Re: Suspension losses

On 1/2/2025 11:06 AM, AMuzi wrote:

On 1/2/2025 9:42 AM, bp@www.zefox.net wrote:

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

I think that would be true only if the smooth pavement were as smooth as a linoleum floor. Or a wooden track. IIRC, what got Jan Heine started on investigations of rolling resistance vs. tire width was coast-down tests on a Soapbox Derby track. I suspect that was quite smooth. Soapbox cars have hard tires and no suspension, AFAIK.

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.

I _may_ have been able to do such calculations 50 years ago, but I'm not sure. I certainly can't do them now.

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-)

I actually think physically modeling that dissipative blob might be valuable for the tire industry. Using such a blob to apply weight during a rolling drum test might give better information than what those tests give now.

 Clever.
 I take from that, you think the actual impact/height change/velocity change etc from various irregular surfaces can be quantified for any given random gravel (or road) experience and used to compare efficiency for other iterations.
 I hadn't thought of that, but if that's true then the rumble strip test isn't necessary for comparison. Which assumes sensors have adequate sensitivity across whatever range and that software for that data truly derives actual impedimenta values.

There are ways of quantifying roughness, with varying scales, varying tools. I'm most familiar with roughness measurement of machined parts, with tools varying from sample cards for "fingernail" test comparisons, to RMS readers akin to phonograph needles or laser scattering devices.
https://en.wikipedia.org/wiki/Surface_roughness
ISTR reading about systems for evaluating pavement fairly crudely, as in whether it should be repaved or not. I don't know of a system actually used for measuring pavement roughness at a scale affecting bike tire choice.
--
- Frank Krygowski