I've seen conflicting methods for determining chain length, for example:


Small cog to small ring:

https://www.youtube.com/watch?v=WnRxNHkRh8Q



Small cog to big ring:

https://www.youtube.com/watch?v=erL6Y6JFfnA


Big cog to big ring:

https://www.youtube.com/watch?v=OBv97hqqd0o


On SheldonBrown.com he promotes the big to big technique:

"The best technique for setting chain length is to thread the chain onto the large/large combination, without running it through the rear derailer. Mesh the two ends on to the large chainwheel so that one complete link (one inch, -- one inner and one outer half-link) overlaps. In almost all cases, this will give the optimum length."

Derailer Adjustment

So....

Which is correct, or better, and why?

Thank you.


P.S. This is for my road bike, double rings up front, 11-25 cassette, DA short cage RD.