Can I use a 12-speed chain with 11-speed Di2? How about cranksets and chain rings?
Every now and then people ask whether they can use 12-speed chains with 11-speed cranksets, or use 11-speed cranksets or chain rings with 12-speed Di2, or the other way around.
Generally speaking, the answer is "yes" to all of these.
12-speed chain with 11-speed Di2 / cranksets
While the 12-speed chain is slightly narrower than an 11-speed chain, a 12-speed chain works just fine on 11-speed Di2 systems. The inner width is the same as that of an 11-speed chain, and the 12-speed chain will in fact run slightly quieter than the 11-speed chain.
You can use 12-speed chains with 11-speed Di2 derailleurs and 11-speed cranksets and chain rings.
11-speed cranksets on 12-speed bikes
Using a 12-speed chain on an 11-speed bike is not an issue, so can you also use an 11-speed crankset on a 12-speed bike? The answer is... it depends. In 9 out of 10 cases, this will work great. There is one thing to keep in mind though, and that is the difference in chain line.
The 12-speed chain line is 44.5mm and the 11-speed Di2 chain line is 43.5mm. In other words, twelve-speed front derailleurs expect the chain rings to be one millimeter further outboard. Usually no problem, as long as you can set up the outer and inner limits of the front derailleur properly - there's only a limited number of adjustments possible after all. On most frames this will not be a problem at all, but it is something to be aware of.
Using 12-speed cranksets on 11-speed bikes
Need to buy a new crankset, but don't want to invest in 11-speed parts? You can usually install a 12-speed crankset on an 11-speed bike with no problem. As mentioned above, the chain line is slightly different, but as long as you can adjust the front derailleur outboard enough.