I’m hearing from a source I trust that using Shimano DuraAce DI2 makes sense with Shimano DuraAce chainrings, that using alternative chainrings might not be such a great idea, because the rings are flexible, and this can cause less than ideal shifting.
In particular, that impressive ZED-2 crankset on the Look 695 SR with the Look chainrings might not shift as well with DI2 as when using Shimano DuraAce chainrings. There are two reasons for this:
- Shimano chainrings are about as in-round as can be had; other brands can be out-of-round slightly (indeed, an SRM-modified crankset might not be as good as straight DuraAce).
- Shimano chainrings are ultra stiff. Other chainrings might flex under the high torque shifting of the Shimano DI2 electronic shifters.
Both of these factors can mean shifting performance below that of which Shimano DuraAce DI2 is capable. It just doesn’t make sense to me to invest in DI2 and then use other parts that might not function as well.
In addition, the way the derailleur attaches to the frame can also matter; the high torque of the DI2 shifting puts a lot of stress on the attachment point. So a good solid braze-on is fine (Trek and Look both do this), but other mounting approaches might not work as well.
I’m personally not willing to sacrifice any of the phenomenal DI2 shifting performance, so I’m sticking with Shimano parts.