Anyone have a formula to determine relative seat tube angle based on the nose of the saddle in relation to the BB? I assume it would also have to include saddle height.
You would only use the nose of the saddle if that’s where you ride. These measurements are typically made to the center of the seat surface, or the center of the seat rails.
You can use this for help: http://www.csgnetwork.com/righttricalc.html
Basically, you would measure in a straight line from the center of the BB to the measurement point on the seat and this would become the length of side ‘c’.
You would measure from the bottom bracket plumb line back to the measurement point on the seat (center or nose, whatever) and that would be side ‘a’.
Then calculate and you get the rest of the values plugged in. Angle 3 then is your seat angle.
sin (theta) = opposite/hypot
cos(theta) = adjacent/hypot
tan(theta ) = opposite/adjacent
Your hip is probably not in alignment with the front of the saddle though
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