Hi gang, At the risk of this turning into Bicycle Science, let me hopefully provide some clarification on the subject of losses when flexing a springy material. In the ideal world, a spring does not have any losses. In the real world, there ain't no such thing as "lossless" materials. Some are better than others, and there are some ways to get an indication of the amount of losses. Everyone is familiar with tuning forks, right? A two tined fork, usually used to tune musical instruments. When rapped, a tuning fork will vibrate for a long time, with the oscillations gradually decreasing. A perfect tuning fork would oscillate forever, but there are small losses every time the tines flex, which convert some of that potential/kinetic energy into thermal energy. The conversion of energy to heat is what causes the progressively smaller oscillations. My guess is that everyone on this list has rapped the top tube of a bike with a fingernail, and listened for a nice "ring". It doesn't take long to learn that a good steel frame will produce a nearly musical ring, while a cheap frame will produce more of a "thunk". What's the difference? The good steel has lower losses when it flexes, and will oscillate when struck. The cheap steel has a lot of losses, and this damps out the oscillations quickly. Why is a low loss steel frame more desirable than a lossy one? Other than the fact that it's probably lighter, of course... Seems odd that carbon fiber frames are famed for their ability to damp out vibrations, when that isn't considered a feature of cheap steel. It makes sense to me that there would be an optimal level of springiness in a frame. Most mechanical and elecrical power transfer systems work best with a load that has a matched resistance, as well as a matched dynamic impedance. In electrical power systems, a mis-matched load will result in the generator having to provide "imaginary power" (yep, that's the real term) which results in extra transmission losses. It's a shame that no one has done the research to nail down these factors better, and the manufacturers don't appear to think that the knowledge will help their sales enough to justify the expense. Until the research is done, we're left with little support for our beliefs beyond anecdotal evidence.
Steve "if you can't measure it, you can't improve it" Kurt Peoria, IL
From: Michael Kone <bikevint@tiac.net>
"Acutally this analysis is not correct - when the frame springs back all the energy that went to move the frame one way moves it back the other - and that movement is augmenting the pedal stroke - energy can't be wasted - it has to be conserved (i.e go somewhere and steel just doesn't dissapate a quanifiable amount of energy as heat from what I understand). Again, we do "waste energy" from extra body movement, but a frame cannot absorb energy in any relevent extent.
Many of the best riding quickest feeling bikes are very flexible - again, it is having the right flex that is important."