question is: will the 105 5800 RD be able to take a 34T cog? Remember that, on paper, 105 5800 is 32T max...
Originally Posted by
Slaninar
The shifting will work fine. It is the compatible cable pull ratio for shifters and RD.
However, the problem might be the chain wrap capacity of the RD. If you have more than one chainring up front.
Distance from the biggest rear sprocket can be tuned with turning the B screw all the way in, or reversing it if not enough (though it should work with just screwing it in).
Chain wrap capacity and how to "calculate" it is explained in detail here:
Rear derailleur
Look under: Derailleur capacity – cage length