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  #11  
Old February 23rd 18, 05:20 AM posted to rec.bicycles.tech
Jeff Liebermann
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Posts: 2,919
Default rubber compounds

On Fri, 23 Feb 2018 03:36:30 +0100, Emanuel Berg
wrote:

Jeff Liebermann wrote:

https://www.bicycling.com/bikes-gear/components/know-your-rubber-quick-start-guide-mountain-bike-tire-design
From the same paragraph as the above quote:
Hysteresis A dynamic measurement of energy
loss in the rubber compound, this can also
relate to rolling resistance or tire
"grip." A 70sA compound typically has
little energy loss, while a 40sA has
a large percentage of energy loss.


BTW what notation is 70sA and 40sA?


70 Shore A and 40 Shore A.
The "A" defines the type of penetrator used.
A is for soft rubbers, while D is for hard.
https://en.wikipedia.org/wiki/Shore_durometer#Durometer_scales

There's a bit of a muddle over the term durometer. Some say it's the
units of measure, some say it's the name of the instrument, and some
say it's both. Methinks it's the instrument name.

--
Jeff Liebermann
150 Felker St #D
http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558
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  #12  
Old February 23rd 18, 05:37 AM posted to rec.bicycles.tech
Jeff Liebermann
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Posts: 2,919
Default rubber compounds

On Fri, 23 Feb 2018 03:34:42 +0100, Emanuel Berg
wrote:

So the viscoelastic property is what makes the
tire deform/recover as it rolls
in under/away from the weight of the
bike&rider, and this is hysteresis, and the
result is loss of energy (as heat), and this is
one component of overall loss of energy which
is bunched together as rolling resistance?


No.

The visoelastic means that the material can be both viscous and
elastic at the same time. Apply some force and viscous materials flow
or ooooze. Elastic materials compress under the same force, but
return to their prior state when the force is removed.

Rubber follows a hysteresis curve such as:
https://revisionworld.com/a2-level-level-revision/physics/force-motion/solid-materials/rubber
or:
https://www.google.com/search?q=rubber+hysteresis+loop&tbm=isch
The area inside the loop represent the energy converted to heat by
rolling down the road.

The largest factor in rolling resistance is this energy loss.

There's a section in the Bicycle Science 3rd
edition book covering the details of
measuring rolling resistance


I should get that book...


The first and 3rd editions are quite different. Methinks that 3rd is
the best, but there was quite a bit of interesting stuff deleted from
the first. I have both.
https://www.alibris.com/Bicycling-Science-David-Gordon-Wilson/book/17828968

Maybe disintegrate a tire and put a piece of it
in a stand or a vice? Or/and perhaps fixate the
durometer as well, like a shop drill?


Yuck. You'll find that a bicycle tire under pressure produces a
slightly different hardness measurement than one laid flat on a table.
The thinner the tire, the larger the difference. You want the
hardness under operating conditions, which means inflated and with a
rider on the bicycle. Again, the difference is not huge, but it is
measurable.

BTW how do ISO/ETRTO measure the tire width?
I've heard it is from one bead, over the tread,
to the other bead, this distance divided by
2.5? Do they also disintegrate the tire before
doing this or do they use a string of some kind
to loop around?


I have no idea and am too lazy/busy/burned-out to look it up for you
right now.


--
Jeff Liebermann
150 Felker St #D
http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558
  #13  
Old February 23rd 18, 06:16 AM posted to rec.bicycles.tech
Frank Krygowski[_4_]
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Default rubber compounds

On 2/22/2018 11:37 PM, Jeff Liebermann wrote:
On Fri, 23 Feb 2018 03:34:42 +0100, Emanuel Berg

Rubber follows a hysteresis curve such as:
https://revisionworld.com/a2-level-level-revision/physics/force-motion/solid-materials/rubber
or:
https://www.google.com/search?q=rubber+hysteresis+loop&tbm=isch
The area inside the loop represent the energy converted to heat by
rolling down the road.

The largest factor in rolling resistance is this energy loss.


