Re: Suspension losses

AMuzi <am@yellowjersey.org> wrote:

 
I don't have a coherent argument either way but a rumble
strip test introduces a repeatable experience so that
various data may be compared.  Each rider on a dirt or
gravel path, and each ride experience by any given rider, is
an unique set of impedimenta such that data cannot be as
readily compared.

AMuzi <am@yellowjersey.org> wrote:

>
I don't have a coherent argument either way but a rumble
strip test introduces a repeatable experience so that
various data may be compared.  Each rider on a dirt or
gravel path, and each ride experience by any given rider, is
an unique set of impedimenta such that data cannot be as
readily compared.

But one can observe that in the case of smooth pavement,
suspension losses vanish, while hysteresis losses persist.

In the end a bike is an overdamped resonator excited by the
pavement and damped by hysteresis, separately in the tire and
suspenesion. In that limit, suspension would be faster if used
with very hard tires on very smooth surfaces. In the limit of
hard tires and no suspension, the dissipative element becomes
the rider whose elastic properties are apt to be poor, perhaps
accounting for the apparent slowness of solid tires.

Use of a rumble strip for testing is equivalent to selecting
a particular excitation spectrum. Choice of spectrum will affect
dissipation depending on internal resonances of the bike/rider
system. A real road likely corresponds to a 1/f spectrum, but
a rumble strip will likely be something else. How much difference
that makes isn't clear but it could be estimated using a mechanical
analogy equivalent circuit of the kind used to model loudspeakers.

A pair of series RLC circuits (one for the road-tire interface
and a second for the suspension-rider interface) would be a good
start. I'm not skilled enough to do the calculations, but others
on this group likely are. The hardest part is apt to be finding
an equivalent circuit for the rider, who isn't a rigid mass but
rather a dissipative blob....8-)

Thanks for reading,

bob prohaska