Originally Posted by
Road Fan
So, a little more information may help:
The bike in question is my Terraferma 650b. It has a 28.6 mm seat tube and down tube. The rear is spaced 130 mm and I am using 10 speed gear gearing. I am looking to change it all over to Campagnolo 10-speed indexed with the Record triple. The crank is "modern," late '90s or at least pre-2010, in aluminum-colored aluminum. Chainrings have a dull finish - nickel plated? They are marked "10 speed". I've done a few crank fittings to this Terraferma and have always found that it's a challenge to get good clearance between the crank arm ends and their respective chain stays. I want the chainline to be correct with about a millimeter. I think I can measure it that well with consistency.
What it has now is a friction-shifted TA Cyclotourist double, 28/44 with a shimano 11/28 10s in the back. It shifts very well in the back with an Ultegra 10s chain. But I want to add a triple to get more gears that are usable. I'll probably go with a Campy 12/29, 12/30, or 13/29 in the rear after convert my hub to take Campy (it's a White Industries, they sell a conversion kit.) I have a problem with upshifting and over shifting. I can do it right with intense concentration, which means that setup is not MY best choice for centuries or longer rides. Hence I want to go to front indexing. Being a Campy Enthusiast, I'm taking this opportunity to Go to Campy on this bike.
My experience with Campy Record Triples (same one as this) installing one (with the Asymmetrical BB) on my Mondonico is that the installed clearance between the crank base inner edge and the BB shell can be small, such that I don't think a few mm offset is a good idea. On that great old Italian road bike, the crank arm clearances were not a problem. But those clearances will be much tighter on my Terraferma because it is designed for 650x42b.
That is my description of my situation.
I did not bother earlier as the information above I felt was needed to make any comment that would be useful.
It is the chain stay root width and divergence, overall width along the way that is really going to be your issue. Chainline may suffer to get the clearance for the inner ring and or the backside of the pedal bore.
There is a reason many modern bikes in plan view have concave chain stays.
If you have any Campagnolo period BB at your disposal, I would do a test fit. You may well need a longer overall spindle than you would like to clear the frame. Keep tabs on the chain line and note it, measure off the shell or seat tube to get your target overall lengths per side, and let the assembly advise you for certain.