baby powder in tires
neil....@bicyclebbs.org
Dale Thompson expains why baby powder is used in tire assembly:
> The _reason_ is that the powder allows the tube to slide more
> easily, thus there is less chance of a wrinkle being left in the tube
And Neil Goren would like to add:
The part of your tire where the rubber meets the road is constantly
deforming under weight and road conditions. Powder should actually
decrease rolling resistance, especially in larger diameter tires.
The powder should even help to stave off flats by preventing that fusing
effect - where your tube sticks to the inside of your tire casing from
years of neglect.
Put some talc in a baggie and keep your spare tube in there, smoosh it
around and you're pre-powdered and ready to go if you need to fix a flat
in the field. If I change the tire at home, I like to rub some powder in
the inside of the tire carcass.
If your riding includes water and heat, and you WILL be thankfull you
"took a powder!"
don't forget to wear a helmet and hold on tight!
tailwinds and rocky descents!
Neil Goren
SysOp --- @ eeeeYOW !!
/^\/\ --- /^\._
/\/ ^\/\ _~> (*) The Bicycle BBS
/^ /^\ (*) 619-720-1830
~ ~~~~~~~~~~
"Oh what a life.................on a FULL SUSPENSION BIKE!"
Jobst Brandt
> The part of your tire where the rubber meets the road is constantly
> deforming under weight and road conditions. Powder should actually
> decrease rolling resistance, especially in larger diameter tires.
The tube is unable to move even slightly when pressed against the
casing by inflation pressure. Any motion here would constitute
substantial frictional loss.
> The powder should even help to stave off flats by preventing that fusing
> effect - where your tube sticks to the inside of your tire casing from
> years of neglect.
The reason one put talc in car tires (ones that use tubes) is to
prevent the tube from vulcanizing to the tire at the high temperatures
that occur from friction heating at high speed. In a bicycle tire,
this is neither a problem nor a probability. A stuck tube generally
aids in retaining air when a thorn or small piece of glass causes a
puncture.
> Put some talc in a baggie and keep your spare tube in there, smoosh it
> around and you're pre-powdered and ready to go if you need to fix a flat
> in the field. If I change the tire at home, I like to rub some powder in
> the inside of the tire carcass.
A carcass is what you throw away when a tire is irreparable. The
casing is the structural part of the tire, in contrast to the tread.
> If your riding includes water and heat, and you WILL be thankful you
> "took a powder!"
I "WILL" will I? I don't know what I've been missing all these years
but I'm curious what thrill I'll get by putting talc in my tires.
> don't forget to wear a helmet and hold on tight!
> tailwinds and rocky descents!
Oh, now I get it. Yes, and don't forget to tell your mother where you
are going before you leave on your bicycle ride.
Jobst Brandt <jbr...@hpl.hp.com>
David J. Kroth x65799
Jobst Brandt wrote:
> The reason one put talc in car tires (ones that use tubes) is to
> prevent the tube from vulcanizing to the tire at the high temperatures
> that occur from friction heating at high speed. In a bicycle tire,
> this is neither a problem nor a probability.
Hey Jobst, speak for yourself. On my road bike, I regularly maintain
speeds typical of automobiles for great distances (100's of miles).
My tubes and tires need plenty of talc to prevent exactly the vulcanizing
process you describe.
Dave
kr...@kodak.com
PS. BIG :-) for the humor disadvantaged.
Jobst Brandt
> Jobst Brandt wrote:
>
>> The reason one put talc in car tires (ones that use tubes) is to
>> prevent the tube from vulcanizing to the tire at the high temperatures
>> that occur from friction heating at high speed. In a bicycle tire,
>> this is neither a problem nor a probability.
> ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
>
> Hey Jobst, speak for yourself. On my road bike, I regularly maintain
> speeds typical of automobiles for great distances (100's of miles).
> My tubes and tires need plenty of talc to prevent exactly the vulcanizing
> process you describe.
It is my experience (and I speak for myself) that cars on highways
travel about 70 mph and that the substantially larger cross section
tires become hot enough to be uncomfortable to the touch in warm
weather. I don't believe for a moment that you ride that fast, have
car tires on your bicycle, that the tires get as hot as the surface of
the road, or that the tubes cannot be removed without incident after
several thousand miles of use. My tires certainly have no such
problem as don't the thousands of bicycle tires that are in use on the
road without talc.
I'm sure you also knock on wood, throw sand over your shoulder and
avoid black cats in your path. It works, I swear. Talc in your tire
casing works equally well. But just by the way, it was claimed it
prevents flats. That is also untrue.
Jobst Brandt <jbr...@hpl.hp.com>
kh...@parcplace.com
>David Kroth writes:
I'm not claiming that talc prevents vulcanizing or reduces flats, but I
can attest that w/o talc, I did have an incidence of my MTB inner tubes
getting sufficiently stuck to the inside of the tire casing that I had
to deliberately "peel" them out when I was swapping tires. (I have not
experienced this adhesion with talc-ed tubes.)
It's plausible that under such conditions a marginally affixed patch
would have remained stuck to the casing instead -- whereas with the tube
having been talc-ed neither tube nor patch would've adhered to the casing.
--
Michael Khaw kh...@parcplace.com (or khaw%parcpl...@netcom.com)
ParcPlace Systems, Sunnyvale, CA PRODUCT INFO: in...@parcplace.com
David J. Kroth x65799
>
>> David Kroth writes:
> ... Humorous 'tall tale' about riding fast and long...
>
> ... Jobst crushes him with a response...and continues...
>
> I'm sure you also knock on wood, throw sand over your shoulder and
> avoid black cats in your path. It works, I swear. Talc in your tire
> casing works equally well. But just by the way, it was claimed it
> prevents flats. That is also untrue.
No! No! No! The talc in the tires stops the black cats from
crossing your path in the first place. The black cats are responsible
for 90% of all bicycle flats!
Dave
kr...@kodak.com
PS. More :-) all around.
Shane McRoberts
: David Kroth writes:
: > Jobst Brandt wrote:
: >
: >> The reason one put talc in car tires (ones that use tubes) is to
: >> prevent the tube from vulcanizing to the tire at the high temperatures
: >> that occur from friction heating at high speed. In a bicycle tire,
: >> this is neither a problem nor a probability.
: > ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
: >
: > Hey Jobst, speak for yourself. On my road bike, I regularly maintain
: > speeds typical of automobiles for great distances (100's of miles).
: > My tubes and tires need plenty of talc to prevent exactly the vulcanizing
: > process you describe.
: It is my experience (and I speak for myself) that cars on highways
: travel about 70 mph and that the substantially larger cross section
: [blah, blah]
: Jobst Brandt <jbr...@hpl.hp.com>
Jobst, you cut off the part of the message where he explained (quote:
"for the humor disadvantaged") that he was JOKING.
