Rod,
My experience has been that more clearance is required for a double than a triple, due to the smaller size of the inner c-ring on most triples. A triple requires a BB spindle with more offset on the drive side. On a short-chainstay frame, this might result in unacceptable chain angle with some c-ring/cog combinations that would have been fine with a double. A more flexible chain might help mitigate this, but could then create shifting problems between the two smaller chainrings in the front. This might be addressable with a half-step + granny configuration on the front, or a different front mech. A Campy NR/SR front is at its max with most triple setups. Don't even try to use the rear, unless you have some kind of close-ratio setup (42-4x-53 serving 13-26).
Steve Barner, with five triples in Bolton, Vermont
>
> Date: Mon, 03 Mar 2003 14:52:19 +0000
> From: rodk3d@attbi.com
> To: classicrendezvous@bikelist.org
> Subject: [CR]difference in frames for double vs. triple crank
> Message-ID: <CATFOOD9FopYC98Bi89000000c6@catfood.nt.phred.org>
> Precedence: list
> Message: 16
>
> Hi all,
> What are the differences in a frame (if any) that have a double or triple
> crankset?
>
> Living here in Colorado along the "foothills", not being as young as I
used to
> be, blah blah blah, I find bikes with triples to be nice. They aren't
necessary
> for a lot of rides in the mountains, but when we hit em hard, it's either
a
> granny gear or walk!
>
> So, will most all frames work with a triple crank? Will the chainline be
ok?
> Does the chainstay need to be indented? Is there anything specific I
should
> look for in a frame that I intend to build up into a triple?
>
> thanks,
> Rod Kronenberg
> Fort Collins, CO