Steve Maas writes;
I'm still waiting to see some hard data showing that (1) frames flex to a degree that is genuinely perceptible to a human, and (2) that there is a significant difference between any two frames of the same general type. This is especially unlikely in our case, since we are dealing with frames made of identical materials to virtually identical dimensions, for a given size.
I can understand an engineer's need for hard data. But I would ask why anyone would need hard data for an effect that is so easily observable? If someone were to insist that the light output of the sun varies with the number of sunspots, I'd say sure, show me some data, since the effect is probably too subtle for me to see. But I think I can trust my own simple observations to agree with someone who asserts that it gets darker during an eclipse.
My own simple observations over the last 35 years are thus: When I stomp hard on the pedals, the chain rubs the front derailleur cage, when I ease up it stops. SOMETHING has to be flexing. The fact that it happens more on one bike than on another when both bikes have the same model crank, BB, pedals, and chain makes it quite plain that at least some portion of the flex is coming from the frame. I'll concede that it may be difficult or impossible to tell any difference between frames of identical materials and geometry... but the effect is obvious on frames built with different gauge tubing or frames of different sizes (I don't think any capable engineer or physicist could dispute the fact that a larger frame is going to flex more than a small frame built of the same tubing).
I have never built a rig to test it, but it surely must be obvious to anyone who has ever climbed a hill at anything above a leisurely pace that a lightweight steel bike frame does flex.
Bob Hovey Columbus, GA
"You don't need a weatherman to know which way the wind blows" - Bob somebody or other