Originally Posted by legalize_it
a damping ratio is a unitless measure of a damped oscillation.
A ratio of
unitless measure? How could something be measured if there are no units to measure?
Originally Posted by legalize_it
when a wheel absorbs an impact/impulse, it ocsillates.
OK. How much does it oscillate? At what amplitude? At what frequency? For what duration? What mode do they oscillate... radially, laterally?
Originally Posted by legalize_it
a damped oscillation is a oscillation in which the amplitude decreases over time.
OK. So how long will any bicycle wheel, when it impacts a stationary object, oscillate. With the load of a bicyclist on it? And a compliant rubber tire between the rim and the ground?
Originally Posted by legalize_it
when a system with a high damping ratio receives an impulse the amplitude decreases over a longer amount of time than a system with a low damping ratio.
OK. In the case of a bicycle wheel, on a bicycle, with a rider, suspended by a pneumatic tire, how long will the twisted spoke wheel oscillate compared with, say a 3x laced wheel?
Originally Posted by legalize_it
citing gerd schraner from his book "the art of wheelbuilding" --
the twisting of spokes, instead of classic crossing work is a waste of time for road use. tests have shown that it results in a very unstable wheel. the lateral stability is about the same as a normally spoked wheel, but radially the wheel reacts so sluggishly that encounters with momentary radial overloads the highly praised damping effect is delayed. ... twisted spoking patterns are an additional mechanical disadvantage resulting from the extreme angle of the spoke directly at the nipple. (schraner, p. 60)
The twisted spoke thing gets tossed around usenet every once in a while, with some adherents anecdotally claiming it makes for a
stiffer wheel. And generally debunked by the likes of Jobst Brandt.
It seems for even the most oscillation prone wheel (and I'm not convinced that oscillation is at all a issue for
any reasonably built wheel), the very weight of a rider and damping of a air filled rubber tire would make oscillation a non issue. With all due respect to Schraner, the "highly praised damping effect" sounds like pseudoscience.