I am having some difficulty using an older Serotta fit bike to obtain traditional stack and reach data. Basically, I am measuring to an arbitrary point on the adjustable headtube that I think would roughly be where the actual middle of the top of the headtube would be. There has got to be a better way. What is it?
Are you trying to determine the head-tube length relative to a specific stack height? You can measure from the floor to the head-tube; floor to bb spindle, and subtract the latter from the former. Other options are the Purely Custom X/Y tool or a jig.
I use the exit fit bike’s reference tool for this. Make sure the bike is level, put a level on the reference tool. Adjust the reference tool to the bikes stack and reach, mark the tool and measure.
best to take the X and Y to the handlebar clamp and then stick the front end you WOULD have stuck onto an exit or retul bike into THIS CALCULATOR. this will get you your stack and reach.