Shane
=====================
| j.shane.mcroberts |
|mitek systems, inc.|
| |
| j...@miteksys.com |
=====================
Paul Sumner
> It is my experience (and I speak for myself) that cars on highways
> travel about 70 mph and that the substantially larger cross section
> tires become hot enough to be uncomfortable to the touch in warm
> weather. I don't believe for a moment that you ride that fast, have
> car tires on your bicycle, that the tires get as hot as the surface of
> the road, or that the tubes cannot be removed without incident after
> several thousand miles of use. My tires certainly have no such
> problem as don't the thousands of bicycle tires that are in use on the
> road without talc.
I don't ride at high speed for long periods, but I do experience tire
stick. For example: when riding downhill, because of braking, the
temperature will rise substantially. Next time you ride a long downhill
grab your tire, you'll feel it.
Paul Sumner ( Team JOLT / SoftRide )
Jobst Brandt
> I'm not claiming that talc prevents vulcanizing or reduces flats, but I
> can attest that w/o talc, I did have an incidence of my MTB inner tubes
> getting sufficiently stuck to the inside of the tire casing that I had
> to deliberately "peel" them out when I was swapping tires. (I have not
> experienced this adhesion with talc-ed tubes.)
> It's plausible that under such conditions a marginally affixed patch
> would have remained stuck to the casing instead -- whereas with the tube
> having been talc-ed neither tube nor patch would've adhered to the casing.
Well, until you peel a patch from your tube you should be glad that
the tubes are stuck in there because a pinch or puncture will not lose
air as fast if the air were free to escape into the casing. Most of
the air must escape through the hole in the casing (that doesn't
stretch like the tube), if any. I take it as an advantage, and if
your patches stick to the casing better than the tube to wich you
attach them, you should improve your patching technique. This is
probably a good patch quality check.
Jobst Brandt <jbr...@hpl.hp.com>
Jobst Brandt
> I don't ride at high speed for long periods, but I do experience tire
> stick. For example: when riding downhill, because of braking, the
> temperature will rise substantially. Next time you ride a long downhill
> grab your tire, you'll feel it.
I think you are imagining this. Even the back of the brake pads don't
warm up perceptibly because they, as the tires, are made of material
that insulates exceptionally well. The tire may get its air heated but
even this is more than countered by the moving air on the outside that
has many times the convective ability of the trapped air inside.
As I said in another reply, that the tube sticks in the casing is more
an advantage than a disadvantage. And again, the original contention
is that talc prevents flats. It does not.
Jobst Brandt <jbr...@hpl.hp.com>
Geoff Oakley
I'm not claiming that talc prevents vulcanizing or reduces flats, but I
can attest that w/o talc, I did have an incidence of my MTB inner tubes
getting sufficiently stuck to the inside of the tire casing that I had
to deliberately "peel" them out when I was swapping tires. (I have not
experienced this adhesion with talc-ed tubes.)
It's plausible that under such conditions a marginally affixed patch
would have remained stuck to the casing instead -- whereas with the tube
having been talc-ed neither tube nor patch would've adhered to the casing.
I previously used talc for exactly this reason, but have stopped.
For small cuts in the tyre (say, less that 4mm) I can apply a normal
tube patch to the inside of the tyre and pump back up to 130psi.
Without the patch, it only take a couple of cords cut in the tyre
casing before the tube developes a hernia (at 130psi), and leads to
very spectacular blowouts.
Talc on the inside of the tyre is very good at preventing the patch
from adhering.
I ride along enough glass-strewn streets that my tyres (not the tubes)
usually have half a dozen patches before the tread rubber wears out.
geoff o
--
Geoff Oakley -- System Administrator
Mail: Geoff Oakley, CS&E, UNSW, Sydney, NSW 2052, Australia
Email: geo...@cse.unsw.edu.au
Phone: +61 2 385 4043
Fax: +61 2 313 7987
Tim Bradshaw
> I'm not claiming that talc prevents vulcanizing or reduces flats, but I
> can attest that w/o talc, I did have an incidence of my MTB inner tubes
> getting sufficiently stuck to the inside of the tire casing that I had
> to deliberately "peel" them out when I was swapping tires. (I have not
> experienced this adhesion with talc-ed tubes.)
I've had tubes stick to tyres. I'm sure it wasn't because I ride at
millions of MPH down cliffs, but because the tyres were somehow sticky
on the inside (they were cheap ones that came with the bike). I still
have one of them which I'd like to use again until it wears out, but
it's a real pain -- the tube sticks pretty thoroughly to it, making it
hard to get out (I mean, you really have to *pull* it). Will talc
cure this? I've tried washing it, to no effect.
Thanks,
--tim
Dave Hayes
geo...@cse.unsw.edu.au (Geoff Oakley) wrote:
> For small cuts in the tyre (say, less that 4mm) I can apply a normal
> tube patch to the inside of the tyre and pump back up to 130psi.
> Without the patch, it only take a couple of cords cut in the tyre
> casing before the tube developes a hernia (at 130psi), and leads to
> very spectacular blowouts.
Use fabric--such as canvas or (better) casing salvaged from a spent sew-up
tire--for "booting" a cut in a tire casing. At 130 psi, rubber patches can
protrude through relatively small cuts. Fabric will not.
> Talc on the inside of the tyre is very good at preventing the patch
> from adhering.
Always clean the surface of any object before applying adhesive. I've found
that lacquer thinner or acetone work well for cleaning the inside of tires.
> I ride along enough glass-strewn streets that my tyres (not the tubes)
> usually have half a dozen patches before the tread rubber wears out.
Sounds as though NSW should institute a deposit on glass bottles...
Dave Hayes
Paul Sumner
> I think you are imagining this. Even the back of the brake pads don't
> warm up perceptibly because they, as the tires, are made of material
> that insulates exceptionally well. The tire may get its air heated but
> even this is more than countered by the moving air on the outside that
> has many times the convective ability of the trapped air inside.
>
> As I said in another reply, that the tube sticks in the casing is more
> an advantage than a disadvantage. And again, the original contention
> is that talc prevents flats. It does not.
>
> Jobst Brandt <jbr...@hpl.hp.com>
Excuse me, but your simply wrong. I'm not imagining anything. The tire
and rim get very hot, while the tube may not actually vulcanize to the
tire, it does adhere to the tire. This is well known fact.
As far as the heat, there is Tour story that goes like this: I don't
remember the stage, but it started out with a 5-10km downhill which was
controled (where no one can pass a lead car going like 20mph) at the
bottom there were something like 30 flats- it seems everybody's rims had
gotten so hot that the glue (sew-up) had loosened up, and Voila, valve
stems were popping off like crazy.
Your reaching when you say that a stuck tube may loose air more slowly, come on.
It may or may not prevent flats. It does make tube repair a bit easier,
and does prevent to freshly glued patch from sticking to the tube.