I think that's an oversimplification at best, based on an inadequate
definition of "rolling resistance."

I say this because the easiest way to reduce that rubber hysteresis
would be to completely do away with the rubber. Ride on metal tires, as
did the wagons and carriages and "boneshaker" quasi-bicycles of 150
years ago. Bingo! No hysteresis loss!

.... but tremendous rolling resistance compared to a pneumatic tire.

There's a lot more to the phenomenon than hysteresis.


--
- Frank Krygowski
  #14  
Old February 23rd 18, 01:08 PM posted to rec.bicycles.tech
Emanuel Berg[_2_]
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Posts: 1,035
Default rubber compounds

Jeff Liebermann wrote:

There's a bit of a muddle over the term
durometer. Some say it's the units of
measure, some say it's the name of the
instrument, and some say it's both.
Methinks it's the instrument name.


Sure sounds like it. But I suppose it could be
a unit as well only first time I ever heard of
it was in the context of a thing or gadget, at
least that was the way I read it.

"Use the durometer to determine the durometer!"

--
underground experts united
http://user.it.uu.se/~embe8573
  #15  
Old February 23rd 18, 01:31 PM posted to rec.bicycles.tech
Emanuel Berg[_2_]
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Posts: 1,035
Default rubber compounds

Jeff Liebermann wrote:

Rubber follows a hysteresis curve


Aha, interesting!

The energy loss is a function of stress
and strain

Stress is a force acting on a rock per unit
area. ... Stress can cause strain, if it is
sufficient to overcome the strength of the
object that is under stress. Strain is a change
in shape or size resulting from applied forces
(deformation). Rocks only strain when placed
under stress. [1]

(OK, that makes sense except what are the
"rocks" refered to?)

Also, when an elastic material (rubber) is
deformed but recovers, does that count as
strain? Probably yes as otherwise that curve
wouldn't be the one to describe it all?

That curve happens for each/any point on the
wheel for each rotation? Assuming the rider
doesn't runt the bike into a brick wall or
anything...

I have no idea and am too
lazy/busy/burned-out to look it up for you
right now.


Well, don't be stressed and absolutely not
strained by these questions

[1] https://www.youtube.com/watch?v=rRTvl7D9Ugw

--
underground experts united
http://user.it.uu.se/~embe8573
  #16  
Old February 23rd 18, 05:50 PM posted to rec.bicycles.tech
Jeff Liebermann
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Posts: 2,919
Default rubber compounds

On Fri, 23 Feb 2018 13:08:13 +0100, Emanuel Berg
wrote:

Jeff Liebermann wrote:

There's a bit of a muddle over the term
durometer. Some say it's the units of
measure, some say it's the name of the
instrument, and some say it's both.
Methinks it's the instrument name.


Sure sounds like it. But I suppose it could be
a unit as well only first time I ever heard of
it was in the context of a thing or gadget, at
least that was the way I read it.

"Use the durometer to determine the durometer!"


If you parse the word into duro meter, it is somewhat obvious that it
refers to the instrument, not the units of measure. The problem is
that the industry was not prepared for the lack of units of measure.
There are plenty of measurements that have no units, such as ratios,
proportions, indexes, modulus, mean opinion score for VoIP
intelligibility, etc.
https://en.wikipedia.org/wiki/Dimensionless_quantity
That worked fine, until it hit the automotive industry, which was not
quite accustomed to the concept. It sounded rather odd that a measure
of rubber hardness should not have some unit of measure, usually named
after the inventor or internationally, after a famous dead scientist.
Normally, it would be called XX shore units or something similar, but
not this time. Also normally, a standards committee would be assigned
to sort this out, but apparently they're too busy creating new
standards than to fix the existing ones.

However, all is not lost. This article proclaims that:
https://en.wikipedia.org/wiki/Shore_durometer
The term durometer is often used to refer to the
measurement as well as the instrument itself.
Therefore, on the authority of the Wikipedia authors and editors, you
are allowed to perpetuate the muddle.

