Bicycle Mechanics - triple to compact
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09-04-07, 10:51 PM
I humbly ask your advice. My crank arm is jacked up (long embarrassing story) and needs to be replaced and I found a good deal on a compact.
What parts would be required to switch from a triple to compact crank? What would have to be done to the front shifters?
The triple is the stock bontrager select and the compact is a shimano ultegra on a trek 1200. Everything is pretty much stock on the Trek.
What would make the most sense: order a new identical crank, replace with a compact, or replace the crank arm with spare parts from a LBS?
09-05-07, 06:29 AM
In order of increasing cost:
1. Replace only the damaged crank arm, particularly if it's the left crank arm.
2. Buy a new identical crank since you can use the existing bottom bracket and no changes to the shifters or front derailleur will be needed.
3. Change to a new compact cranks with the required bottom bracket and, possibly a new front derailleur.
Shifter compatibility will depend on the model shifters you have. 9-speed 105 and Ultegra STIs were both double and triple compatible. 10-speed 105 is both double and triple compatible but Ultegra is specific to one or the other. However, a triple STI can be used adequately with a double crank by locking out the granny ring with the fd's inner limit screw.
09-05-07, 06:46 AM
If you have an external bearing bottom bracket, you're good to go with just new cranks. If not you'll need to go with a new BB, 109.5 length (ie; if it's Octalink). Shifters are fine, ya might want to drop down the FD some.
Why would you replace with a compact? Do you really want worse gearing?
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