Darryn Schneider
haven't seen all of the mail on this debate
but the few I've seen are very interesting from
a scientific point. I think there has been enough
argument to be sure that the wheel does heat up and
there is an easy explanation for it that might
have already been pointed out.
the heating is caused by the adiabatic processes in
the compression of the air. Go over a bump - air compressed
- heat released - pressure equalizes but heat not reabsorbed
in process - therefore air, thus tyre heats up.
Example - quite a few years ago an Australian 'inventor'
came up with the idea of wings on jet wheels to make them
spin before landing. Thus, less wear from skidding on landing.
When aircraft manufaturers did not take up the idea it
was called a scam between tyre man. and aircraft companies.
However, the rubber left behind contains a large amount of
heat. this heat comes from processes such as what probably
happens on the bike tyres. If the heat was not removed through
the rubber left behind, the air would expand and the tyre would
explode. This is one of the reason Jumbo's have so many tyres.
True !
Just thought I'd throw this in.
Probably won't help, but its fun.
Darryn
Jobst Brandt
> Excuse me, but your simply wrong. I'm not imagining anything. The
> tire and rim get very hot, while the tube may not actually vulcanize
> to the tire, it does adhere to the tire. This is well known fact.
That tubes stick to tires is true. That this is a disadvantage or
that it causes flats is not true. The tread of the tire may get
perceptibly warm from braking and you can feel that it is not as cold
as it was but it does not get hot. The term hot is a generous
exaggeration.
> As far as the heat, there is Tour story that goes like this: I don't
> remember the stage, but it started out with a 5-10km downhill which was
> controled (where no one can pass a lead car going like 20mph) at the
> bottom there were something like 30 flats- it seems everybody's rims had
> gotten so hot that the glue (sew-up) had loosened up, and Voila, valve
> stems were popping off like crazy.
I have presented other more quantitative evidence of brake heating
here, and that was that a tubular rim that had taken on water in
snowfields and stream crossings generated steam that hissed as it
escaped arounbd the stem nut while braking for each hairpin on a
mountain road. That should be sufficient evidence that tubular glue
melts easily from braking. This was one of my greatest concerns in
the days when I had to use tubulars on my tours in the mountains.
This does not mean in the least that talcum is needed nor that tubes
get hot enough to vulcanize to the tire as they do in truck and car
tires. For these it is common to tear a tube on removal if no release
powder of some kind was used.
> Your reaching when you say that a stuck tube may loose air more
> slowly, come on.
Well look at it this way. If you get a thorn puncture or one from a
Michelin wire, the hole in the casing is plugged while the tube that
is stretched from inflation opens a hole to let the air out. In the
stuck tube condition, the air does not exit as fast as it would
otherwise. I have often been able to ride the three miles home from
work by inflating my tire that had a thorn from riding to work, that
is, if the tube has been in there awhile and is well stuck. Otherwise
the tire leaks pretty fast.
> It may or may not prevent flats. It does make tube repair a bit
> easier, and does prevent to freshly glued patch from sticking to the
> tube.
It has been mentioned now and then, and I think in this thread, that
talc is a good thing to put on the exposed glue around a patch and I
agree. You keep protesting and in light of the contention that it
prevents flats, I keep wondering why you persist if you don't think
that it does. It seems we are in agreement on that, but I'm not sure.
Jobst Brandt <jbr...@hpl.hp.com>
Jobst Brandt
> the heating is caused by the adiabatic processes in the compression
> of the air. Go over a bump - air compressed - heat released -
> pressure equalizes but heat not reabsorbed in process - therefore
> air, thus tyre heats up.
Oh get off it. There isn't enough work there to feel heat. Just look
at the absolute volume change. Besides, it's transient so the average
increase is zero. It's insignificant.
> Example - quite a few years ago an Australian 'inventor'
> came up with the idea of wings on jet wheels to make them
> spin before landing. Thus, less wear from skidding on landing.
> When aircraft manufacturers did not take up the idea it
> was called a scam between tyre man. and aircraft companies.
Sure, the world is full of commercial conspiracies on the highest
level. Fortunately there are competing interests of relatively equal
magnitude to prevent this, including the military and space agency.
The airframe industry, tire manufacturers, and users of the aircraft
have substantial interests in this matter and would not acquiesce in
some payoff scheme. Besides, the rotating wheel vanes were proposed a
long long time ago. How old are you anyway.
> However, the rubber left behind contains a large amount of heat.
> this heat comes from processes such as what probably happens on the
> bike tyres. If the heat was not removed through the rubber left
> behind, the air would expand and the tyre would explode. This is one
> of the reason Jumbo's have so many tyres.
The process is known as skidding or rubbing friction. It is not akin to
the heating you suggest as coming from compression work.
> Just thought I'd throw this in. Probably won't help, but its fun.
It's not only that but it isn't related to reality. Thanks alot.
Jobst Brandt <jbr...@hpl.hp.com>
Kevin Jarrett
DS> Just thought I'd throw this in. Probably won't help, but its fun.
Here's another angle: AirB recommends you talc the inside of tires
when installing their tubes. In fact, they come shipped in a plastic
bag with talc inside. Perhaps this helps preserve the latex?
-kj-
+--------------------------------------------------------------------+
| Kevin M. Jarrett Quaker Chemical Corporation Conshohocken PA USA |
| BBS: 609/232-1245 Internet: kevin....@compudata.com |
+--------------------------------------------------------------------+
* RM 1.3 01757 * A friend in need is a PEST indeed...
-----------------------------------------------------------------------------
Internet: kevin....@compudata.com (Kevin Jarrett)
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Darryn Schneider
I do not believe that any heating process has any effect
on bike tyres. I do believe that frictional heat transfered to
the tyres is small and that the heat released due to compression
of the air in the tube when going over a rough surface (ie any road)
would be as large and may dominate. The volume might not be large
but then the volume of air in a tube is not large and yet
just feel your valve to see that a largish amount of heat
is released when it is inflated.
I have lost my notes on this effect in taxiing aircraft tyres
and I am not going to put any effort into such a trivial
point. Especially against arguments like :
>Besides, it's transient so the average
>increase is zero. It's insignificant.
If you don't understand that this statement is wrong
then there is no point continuing and I'll just suggest
you go read an undergraduate text.
Now I'm going to do something much more enjoyable,
go for a ride.
John Frampton
: >Besides, it's transient so the average
: >increase is zero. It's insignificant.
: If you don't understand that this statement is wrong
: then there is no point continuing and I'll just suggest
: you go read an undergraduate text.
: Now I'm going to do something much more enjoyable,
: go for a ride.
I've read an undergraduate text (a while ago) and the point you are
trying to make is not clear at all. Isn't it true that after the
temperature of the air in a tire is raised by the compression of going
over a bump, it is then cooled by expansion back to the orginal volume?
