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Is "setback" a worthless dimension of geometry charts?(2 posts)

Is "setback" a worthless dimension of geometry charts?Fez
Jan 15, 2004 8:23 AM
Provided you get the seat tube angle, is the setback a worthless dimension?

http://www.gitabike.com/cgi-bin/shop/sc_loadpagez.cgi?user_id=15350&file=em_geometry.htm

True setback is ultimately dictated by saddle height, so isn't the only relevant dimension the seat tube angle?
not worthless...C-40
Jan 15, 2004 10:03 AM
Depends on your point of view. Most consumers are accustomed to the seat tube angle dimension, but traditional frame builders often build a frame with no angular dimensions at all. The seat tube is adjusted to a specific amount of setback and the front-center dimension is used to adjust the head tube angle.

Some brands will have odd fractional seat tube angles, because they are angles derived from the setback.

If a frame is designed as a series of lines representing the centerlines of the tubes, then the the cosine of the seat tube angle is the setback divided by the c-c seat tube length.

If you know that you want a certain c-c frame size, then the setback dimension can provide a valuable comparison of frame geometry.

You are correct that the total setback is determined by saddle height.