HTupolev wrote:
Tom A. wrote:
By definition, equal displacement for same load results from equivalent stiffness, no?Read the Silca blog post I linked. Pressing arbitrary rigid objects against a tire is a more complex situation than pressing arbitrary rigid objects against a simple idealized spring: the shape of the contact area affects measured spring rate.
In the static case, Poertner's data suggests that small sharp deflectors have a spring rate that's dominated by PSI dependence, with only minor dependence on tire width. As the curvature of the deflector decreases, the spring rate becomes more and more width-dependent.
It's not obvious to me why a flat surface in static testing is a good proxy for sharper irregularities in the dynamic rolling case.
Probably because the "sharper irregularities" on the dynamic rolling case on typical pavement only really amount to extra flexing of the casing...think of it like an energy loss "bias" on top of what it would be for a perfectly smooth flat rolling case. As you pointed out, the "sharper" the object being pressed, the less the casing adds to the spring rate...in other words, deforming the casing at a more micro level only adds additional flexing losses, and not stiffness. Make sense?
HTupolev wrote:
Quote:
Obviously, any energy that can "make it through" the 1st S-M-D system is going to be dissipated in the 2nd, especially considering the relatively large amount of damping represented there. However, if you can keep the stiffness of the 1st S-M-D (i.e. the tire) low enough, then (with a quality tire) due to the low hysteresis losses, the majority of the energy put into the system by road roughness can be nearly completely returned at the contact patch. Pump the tires up too much and that energy then makes it into the 2nd SMD system, and is lost as heat. Hence, the "breakpoint pressure" which is observed in field testing.Yes. What I'm asking is, how much (and in what ways) does the damping coefficient of the second SMD system affect paved performance? By emphasizing the damping of the human rider versus something like an air spring, you're suggesting that it may have a significant impact. It would be interesting if that's been looked into deeper.
The air spring of a tire as basically zero damping...the vast majority of the damping losses of the 1st SMD is in the tire casing and tread. One could argue that the effect of the damping in the 2nd SMD system is demonstrated by the existence of the breakpoint pressure. Whereby, for a particular case of equipment, speed, and (possibly rider) increasing pressure results in dramatically increasing losses in the total system, i.e. once the stiffness of the 1st SMD is increased beyond a certain point.
I think some of smaller feature data in that Silca demonstration can be somewhat misinterpreted in regards to the scale of typical pavement roughness.
http://bikeblather.blogspot.com/