Or are you saying that hysteresis losses heat up the tire? Seems
doubtful that it is significant. Perhaps I misunderstand you and you
intended to discuss insignificant effects.
John Frampton
Jobst Brandt
> Here's another angle: AirB recommends you talc the inside of tires
> when installing their tubes. In fact, they come shipped in a plastic
> bag with talc inside. Perhaps this helps preserve the latex?
I think they are more concerned with wrinkles that are easily included
when installing thin latex tubes if the tube does not move freely in
the casing before and during inflation. Talc is good for that.
Jobst Brandt <jbr...@hpl.hp.com>
Jobst Brandt
> I do not believe that any heating process has any effect on bike
> tyres. I do believe that frictional heat transfered to the tyres is
> small and that the heat released due to compression of the air in
> the tube when going over a rough surface (ie any road) would be as
> large and may dominate. The volume might not be large but then the
> volume of air in a tube is not large and yet just feel your valve to
> see that a largish amount of heat is released when it is inflated.
The heat of compressing the air to fill a tire is the result of an
eightfold reduction in volume and it is retained, not just present
during a short duration rebound of a few milliseconds. In spite of
that, the temperature change is not perceptible to the touch on the
tread after inflation.
> I have lost my notes on this effect in taxiing aircraft tyres
> and I am not going to put any effort into such a trivial
> point. Especially against arguments like :
What notes? As I said, I heard of this "invention" many years ago
and it was old then.
>> Besides, it's transient so the average increase is zero. It's
>> insignificant.
Oh, what don't you like about this. The slight reduction in volume
from a road irregularity increases the air temperature ever so
slightly before the air again expands and reduces temperature. During
that period of a few milliseconds, the heat transfer in the rubber tube
that is a good insulator might change a few hundredths of a degree.
> If you don't understand that this statement is wrong then there is
> no point continuing and I'll just suggest you go read an
> undergraduate text.
How about as grade school or even a kindergarten text. I know you
read all that before you finished graduate school, I assume from
your choice of words. I don't, however, see any evidence in what
you write that you understand these things or I would expect some
explanation about how you perceive these thermodynamic effects to
occur.
> Now I'm going to do something much more enjoyable, go for a ride.
Tu tu, I gotta run now too. Don't overheat your tires.
Jobst Brandt <jbr...@hpl.hp.com>
Paul Sumner
> That tubes stick to tires is true. That this is a disadvantage or
> that it causes flats is not true. The tread of the tire may get
> perceptibly warm from braking and you can feel that it is not as cold
> as it was but it does not get hot. The term hot is a generous
> exaggeration.
What I mean by Hot, is hot enough where you don't want to grab the rim and
hold onto it.
> It has been mentioned now and then, and I think in this thread, that
> talc is a good thing to put on the exposed glue around a patch and I
> agree. You keep protesting and in light of the contention that it
> prevents flats, I keep wondering why you persist if you don't think
> that it does. It seems we are in agreement on that, but I'm not sure.
I don't usually bother to talc my tires and I don't think its a bad thing
either. The only real disagreement that I had was over the heat issue, so
I probabily shoudn't have argued. We are in agreement that talc provides
little or no extra resistance to flats.
Ray Bowman
In Message-ID: <D14yJ...@hpl.hp.com>
Date: Wed, 21 Dec 1994 00:54:57 GMT
Jobst Brandt (jbr...@hpl.hp.com) writes:
>Kevin Jarrett writes:
Jobst is certainly correct about talc being important in preventing tube
damage when the tube is installed. In addition to being effective in
preventing wrinkles, it is effective in minimizing thin, highly-stressed
areas in the installed tube. Talc probably helps to avoid other problems
also, such as the tube getting pinched between the valve re-inforcement
molding and the rim, the tire beads and the rim, or tire levers and the
rim.
Talc will also have SOME effect on rolling resistance, but it is not yet
known whether this is beneficial or harmful. As the tire rolls, the tire
rubber (and other tire materials) bend and stretch at the contact patch.
Due to energy losses in this process (hysteresis losses), the tire has
resistance to rolling, even if there is no scrubbing at the tire-road
interface. If the tube is fully adhered to the tire, it will bend and
stretch with the tire and add to the rolling resistance by way of its
hysteresis losses, but there will be no energy loss from scrubbing at the
tire-tube interface. If the tire-tube interface is slick enough, from
talc or any other lubricant, to allow tube scrubbing, then there will also
be friction losses. However, this movement of the tube lessens the
stretching of the tube and thus lessens the losses from hysteresis in the
tube rubber. The net effect is difficult to measure or to predict and, no
doubt, depends on tire pressure. IMO, talc is likely to increase rolling
resistance by a small but significant amount, but I wouldn’t bet much on
this guess.
Ray Bowman
Jobst Brandt
[...]
> Further, I agree that stuck tubes may not entirely be a disadvantage
> (see my other post today in this thread). However, stuck tubes DO
> increase the frequency of flats.
> The December issue of Cycling Science has an article by myself and
> co-workers that gives quantitative measurements of how far points
> must penetrate (beyond the tire wall) to puncture typical tubes
> (butyl, latex, and thorn-proof) and typical tire liners. These
> tests were done with talced tubes, so the tubes were free to indent
> by various depths and therefore resist pentration by the points.
> Depending mainly on point sharpness, even butyl tubes can indent
> considerably before being pierced, if they are not strongly adhered.
> For tubes thoroughly stuck to tires, the puncture resistance will
> unquestionably be much less. Moderate adhesion can be expected to
> have only a moderate effect on flat frequency; but, for many people,
> any increase in flat frequency is a significant problem.
I can add that to the evidence I have that "Cycling Science" is
technically "out to lunch". If a tube at 120 psi makes a "tent" over
a penetrating object and is affected by the adhesion of the tube to
the tire, then they have a conceptual problem. Static tests don't do
much for evaluating puncture resistance as was demonstrated by Clement
when they presented their puncture proof tubes that were demonstrated
on a bed of nails that penetrated the casing. It was miraculous to
observe how they held air in the store. These tires also went flat
from the same little pieces from brown beer bottles as all other
tires, with latex or butyl tubes.
Ivory (cycling(science)) towers abound!
Jobst Brandt <jbr...@hpl.hp.com>
Jobst Brandt
> [...] Talc probably helps to avoid other problems also, such as the
> tube getting pinched between the valve reinforcement molding and
> the rim, the tire beads and the rim, or tire levers and the rim.
I think that is attributing greater powers to talc than it has.
Besides, these are skill problems that can not be dusted away with a
dash of talc. Mounting a tire still requires a bit of manual facility
that is not contained in talc.
