Originally Posted by
MikeOK
I have 6870 Di2 and have been very happy with it. However, I've always dropped the extra cash (within reason) for the latest and greatest. Compatibility is the only real problem I see with Di2, and for those who keep their bikes for 10 or more years it might be a challenge to find replacement parts.
What is shadow technology?
It is a a design tech they've been using on MTB RDs for years.
It moves the knuckles inboard of the dropout reducing the distance the RD sticks out. For mech derailleurs is also changes the cable routing
Some old MTB images for comparison:
