The rulebooks say not to do it, but I can tell you from experience that it works fine. Might be different with mechanical systems, but the power from a Di2 or eTap motor is more than sufficient to hoik it up a big jump like that.
It's not the cleanest shift in the world, but it does work.
48/28 double used to be Peter Knottley's recommendation for "cyclotourists" 40 years ago. It did actually work using a regular Record front mech — downtube friction shifters of course — but changes were leisurely.
The rulebooks say not to do it, but I can tell you from experience that it works fine. Might be different with mechanical systems, but the power from a Di2 or eTap motor is more than sufficient to hoik it up a big jump like that.
It's not the cleanest shift in the world, but it does work.