Erik
Long-cage derailleurs are generally used only in conjunction with triple cranksets. However, I'll sometimes do an ultra-low gear conversion for a customer with a double and I use an actual MTB derailleur with their 12-32, or even an 11-34.
Your short-cage derailleur(shimano, sram, or campy) can typically handle up to a 28-tooth cog as long as you're using a double crank and your chain hasn't been cut too short.
-Erik
> From: mohair@aracnet.com
> To: obra@list.obra.org
> Date: Fri, 27 Jun 2008 17:32:26 -0700
> Subject: [OBRA Chat] derailleur question
>
> I'm rethinking my winter/rain bike setup and a 12-27 cogset with a 53-39
> ringset should work. The question is this: At what point do I need to go
> to a long-cage rear derailleur?
>
> To be thorough, I'll be using Shimano gear.
>
> Thanks.
>
>
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