Slowman wrote:
thank you. perhaps you can explain this, because i've asked it and i'm just not getting an answer that i make it thru my thick skull. reader error i'm sure. if the plastic innertube acts as a damper, measurably beyond what you'd find in a latex tube, why is it as fast? or faster actually than most latex tubes? do i misunderstand that the increase in a material's ability to act as a damper is analogous to the increase in hysteresis, then why - even on drums with proud features, especially on those drums - don't plastic tubes test measurably more poorly?Similarly to what others have already clarified, I was writing on the basis that, on average, a generic latex tube tests faster than a generic plastic tube. If two particular models test the same, then in this particular case, the two tubes should have the same "damping coefficient". This is what manufacturers of plastic inner tubes should be shooting for (or even targeting being faster than latex). Together with engineering the wall thickness appropriately, achieving this will come from their own recipe for polymer production and e.g. how it affects the interaction between the polymer chains (for instance this could be for creating more bonding cross-linking).
To continue de-conflating terminology, perhaps part of your original problem with the concepts comes from the perception of the two types of inner tube in the hand. Latex tubes are very flexible – not much force is needed to strain (i.e. "stretch") them by a certain amount. They are also very elastic (in the technical sense), in that they can be strained significantly before reaching a limit and suffering permanent damage or distortion. These two properties will make them feel "stretchy". I'm guessing that plastic tubes, in contrast, are both stiffer (more force needed for a certain strain) and cannot be strained as much before reaching a limit (less elastic). This will make them feel more rigid in the hand. However, while these contrasting properties can make a functional difference both to ease of installation and to the ability to conform to objects penetrating a tyre, they are not directly relevant to energy loss when riding. This instead derives from their respective "damping coefficients". Note that, given their very different stiffness and elasticity, likely this "damping coefficient" would be very hard to judge "in the hand". Indeed, the perception of their properties in the hand could be misleading, with what might seem like a logical conclusion from it being incorrect. This could be somewhat akin to the common misconception that increasing spoke tension makes for a stiffer wheel...