Before you ask, zero durometer means that you punched a hole in
material under test and 100 means that the indenter needle didn't
move.
--
Jeff Liebermann
150 Felker St #D
http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558
  #17  
Old February 23rd 18, 08:02 PM posted to rec.bicycles.tech
Emanuel Berg[_2_]
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Posts: 1,035
Default rubber compounds

Jeff Liebermann wrote:

If you parse the word into duro meter, it is
somewhat obvious that it refers to the
instrument, not the units of measure.


To me the intuition is the other way around:
durometer = instrument, as in thermometer,
hygrometer ...

Before you ask, zero durometer means that you
punched a hole in material under test and 100
means that the indenter needle didn't move.


OK, but wouldn't that also depend on the
thickness of the material? Or is "strength thru
thickness" a fine way of doing it?

--
underground experts united
http://user.it.uu.se/~embe8573
  #18  
Old February 23rd 18, 08:36 PM posted to rec.bicycles.tech
Jeff Liebermann
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Posts: 2,919
Default rubber compounds

On Fri, 23 Feb 2018 20:02:06 +0100, Emanuel Berg
wrote:

Jeff Liebermann wrote:

If you parse the word into duro meter, it is
somewhat obvious that it refers to the
instrument, not the units of measure.


To me the intuition is the other way around:
durometer = instrument, as in thermometer,
hygrometer ...


Do you measure temperature in units of themometers?
Do you measure humidity in units of hydrometers?

Before you ask, zero durometer means that you
punched a hole in material under test and 100
means that the indenter needle didn't move.


OK, but wouldn't that also depend on the
thickness of the material? Or is "strength thru
thickness" a fine way of doing it?


Yes, it somewhat depends on thickness. If the "dent" produce goes
though the material and pops out the other side, you'll get a much
softer measurement than one that does NOT pop out the other side.
Similarly, stacking up a pile of rubber sheets until the dent is
totally inside the material, will produce something harder. I could
try it now with some inner tubes, but I'm in a rush to collect on a
free lunch. Maybe tonite.

--
Jeff Liebermann
150 Felker St #D
http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558
  #19  
Old February 23rd 18, 10:41 PM posted to rec.bicycles.tech
Emanuel Berg[_2_]
external usenet poster
 
Posts: 1,035
Default rubber compounds

Jeff Liebermann wrote:

To me the intuition is the other way around:
durometer = instrument, as in thermometer,
hygrometer ...


Do you measure temperature in units of
themometers? Do you measure humidity in units
of hydrometers?


I mean, "durometer" sounds like "thermometer",
"hydrometer", and so on (OK, it should be a "d"
in English), so to me, it sounds like
an instrument.

Also, one might wonder why they felt the need
to come up with a new unit for this at all!
Couldn't it be "how much power to penetrate" or
"how much power to reach a distance" or "how
long a distance for a certain power"... (I say
this without ever having used or even seen
a durometer so maybe it doesn't make sense.)

--
underground experts united
http://user.it.uu.se/~embe8573
  #20  
Old February 23rd 18, 10:50 PM posted to rec.bicycles.tech
Emanuel Berg[_2_]
external usenet poster
 
Posts: 1,035
Default rubber compounds

Jeff Liebermann wrote:

Yes, it somewhat depends on thickness. If the
"dent" produce goes though the material and
pops out the other side, you'll get a much
softer measurement than one that does NOT pop
out the other side. Similarly, stacking up
a pile of rubber sheets until the dent is
totally inside the material, will produce
something harder.


For a material M, if you penetrate
1 distance unit at the cost of C, then go on to
penetrate yet another distance unit
(i.e. 2 in total), will the cost then be 2C for
all of that?

Or will the material, altho compromised
(punctated and inflicted degree to some
degree), retain some hindering or
self-enforcing property to make the cost maybe
2^2C instead or something even higher?

Wood for example, with a drill it is perhaps
linear but chop a dagger into it and if it is
thick you won't get anywhere except scratching
the surface.

--
underground experts united
http://user.it.uu.se/~embe8573
 




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