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Question: What is my best bet for a crankset, given the following requirements for a road bike I am setting up:

  • 68mm "English" thread bottom bracket
  • Shimano STI "brifters", 2x10 (I already have these!)
  • Low crankset/chainring gearing approximately 24/39, similar to mountain 2x10
  • Front index shifting works reasonably well (between the two chainrings)
  • Other existing components are Ultegra 10-speed 12-23 cassette, Shimano 105 rear derailleur, and CX-70 front derailleur (all these parts should work with desired gearing)
  • Assume all current generation parts

One possibility I am considering is to use the Shimano 105 triple, and replace the outer ring with a guard; my only concern with this is that the spacing between inner and middle rings might not match what the 2x brifter is expecting. Various mountain cranks are possibilities, but issues with chainring spacing and chainline might come into play.

For my philosophy on this gearing, see this link at Rivendell Bikes: http://www.rivbike.com/Cranks-Chainrings-s/41.htm also click the link on that page for "low-wide" crankset.

Thanks!

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Double parts and Triple parts don't play well together - for example, a double FD is shaped differently than a triple FD. I also don't think you'll get a double brifter to play nice with a triple crankset without screwing around with some pulley. –  Batman Mar 27 at 17:08
    
one approach might just to be to swap out your cassette - I have an Ultegra 10sp cassette which goes up to 28 teeth I think. The only question would be whether the derailleur will interfere with the cassette. Do you think that might give you enough? It's quite a bit more than 23. –  PeteH Mar 27 at 19:00
    
Well, on most bikes, you can run a standard road double (or a smaller touring triple) in the front and swap the 105 RD for something like a long cage Deore derailleur and run a big cassette that way (a lot of touring bikes are specced this way). –  Batman Mar 27 at 19:43
    
they might be ok, depends on the current derailleur. I know Shimano derailleurs are rated for a maximum cog size - I think mine was rated for 27 teeth but I got away with 28. (Although both my parts were 10sp Ultegra the cassette was newer.) –  PeteH Mar 27 at 21:31
    
To Batman's first comment - the CX-70 is the cross bike front changer that works with STI. I chose it because it's shape fits better with the small and medium chainring. If I go with a triple crank I will replace the large ring with a guard. –  Old95rpm Mar 28 at 2:34
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