> Talc will also have SOME effect on rolling resistance, but it is not
> yet known whether this is beneficial or harmful. As the tire rolls,
> the tire rubber (and other tire materials) bend and stretch at the
> contact patch. Due to energy losses in this process (hysteresis
> losses), the tire has resistance to rolling, even if there is no
> scrubbing at the tire-road interface. If the tube is fully adhered
> to the tire, it will bend and stretch with the tire and add to the
> rolling resistance by way of its hysteresis losses, but there will
> be no energy loss from scrubbing at the tire-tube interface.
An inflated tube does not move in the casing because it is
unambiguously pressed against the casing that does not stretch
sufficiently to cause any significant lateral force in the tube.
Talc, after all, is a fine grained solid that does not lubricate.
There is a slight nibbling effect at the bead to rim interface but
this is not affected by talc. There is no scrubbing between the tube
and casing! Rolling resistance is almost entirely a result of losses
in flexing the tube, tread, and tire casing in the tire and by
scrubbing at the point where the tread lifts off the road.
Jobst Brandt <jbr...@hpl.hp.com>
Ray Bowman
In Message-ID: <D131M...@hpl.hp.com>
Date: Tue, 20 Dec 1994 00:06:16 GMT
Jobst Brandt ( jbr...@hpl.hp.com) writes:
>Paul Sumner writes:
>> Excuse me, but your simply wrong. I'm not imagining anything. The
>> tire and rim get very hot, while the tube may not actually vulcanize
>> to the tire, it does adhere to the tire. This is well known fact.
>That tubes stick to tires is true. That this is a disadvantage or
>that it causes flats is not true. The tread of the tire may get
>perceptibly warm from braking and you can feel that it is not as cold
>as it was but it does not get hot. The term hot is a generous
>exaggeration.
Major snip on heat issues.
>> Your reaching when you say that a stuck tube may loose air more
>> slowly, come on.
>Well look at it this way. If you get a thorn puncture or one from a
>Michelin wire, the hole in the casing is plugged while the tube that
>is stretched from inflation opens a hole to let the air out. In the
>stuck tube condition, the air does not exit as fast as it would
>otherwise.
Snip.
Jobst, your analysis about (thoroughly) stuck tubes losing air more slowly
from punctures is certainly correct; and clearly stated. Further, I agree
that stuck tubes may not entirely be a disadvantage (see my other post
today in this thread). However, stuck tubes DO increase the frequency of
flats.
The December issue of Cycling Science has an article by myself and
co-workers that gives quantitative measurements of how far points must
penetrate (beyond the tire wall) to puncture typical tubes (butyl, latex,
and thorn-proof) and typical tire liners. These tests were done with
talced tubes, so the tubes were free to indent by various depths and
therefore resist pentration by the points. Depending mainly on point
sharpness, even butyl tubes can indent considerably before being pierced,
if they are not strongly adhered. For tubes thoroughly stuck to tires,
the puncture resistance will unquestionably be much less. Moderate
adhesion can be expected to have only a moderate effect on flat frequency;
but, for many people, any increase in flat frequency is a significant
problem.
Ray Bowman
Ray Bowman
Date: Tue, 3 Jan 1995 16:57:36 GMT
Jobst Brandt writes:
>Ray Bowman writes:
If the tube is not strongly stuck to the tire, a penetrating nail, for
example, does in fact cause the tube (and the tire liner, if present) to
form a sizable “tent”. The tent grows in height as the nail penetration
continues and the force on the nail point increases. The tube is
punctured only when the nail penetrates far enough inside the tire. It is
surprising that this tent height can be considerable, but both the
“static” tests reported in the December issue of Cycling Science and some
earlier “dynamic” (that is, “ride-over”) tests are in close agreement and
prove unequivocally that tubes have considerable resistance to being
punctured by nails, even in high pressure tires. Further, myself and
co-workers have also successfully made video recordings of the tents that
form before tubes rupture (by using a special pressure chamber, with
windows, that mimics a tire section). The tent heights at tube rupture in
this chamber were approximately the same as those we measured for tubes in
actual tires, providing a third proof that tents of typically 2 to 20 mm
in height form before rupture occurs (depending on the point sharpness and
the tube material).
If you have any actual evidence of general technical incompetence on the
part of Cycling Science authors, I suggest that you post a temperate,
factual, and well-thought-out critique under an appropiate subject title
so we can all understand why you keep taking pot shots at this much-needed
(IMO) journal. Otherwise, you appear to be only ranting -- and this hurts
your credibility.
Ray Bowman
Ray Bowman
Date: Tue, 3 Jan 1995 17:20:20 GMT
Jobst Brandt writes:
>Ray Bowman writes:
>> [...] Talc probably helps to avoid other problems also, such as the
>> tube getting pinched between the valve reinforcement molding and
>> the rim, the tire beads and the rim, or tire levers and the rim.
>I think that is attributing greater powers to talc than it has.
>Besides, these are skill problems that can not be dusted away with a
>dash of talc. Mounting a tire still requires a bit of manual facility
>that is not contained in talc.
I said that talc HELPS to prevent tube mounting problems, not that it is a
substitute for good technique in installing tubes. Do you question that a
slippery tube is less likely to snag or pinch than a sticky one?
>> Talc will also have SOME effect on rolling resistance, but it is not
>> yet known whether this is beneficial or harmful. As the tire rolls,
>> the tire rubber (and other tire materials) bend and stretch at the
>> contact patch. Due to energy losses in this process (hysteresis
>> losses), the tire has resistance to rolling, even if there is no
>> scrubbing at the tire-road interface. If the tube is fully adhered
>> to the tire, it will bend and stretch with the tire and add to the
>> rolling resistance by way of its hysteresis losses, but there will
>> be no energy loss from scrubbing at the tire-tube interface.
>An inflated tube does not move in the casing because it is
>unambiguously pressed against the casing that does not stretch
>sufficiently to cause any significant lateral force in the tube.
>Talc, after all, is a fine grained solid that does not lubricate.
>There is a slight nibbling effect at the bead to rim interface but
>this is not affected by talc. There is no scrubbing between the tube
>and casing! Rolling resistance is almost entirely a result of losses
>in flexing the tube, tread, and tire casing in the tire and by
>scrubbing at the point where the tread lifts off the road.
While tire casings are fairly stiff, they do stretch significantly (much
more easily in some directions than in others). And powdered talc happens
to be a good lubricant for rubber, a fact widely known both inside and
ouside the rubber industry. So, it may not require much lateral force to
cause a talced tube to slip. This is why I said:
>If the tire-tube interface is slick enough, from talc or any other
lubricant, to allow tube >scrubbing, then there will also be friction
losses. However, this movement of the tube >lessens the stretching of the
tube and thus lessens the losses from hysteresis in the tube >rubber. The
net effect is difficult to measure or to predict and, no doubt, depends on
>tire pressure. IMO, talc is likely to increase rolling resistance by a
small but significant >amount, but I wouldn’t bet much on this guess.
