Seat tube sleeve

The option to make the seat tube discontinuous was initially introduced to enable the design of beam style bikes. However, in BikeCAD version 20.7, we can also use this option to represent a seat tube sleeve to reinforce the top tube and seat stay attachment points. The sleeve will be defined in the seat tube section of the tubing dialog box. We will use dimensions J,K,L and M to define the length and contour of the sleeve. If we only want a sleeve at the top of the seat tube, we can set dimensions K and M to zero. Meanwhile to add the actual seat tube, we will go to the Extra tube dialog box and add an extra tube. Where we define the attachment points of the tube, we'll find the option to choose BB in the second drop down menu. When we choose this option, the new tube will automatically inherit most of the dimensions defined in the seat tube section of the Tubing dialog box. The only things we need to define here are the seat tube diameter and optionally how much the seat tube may extend above the sleeve. If we choose to contour the top of the seat tube, and/ or add a pinch boss these treatments will be applied to this extra tube as well. If we reduce dimension DA and DB to zero, then both the seat tube and sleeve will receive the same top treatment.