Hello, I'm wondering which measurements are most correct when it comes to cutting tubes lengths and applying the miter print outs. Do I need to be initially cutting the tubes to the center-center lengths? I had a bent seat tube and am using the Z1 and Z2 dimensions to measure from the center of the bb to the center of the bend. Then from bend center to seat coller. Same questions but with bent stays. I tried to vary the curvature to see if the length dimensions changed and it did not. I'm sure I'm overlooking something. I'm assuming from there I put the miter template paper on the tube and measure the miter-miter distance.
You can rest assured that all dimensions in BikeCAD are equally correct. I suppose the question is which dimensions are going to be the most useful for a given task. When using miter templates, I generally recommend using the miter to miter dimensions available in the Mitering tab of the dimensions dialog box. However, as you can see below, when you throw in a bend in the seat tube, these dimensions become a little more tricky to follow.
As you suggest, Z1 and Z2 could also be useful. To help you understand what dimensions change when the radius of the bend changes, I've created the following animated GIF.
Another builder recently requested that a line be added to the miter templates which could represent the intersection of the center of one tube with the center of the tube it is being mitered to. I'm working on adding this to the next update of BikeCAD. Perhaps it could be of some use in the bent seat tube case.