BikeCAD Version 9.0 allows for the inclusion of a seatpost clamp, seatpost binder boss or wedge. To control this feature, click on the seatpost clamp icon in the top toolbar. The bolt on the seatpost clamp can be at the back as shown, or you could assign a positive value to X to flip the bolt to the front. To allow the body of the clamp to conform, we might take the overall length of the clamp which we can see in the B field is 43 mm and subtract from that the current value of A which is 18 mm to get a new value for A. At the same time, we can swap the values for R1 and R2.
Be aware that dimension C represents the thickness of flange on the seatpost clamp that rests above the seat tube. We can see this flange if we switch to the hidden line display mode and change the value of C to something larger like 3 mm. If we display the seat tube (C-T) measurement, we can see that this measurement is still taken from the BB to the top of the seat tube, not to the top of the seatpost clamp. Be sure to account for this if you wish your finished frame to have a specific measurement from the bottom bracket to the top of the seatpost clamp.
Besides, seatpost clamps, this dialog box also provides two styles of seatpost binder bosses available by clicking on the icons next to the seatpost clamp.
If we switch to an aero seat tube, we can also represent a seatpost wedge which are commonly seen on time trial bikes.