Re: Suspension losses

Frank Krygowski <frkrygow@sbcglobal.net> wrote:

On 1/2/2025 12:06 PM, bp@www.zefox.net wrote:

AMuzi <am@yellowjersey.org> wrote:

 
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.
 

To a decent approximation, yes. Any surface profile can be represented
by a spectrum. Music is usually represented by "pink" noise, thermal
noise is white (uniform) and most real systems have noise proportional
to 1/f (imagine turn-on transients as singularities). A real road would
likely be some combination with the radius of the tire serving as a high
frequency filter.
 

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.

 
One would have to measure the force/deflection curves for both tires
and suspension elements, along with the masses of the sprung and unsprung
elements. Since losses are rate dependent, especially for suspensions
with hydraulic damping, a range of speeds/frequencies would have to be
measured. I think an accurate model would get fairly complicated, especially
if the rider were included. Each compliance (tire, suspension spring, seat
spring and rider body part that deflects) would have to be accounted for.
 
There are potentially four coupled resonators: Tires, swingarm/forks and
finally rider (divided into arms/torso sections probably). Overall, tests
on a rumble strip or drum with some kind of ergometer might be simpler.
 
Very likely the motor racing industry already has software that can do the
analysis. Most of the interest in that market is controlling resonances,
not minimizing losses, but otherwise the problems are very similar.

 
One further thought: If we accept (as I do) that jiggling the human
pedaler does cause loss in energy and speed, why aren't we all using
saddles with some sort of damped springing?
 
I know suspension seatposts exist, but even those are not popular on
road bikes.

Is some on gravel bikes and stem’s which tend to be fairly basic and move
in less than ideal ways, ie the stems tend to pivot which some riders
really don’t like.

Also while lighter they are outperformed by suspension ie Gravel suspension
forks.

But probably mostly that roadies and most Gravel riders are, are as roadies
are ie fairly conservative with technology choices.

 
ISTM that if more "suspension" is valuable via wider tires, it might
also be valuable via sprung saddles, if done right.

There is a difference between the bike being sprung and the rider,
something Specialised talked about with the Diverge and specifically the
one with suspension in the frame as well as the fork.

Which gives a different feel to for example suspension such as MTB has even
reduced down to gravel travel. Plus performance as well clearly.

 
My wife used to ride a Brooks B72. Its four curly support wires gives
just a bit of spring action. It's now on my about-town 3 speed. That
bike never goes far, but I don't detect any detriments to the slight
springiness.
 

Its not really a saddle intended for more than that, and for that use-case,
probably more that roadie and even MTBers are unlikely to like the feel of
the saddle moving in relation to the bottom bracket even if mildly.

Roger Merriman