Is there a way to show the "effective" seat tube angle?
When you have a curved seat tube, the seat tube angle that is shown is the angle of the straight part above the curve.
Currently, as far as I know, the only way to show what the effective ST angle is is by adding an angle in manualy.
I understand that this "effective" ST angle will change with things like saddle height, however for visualization it would be great.
Yes, effective seat tube angle is available for display in BikeCAD Pro as described at: bikecad.ca/effective_seat_tube_angle
That goes through the center of the saddle and not through the clamp. I am looking for something that would go through where the saddle clamp would be on a non-setback post.
You are correct. If the saddle reference point is set to X=0mm and Y=0mm, then the effective seat tube angle will be measured through the top surface of the saddle where the rider would be assumed to sit (not necessarily the center of the saddle when measured front to back).
You can change this behaviour by adjusting the saddle reference point. In Figure 1 below, the Saddle reference point has been set as it often is with reference point X and Y both set to 0mm.
The top surface of the saddle is located with respect to the center of the saddle rails by dimensions P and Q.
In Figure 2 below, I've changed the Saddle reference point to align with the saddle clamp which I've located at the center of the rails. Since P=-10mm and Q=55mm, I set Saddle reference point (X) to 10mm and Saddle reference point (Y) to -55mm.
Be aware that changing the saddle reference point will change how most dimensions referencing the saddle will be displayed. If you prefer to design your frames around a particular position of the saddle clamp, you can explicitly define the position of the saddle clamp in X and Y coordinates with respect to the bottom bracket as described at: bikecad.ca/saddle_position.
Thanks a lot for the tip, While I undestand from a fitting standpoint what you are saying makes sense. From a purely visulization standpoint being able to show the effective seat tube angle is really important.
I trust from my explanation that you'll be able to show the effective seat tube angle for both fitting and visualization. Let me know if anything is still not clear or if you'd like to see any changes made to the program in this regard.
So can I just clarify please as an aside to this post. With regards reference point 'P' - Does a minus indicate the centre of the rails being behing the centre point of the saddle ie: towards the back of the saddle yes? So if the centre of the rails were in front of the centre of the saddle it would be +10 ?
Thanks.
No, a negative value for P would indicate that the centre point for the saddle is behind the centre of the rails. I can understand how you might have been a bit confused. In my example above, I used a value of plus 10mm for P. That was in an attempt to make my explanation as simple as possible. However, the default model that appears when BikeCAD is launched has a value of negative 10mm (-10mm) for P.
To summarize, if you want the saddle reference point to coincide with the center of the rails, you need to set Saddle reference point (X) equal to -P and Saddle reference point (Y) equal to -Q. P itself might be positive or negative just depending on the style of saddle.