Originally Posted by
mstateglfr
Yeah, looks like I am piling on here- a 20t jump is massive and drivetrains arent designed for that. ....
My two derailleur touring bikes are half step plus granny, 46/42/24. If I got rid of the big ring, I would have a double with 42 and 24, an 18 tooth jump. And that shifts just fine.
I am using older derailleurs for a double, thus on the upshift off of the 24 I have to overshift and back off a hair, but that could probably be fixed if I had a derailleur that was designed for that instead of using a vintage one that does not lift the chain. I anticipated dropping chains, so I put a chain catcher on initially, thus I do not really know if I would have dropped chains or not, have not tried it without a chain catcher.
I do not think it would be any different if I had a 20 tooth difference instead of 18.
If I did get rid of the big ring, my derailleur would be closer to the granny sprocket, that would improve shifting from what I have.
ADDENDUM:
I should have noted that on these derailleur bikes, I use bar end shifters, Shimano BS-64, front is friction. For my odd mix of chainring sizes and derailleur choices, I am most certain that an indexed shifter would not work.