Thank you all for showing interest. It does motivate me to continue. @SJX426 asked about the difficulty of data collection. The answer is yes. One thing I discovered is that recording most of my commute generates LOTS of data which is tedious to sort through. But I do have a few ideas to enhance the result. Also my sweetie (Sharon) has gotten interested and wants to help, so tasks requiring more than two hands will be easier! In a previous computer-life I would have written a data analysis program but I'm not sure MSVC++ will run on my current machine. I've never mastered formulas in Excel but I guess this is as good a time as any.

So here is what I am "planing" to do. First I need to replicate the first experiments and check the math to make sure I didn't do stipud thingsome. Then I'd like to take measurements that can be related directly to bike behavior. For example, vary the tire pressure, measure some nearby bump(s) and try them on different bikes, compare HT (or stem) accelerations to axle accelerations, compare clinchers to sew-ups on the same bike, measure fork and frame oscillations while it is carrying my weight instead of unweighted.

A different set of measurements would be on the BB under various conditions. Not sure how I'd do that yet. An interesting result might be if BB resonance frequency is close to the fork/frame longitudinal frequency.

Several of you have raised good questions about differences in forks. [MENTION=65634]leftthread[/MENTION], regarding a straight fork, the geometry diagram shown in my initial post is valid regardless of the shape of the fork between HT and axle. Bump height still creates a thrust angle the same way. Zero rake would lessen the effect but not make it go away because the head angle still makes the contact patch be behind a line from axle to the bottom of the HT. What is different with fork shape is where or how it could flex. A conventional tapered fork would seem to have progressive stiffness, softer further down. So the effective flex point would seem to be lower than the HT, meaning the quasi-center of whatever arc the wheel can move in is lower and the fork itself would feel softer. A straight fork would seemingly bend mostly at the crown and force the frame to deform (and oscillate) in a shifting-trapezoidal mode, probably quite stiff. At the other extreme of thought experiment you can imagine a fork with an exaggerated S-shape bend between HT and axle, essentially a large spring. More length would give it a lower spring rate. The geometry of thrust angle would still be the same, but the wheel would not be as constrained to travel in an arc. Since I don't own a straight-fork bike I don't "plane" to check that.