Please note that I postulated enough lubrication to allow slip and that I
clearly indicated I was discussing an effect that would be small. My main
reason for making an analysis of the effects of talc was to discuss the
basic mechanics involved because there has been some confusion about this.
I have several times seen or heard such statements as “talc is needed to
reduce the friction loss due to scrubbing between the tube and casing”.
For a long time I have questioned this concept because using no talc, or a
modest amount, would prevent or minimize any slipping, perhaps resulting
in less energy loss than making the tube slippery.
Ray Bowman
Mike DeMicco
I have noticed that, even with talc, my latex tubes still stick to the
inside of my mountain bike tires after they've been mounted for a
while. From what I understand, silicone won't degrade rubber.
_________________________________________________________
Opinions expressed here are my own and not my employer's.
Mike De Micco <demi...@llnl.gov>
Jobst Brandt
> “static” tests reported in the December issue of Cycling
> Science and some earlier “dynamic” (that is,
> “ride-over”) tests are in close agreement and prove
> unequivocally that tubes have considerable resistance to being
> punctured by nails, even in high pressure tires. Further, myself
> and co-workers have also successfully made video recordings of the
> tents that form before tubes rupture (by using a special pressure
> chamber, with windows, that mimics a tire section). The tent
> heights at tube rupture in this chamber were approximately the same
> as those we measured for tubes in actual tires, providing a third
> proof that tents of typically 2 to 20 mm in height form before
> rupture occurs (depending on the point sharpness and the tube
> material).
> If you have any actual evidence of general technical incompetence on
> the part of Cycling Science authors, I suggest that you post a
> temperate, factual, and well-thought-out critique under an
> appropriate subject title so we can all understand why you keep
> taking pot shots at this much-needed (IMO) journal. Otherwise, you
> appear to be only ranting -- and this hurts your credibility.
"temperate"? The luke warm unreal articles such as the Power Post
promotional article, certainly damage credibility.
I think you are still thinking in the terms of the tests performed.
Over how many wheel rotations do you think these tents survive? Just
the exposure of the stitching against the tube in a tubular tire causes
flats. Mispositioned seam protectors inside tubulars were noted for
causing flats. A boot, not properly feathered, will nibble through a
standard black butyl tube in sufficient mileage.
These tests are, as I stated, as meaningless as the claims of latex
tube demonstrations in which nails penetrated the tire to a depth of
a half inch and released no air. Meanwhile these same tubes got
nibble holes at the tire casing edge.
Jobst Brandt <jbr...@hpl.hp.com>
Jobst Brandt
> I said that talc HELPS to prevent tube mounting problems, not that
> it is a substitute for good technique in installing tubes. Do you
> question that a slippery tube is less likely to snag or pinch than a
> sticky one?
Talc is not a lubricant. It is a release agent that prevents
adhesion. An entirely clean tube will adhere to other smooth surfaces
by its compliant and smooth surface, however, a tube already has mold
release on its surface from manufacture. It is for this reason that
the surface must be abraded to improve patch retention.
> While tire casings are fairly stiff, they do stretch significantly
> (much more easily in some directions than in others). And powdered
> talc happens to be a good lubricant for rubber, a fact widely known
> both inside and outside the rubber industry. So, it may not require
> much lateral force to cause a talced tube to slip.
Because talc is not a lubricant, this will require substantial lateral
force to move. Considering the rigidity of the casing in comparison
to the tube, it should be apparent that for the minuscule distortion
of the tire, the tube adapts easily as it works in-place. If you have
looked at a tube that has been in the same tire without interruption
(by removal for repair) you will have noticed that the casing cords
and other features of the tire have fretted their images into the
surface of the tube. This indicates that the tube remained indexed
to the tire and that it was fretting. Talc has no effect on this
phenomenon.
Jobst Brandt <jbr...@hpl.hp.com>
Thomas H. Kunich
Ray Bowman <rayb...@aol.com> wrote:
>And powdered talc happens
>to be a good lubricant for rubber, a fact widely known both inside and
>ouside the rubber industry.
Well, in my stupidity I would have thought that talc isn't a 'lubricant'
of any kind at all. I would simply have assumed that talc in inserted
to prevent rubber from contacting rubber and therefore prevent the welding
that occurs and also the high friction coefficient of rubber on rubber.
Ray Bowman
Date: Fri, 6 Jan 1995 18:01:29 GMT
Jobst Brandt writes:
>Ray Bowman writes:
>> “static” tests reported in the December issue of Cycling
>> Science and some earlier “dynamic” (that is,
>> “ride-over”) tests are in close agreement and prove
>> unequivocally that tubes have considerable resistance to being
>> punctured by nails, even in high pressure tires. Further, myself
>> and co-workers have also successfully made video recordings of the
>> tents that form before tubes rupture (by using a special pressure
>> chamber, with windows, that mimics a tire section). The tent
>> heights at tube rupture in this chamber were approximately the same
>> as those we measured for tubes in actual tires, providing a third
>> proof that tents of typically 2 to 20 mm in height form before
>> rupture occurs (depending on the point sharpness and the tube
>> material).
>I think you are still thinking in the terms of the tests performed.
>Over how many wheel rotations do you think these tents survive? Just
>the exposure of the stitching against the tube in a tubular tire causes
>flats. Mispositioned seam protectors inside tubulars were noted for
>causing flats. A boot, not properly feathered, will nibble through a
>standard black butyl tube in sufficient mileage.
>These tests are, as I stated, as meaningless as the claims of latex
>tube demonstrations in which nails penetrated the tire to a depth of
>a half inch and released no air. Meanwhile these same tubes got
>nibble holes at the tire casing edge.
We are certainly in agreement that penetrating objects left in tires will
soon fret through the tube if it is not initially punctured. However,
penetrators do not always become embedded in the tire, and people
frequently remove embedded objects immediately. So, on these grounds
alone, the tests in question are not meaningless. Moreover, I think you
are not properly addressing the actual purposes and conclusions of the
tests.
The main purpose of the recent tests, the ones reported in the December 94
issue of Cycling Science, was to quantitatively evaluate products that
claim to be effective in preventing punctures. We found that they are not
very effective, even in preventing immediate punctures. However, the
products were shown to be somewhat effective and, for the first time,
their relative performance was measured objectively. The results are FAR
more reliable and valuable than the usual chat about personal experiences
with such products. The main limitation of both series of tests is that
they only involved pointed objects, not that they did not investigate the
effects of prolonged riding with embedded objects in tires. We had to
ignore both of these considerations due to experimental difficulties and
limited resources.
Your comments about later failures due to fretting strengthen my belief
that no existing puncture-preventing product is very effective. I don’t
see how any “armoring” product” can be truly effective in preventing
punctures without adding so much stiffness and rolling resistance as to be
very undesirable. I have believed this for a long time, which is why my
own efforts have been to develop effective tube sealants. These can be,
and a few actually are, highly effective for the great majority of tube
failures.
