without a breakdown, of any kind, and I have better gearing
than a mountian bike and road racing bike combined. Now if
I can just find tires that won't go flat.

Keith


DaveB:
Other than cost and weight, the Rohloff hub has two more disadvantages/problems:

1. The shifter is intended for straight bars and not suitable for drop bars.  I've heard of a couple of home made adapters to allow the use of drop bars but they were somewhat jury-rigged and required a fair bit of do-it-yourself construction.

2. The Rohloff hub requires horizontal dropouts to properly tension the chain, rather like a fixed gear or single speed setup.  If you get very lucky with your chainring/cog/chainstay length combination vertical dropouts can work but you can't be sure until you try it.  Rohloff does offer a chain tension device (sort of a stripped down rear derailleur) to allow vertical dropout use but that defeats some of the simplicity of the installation.

BTW, I just looked up the "Schlumpf speed drive" on Sheldon Brown's web site. My first thought was that it was one of his annual April 1 articles but apparently it's real.  What is also is is EXPENSIVE!  One of these plus the Rholoff hub totals over $1300.

The cost of a couple of chainrings and a derailleur or even a new crank is negligable in comparison.  

This message was edited by DaveB on 3-26-04 @ 2:46 PM

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