This is also from the Used Bike Buyers Guide. Hope it comes out on your email with all the columns. Email me if you have questions. Lou Deeter, Orlando FL
SEAT TUBE ANGLE
Seat tube angle is the angle between the seat tube and top tube. Setback is the distance the seat tube is behind the bottom bracket, measured along the top tube. Setback will influence weight distribution, bike fit, and handling. With a normal frame, where the top tube is parallel to the ground, setback can be determined by dropping a string with a weight from the top tube so that it intersects the center of the bottom bracket. Measure along the top tube from the string to the center of the seat tube. To use the table, first measure the setback and seat tube, center to center, in centimeters. Find your frame size (seat tube measurement) on the left, then follow that line across into the table until you find the closest setback that matches your measurement. Now, go to the top and you will find the seat tube angle. If the setback measurement is between the numbers in the table, then the seat tube angle will fall between the two angles at the top. Record this measurement for a frame that fits really well. Then, in the future, when you shop for a frame, try to find one with a similar setback, given a specific frame size.
SEAT TUBE ANGLE (DEGREES)
70 71 72 73 74 75
76 77
S 48 16.4 15.6 14.8 14.0 13.2 12.4 11.6 10.8
E 49 16.8 16.0 15.1 14.3 13.5 12.7 11.9 11.0
A 50 17.1 16.3 15.5 14.6 13.8 12.9 12.1 11.2
T 51 17.4 16.6 15.8 14.9 14.1 13.2 12.3 11.5
52 17.8 16.9 16.1 15.2 14.3 13.5 12.6 11.7
T 53 18.1 17.3 16.4 15.5 14.6 13.7 12.8 11.9
U 54 18.5 17.6 16.7 15.8 14.9 14.0 13.1 12.1
B 55 18.8 17.9 17.0 16.1 15.2 14.2 13.3 12.4
E 56 19.2 18.2 17.3 16.4 15.4 14.5 13.5 12.6
57 19.5 18.6 17.6 16.7 15.7 14.8 13.8 12.8
I 58 19.8 18.9 17.9 17.0 16.0 15.0 14.0 13.0
N 59 20.2 19.2 18.2 17.2 16.3 15.3 14.3 13.3
60 20.5 19.5 18.5 17.5 16.5 15.5 14.5 13.5
C 61 20.9 19.9 18.9 17.8 16.8 15.8 14.8 13.7
M 62 21.2 20.2 19.2 18.1 17.1 16.0 15.0 13.9
63 21.5 20.5 19.5 18.4 17.4 16.3 15.2 14.2
SETBACK IN CENTIMETERS