Jobst also writes:
>Ray writes:
>> If you have any actual evidence of general technical incompetence on
>> the part of Cycling Science authors, I suggest that you post a
>> temperate, factual, and well-thought-out critique under an
>> appropriate subject title so we can all understand why you keep
>> taking pot shots at this much-needed (IMO) journal. Otherwise, you
>> appear to be only ranting -- and this hurts your credibility.
>"temperate"? The luke warm unreal articles such as the Power Post
>promotional article, certainly damage credibility.
IMO, the Power Post article was not really promotional. It mainly just
described the “whys” of the product design. I think it is an example of a
type of article that is apparently welcomed in the new Cycling Science
publication. To quote Jim Papadopoulus in a November 21 post: “My
impression is that there’s room, not only for strictly technical articles,
but for descriptions of ‘how we develop our products’ by manufacturers.”
IMO, such communications, and the discourse they will no doubt generate,
is healthy for everyone -- designers, developers, manufacturers, and
cyclists.
Ray Bowman
Ray Bowman
good lubricant for rubber. He responded by writing:
>Talc is not a lubricant. It is a release agent that prevents
>adhesion. An entirely clean tube will adhere to other smooth surfaces
>by its compliant and smooth surface, however, a tube already has mold
>release on its surface from manufacture. >snip<
and Thomas Kunich also responded by writing:
>Well, in my stupidity I would have thought that talc isn't a 'lubricant'
>of any kind at all. I would simply have assumed that talc in inserted
>to prevent rubber from contacting rubber and therefore prevent the
welding
>that occurs and also the high friction coefficient of rubber on rubber.
Yes, gents, talc is a good release agent for rubber and is widely used for
that purpose, but that does not mean that talc is not also a good dry
lubricant for rubber. Release agents are frequently also good lubricants.
If you squeeze two pieces of un-lubricated tube rubber together (outside
surfaces), they will have very high friction and it will be difficult to
make them slip against one another. This is often true, though less so,
even when there is mold release on the surfaces. If you then talc these
surfaces and again squeeze them together, you will note that the friction
is greatly reduced -- it is now slippery rather than grabby. Since a
lubricant is defined as a substance that reduces friction, talc is
obviously and unequivocally a good lubricant for rubber.
Jobst continued by writing:
>Ray Bowman writes:
>> While tire casings are fairly stiff, they do stretch significantly
>> (much more easily in some directions than in others). And powdered
>> talc happens to be a good lubricant for rubber, a fact widely known
>> both inside and outside the rubber industry. So, it may not require
>> much lateral force to cause a talced tube to slip.
>Because talc is not a lubricant, this will require substantial lateral
>force to move. Considering the rigidity of the casing in comparison
>to the tube, it should be apparent that for the minuscule distortion
>of the tire, the tube adapts easily as it works in-place. If you have
>looked at a tube that has been in the same tire without interruption
>(by removal for repair) you will have noticed that the casing cords
>and other features of the tire have fretted their images into the
>surface of the tube. This indicates that the tube remained indexed
>to the tire and that it was fretting. Talc has no effect on this
>phenomenon.
I, too, have noticed that various features of the tire often leave visible
markings on the tube. They are quite interesting. Some of the markings I
have seen were, IMO, due to adhesion between the tire and tube and result
from a stripping-off of surface residue from the tire or tube. But I have
also seen tire cord “images” and agree that these probably result from
fretting or nibbling. (Doesn’t such fretting or nibbling indicate
significant force and/or movement across the interface between the tire
and tube?) As you have noted, tube damage from fretting is fairly common
and occurs in a variety of ways, including from the edges of tire boots.
Tubes can also be fairly easily be nibbled through by the ends of broken
tire cords.
Since talc IS a good lubricant, neither large force nor large casing
stretch is required to cause movements between a talced tire and tube. I
think that little or negligible scrubbing is the usual condition because
many people use little or no talc. However, I also think it is possible
that not a lot of scrubbing is required to cause a significant increase in
rolling resistance. Since bike riders often spend considerable money to
make tiny improvements in cycling efficiency, even a small change in
rolling resistance is of interest.
Before you doubt the possible significance of tire-tube scrubbing, bear in
mind that typical tube casing material IS reasonably stretchy in some
directions and consider:
(a) Off-road bike riders often use their tires at pressures around 30
psi, and even considerably lower. IMO, These low pressures result in
considerable casing distortion as the tire rolls. Further, low pressures
force the tube against the tire much less than normal.
(b) It is fairly common to use undersized tubes. This questionable
practice is even recommended by some. Simple calculations show that the
tube stretch when using undersized tubes typically exceeds 100 % (that is,
the rubber stretches to two times the original dimension) and sometimes by
more than 150%. Because rubber stiffens when it is highly stretched, just
like any over-stretched spring, the effective stiffness of an undersized
tube expanded in a tire is considerably greater than normal. (Cut a strip
of rubber from a tube and put two marks across the width and one inch
apart along the length. Firmly clamp one end of the strip and position a
ruler alongside the free portion of the strip. Now pull the strip with
one hand until the marked length has first grown, in steps, first
slightly, then to roughly two, then three, and then four inches -- if the
strip does not break. At each stretch condition, use your other hand to
move the strip back and forth by small amounts to feel the effective
stiffness at that degree of stretch. You should easily be able to note an
increase in stiffness with increasing stretch. The tube rubber strips I
used increased in stiffness about three-fold, by my rough estimate, at the
three inch condition, and a lot at the four inch condition).
Don’t misunderstand me, Jobst. I have not said that I KNOW that tire-tube
scrubbing is a significant problem. I am making a quite reasonable
speculation that it COULD be. But that is not even my main motive in
these postings. My main interest is in clearing up some incorrect
reasoning about tires and tubes and the use of talc. My issue with you
here is that you have stated adamant conclusions about tire-tube scrubbing
that are based on false premises.
The only reliable way to be certain about tire-tube scrubbing is through
some careful, and probably difficult, measurements. If you would put
forth the interest, time, effort, and money to carry out these
measurements and to write a flawless report, you could probably get
published in Cycling Science. :-)
Ray Bowman
Jobst Brandt
> Your comments about later failures due to fretting strengthen my
> belief that no existing puncture-preventing product is very
> effective. I don't see how any armoring product can be truly
> effective in preventing punctures without adding so much stiffness
> and rolling resistance as to be very undesirable. I have believed
> this for a long time, which is why my own efforts have been to
> develop effective tube sealants. These can be, and a few actually
> are, highly effective for the great majority of tube failures.
That gets us down to a diminishing gap for puncture products.
