There is also a huge gyroscopic effect on the main gear while retracting if wheels were still spinning.
The main gear is retracting sideways.
With spinning wheels , the "gyroscopic" force acts 90 degrees on this motion.
This would impose a torque on the strut which would damage the gear structure.
The nose gear is retracting "in-line" with the wheel spin direction (not sideways).
So this effect does not occur , and nose wheel braking is not neccessary before retraction cycle begins. (757)
Cheers
