Nothing magical about 45 degree angle of bank. For any given angle of
bank, turn radius varies with the square of (true) airspeed. For the
gliders we are mostly used to and average sized and velocity gradient
thermals, 45 degrees is often about right. For a vintage type with a
stalling speed of 30 knots, circling at 30 degrees of bank, or even less,
at 35 knots may be better, for a heavily ballasted modern type, in a small
thermal, 60 degrees or even more may be best (better to dump the water
unless your pretty sure of finding bigger thermals later). How much bank
to use in a particular thermal is one of the most important and hardest
learned skills.

At 17:48 05 October 2013, son_of_flubber wrote:
I know that a 45 degree bank is useful for flying small circles and
staying
in small thermals, but is there something special about a 45 degree bank
compared to say a 50 degree bank?

For example, does the designer intend for the glider to do something
special at 45 degrees? Is the glider designed to balance aerodynamic
forces in a particular harmony at a precise 45 degree bank?