Radius 1 will fit inside Radius 2, which will fit inside R3, which will sit inside R4
If you bought an Arc One set, its almost certainly all Radius 2.
Radius 2 comes in a "normal", which is 45deg, but is also available as a half piece 22.5deg, and a 90deg. 4 normal R2's will make a 180deg turn, width of that turn outside edge to outside edge will be 74cm
Radius 1, 4 pieces to make 180deg = 43cm across (also available are half r1 pieces, looks like a segment of pie)
Radius 2, 4 pieces to make 180deg = 74cm across
Radius 3, 8 pieces to make 180deg = 105cm across
Radius 4, 8 pieces to make 180deg = 136cm across