Originally Posted by merlinextraligh

it's the K Edge derailleur cage mod for Di2 derailleurs.


We have one on a Dura Ace Di2 derailleur.


The K Edge Mod does 2 things: 1) it's a longer cage so it increases chain wrap, and 2) it moves the top pulley farther back to allow use with a larger big cog.


The Wolf Tooth, to my understanding just repositions the pulley. So it increases the maximums size cog you can use, but I don't think it has much, if any effect on how much chain it can wrap.


Many people on here have reported successfully running a 40 tooth rear cog with the K Edge conversion.


It may be that you your Ultegra derailleur, if you have the GS cage already has enough chain wrap to run a bigger rear cog, and you only need the Wolf tooth for the pulley positioning.


With the greater capacity of the current Ultegra Di2 RD, compared to the original Dura Ace, not sure there's as much need for the K edge conversion these days.