Originally Posted by fietsbob

having commonly used gear ratios requiring a double shift is a PIA..

So wide doubles, there needs to be a lot of overlap..

Benefit of a 42t in the middle is it spans the more commonly used ratios,
and its on the chainline center.

the 52 when you spin out the 13/42, the 30/19 for the lower range..

Not so much a parts swap, as using what you have, better.