172 Driver and flyboymike, the question as I see it is why the bars drop back from 20° to 15°, not why they are sometimes 20° and other times 15°
Agree.. but still think that "FD commands MCP (normally V2) + 20 kts and the pitch command will be whatever it will be" gives the answer.
To the OP, the other week it was very windy over Europe. Climbing into a 40-50 kts headwind I think the airspeed quickly increased to close to 200 kts (with V2+ 20 being something like 160-170). You can imagine the FDs climbed through the ceiling and were of very little use. Once the wind stabilized and airplane "caught up" with the energy gain the FDs slowly came back to center. I never pitched above 20 deg ANU because my company doesn't like it.