Sealants, as well as the preventive products tested, have been on the
market for a substantial time. Their presence together with their
disuse give strong evidence of their impotence. Sealants have a
dangerous side to them that isn't mentioned often because those who
use them probably would not recognise the effect as being caused by
the sealant.
In the event of a flat with a sealant, such as a glass cut that spews
juice all over the following riders, the flattened tire becomes a
lubricated slide that is laterally uncontrollable. I have had this
experience and realize that had it been a front tire I would have
crashed at substantial speed. The road was straight and smooth with
minimal crown. In spite of the benign conditions, the bicycle went
into a fishtailing slide and was difficult to bring to a safe stop.
In contrast, I have ridden a blown out clincher with a dry tube, many
miles, with no steering problems whatsoever.
I think that, to make laboratory experiments useful, the full scope of
the problem being analyzed must be considered and test should simulate
reasonable subset of actual conditions. The outcome of the tests made
in Cycling Science were previously described in discussions on the
subject where it was pointed out that such devices merely increase the
depth of penetration required to pierce the tube. The "conclusions"
to the article took substantial space to obscure that point. What is
not known, is how much these devices increase rolling resistance for
their minimal protection. This information would have given the
report some redeeming value. So what did we learn for $7.00?
By the way, what was the cover picture "Force Pedal" (UC Davis) about?
I couldn't find the article to which it belonged.
Jobst Brandt <jbr...@hpl.hp.com>
Jobst Brandt
> If you squeeze two pieces of un-lubricated tube rubber together
> (outside surfaces), they will have very high friction and it will be
> difficult to make them slip against one another. This is often
> true, though less so, even when there is mold release on the
> surfaces. If you then talc these surfaces and again squeeze them
> together, you will note that the friction is greatly reduced -- it
> is now slippery rather than grabby. Since a lubricant is defined as
> a substance that reduces friction, talc is obviously and
> unequivocally a good lubricant for rubber.
Well then by that definition, sand is a good lubricant. Besides, I
think I explained that with the normal forces present (~120 psi) the
lateral force required for movement exceeds any lateral forces a tube
might bring to bear. The force required to stretch a tube a mm/mm2 is
about 100x less than the normal force.
> Since talc IS a good lubricant, neither large force nor large casing
> stretch is required to cause movements between a talced tire and
> tube. I think that little or negligible scrubbing is the usual
> condition because many people use little or no talc. However, I
> also think it is possible that not a lot of scrubbing is required to
> cause a significant increase in rolling resistance. Since bike
> riders often spend considerable money to make tiny improvements in
> cycling efficiency, even a small change in rolling resistance is of
> interest.
> Before you doubt the possible significance of tire-tube scrubbing,
> bear in mind that typical tube casing material IS reasonably
> stretchy in some directions and consider:
It is a typical bias oriented material (except Michelin) that allows
forming into a torus, and it can be lengthened or fattened but not
both. Therefore, it is not as though the casing can stretch as is
apparent from inflation to high pressure without a visible increase in
size but more an ability to make macro shape changes. If you think
there is significant scrubbing, then it might be appropriate to devise
an experiment to prove that contention. I see no evidence of anything
more than fretting, that by definition is less than a micrometer.
> Don't misunderstand me, Jobst. I have not said that I KNOW that
> tire-tube scrubbing is a significant problem. I am making a quite
> reasonable speculation that it COULD be. But that is not even my
> main motive in these postings. My main interest is in clearing up
> some incorrect reasoning about tires and tubes and the use of talc.
> My issue with you here is that you have stated adamant conclusions
> about tire-tube scrubbing that are based on false premises.
As you see, I am pursuing the same goal. I see no evidence that
significant scrubbing of tube against tire is occurring and that the
motion that occurs is energy absorbing. It shouldn't be difficult to
test though. By gluing the tube into the tire compared to talcum in
the tire, the rolling resistance should show that one is absorbing
more energy than the other. You are proposing that these things occur
so I think the ball is in your court.
> The only reliable way to be certain about tire-tube scrubbing is
> through some careful, and probably difficult, measurements. If you
> would put forth the interest, time, effort, and money to carry out
> these measurements and to write a flawless report, you could
> probably get published in Cycling Science.
I don't think I want my work appearing in Cycling Science under the
current circumstances. It reminds me of the Dr. Science series on my
local public radio station.
Jobst Brandt <jbr...@hpl.hp.com>
Eric Breitenberger
>Well, in my stupidity I would have thought that talc isn't a 'lubricant'
>of any kind at all. I would simply have assumed that talc in inserted
>to prevent rubber from contacting rubber and therefore prevent the welding
>that occurs and also the high friction coefficient of rubber on rubber.
Well, in *my* stupidity I would have thought that *grease* isn't a 'lubricant'
of any kind at all. I would simply have assumed that *grease* is inserted
to prevent *metal* from contacting *metal* and therefore prevent the welding
that occurs and also the high friction coefficient of *metal* on *metal*.
Cheers, Eric
Ray Bowman
Date: Mon, 9 Jan 1995 20:07:23 GMT
Jobst Brandt (J) writes:
>Ray Bowman writes:
R>> If you squeeze two pieces of un-lubricated tube rubber together
R>> (outside surfaces), they will have very high friction and it will be
R>> difficult to make them slip against one another. This is often
R>> true, though less so, even when there is mold release on the
R>> surfaces. If you then talc these surfaces and again squeeze them
R>> together, you will note that the friction is greatly reduced -- it
R>> is now slippery rather than grabby. Since a lubricant is defined as
R>> a substance that reduces friction, talc is obviously and
R>> unequivocally a good lubricant for rubber.
J> Well then by that definition, sand is a good lubricant. Besides, I
J> think I explained that with the normal forces present (~120 psi) the
J> lateral force required for movement exceeds any lateral forces a tube
J> might bring to bear. The force required to stretch a tube a mm/mm2 is
J> about 100x less than the normal force.
My definition is proper and is “standard”. In fact, sand does act as a
lubricant, as any cyclist or motorist knows who has skidded on a patch of
it. To some degree this is because the sand particles roll and otherwise
move or flow, and to some degree it is because the sand particles
individually can have a lower coefficient of resistance against the road
than tire rubber. There are a number of ways in which lubricants work --
fluid or greasy films are not the only kinds of lubricants. I happen to
have some finely divided silica (sand) and also some powdered plastic.
Both of these lubricate rubber substantially, though much less than does
talc. Part of talc’s lubricating effectiveness is because it is a very
soft material. Powdered graphite and Molybdenum Disulfide, two
commonly-used dry lubricants, also depend on being soft (easy to shear or
crush), though they have weak planes in their molecular structure only in
some directions.
You are on the right track in trying to be quantitative, but your
reasoning is still not sound because you have not factored in the obvious
fact that talc lubricates rubber quite well and that 120 psi is not the
only pressure to consider. I don’t know how to *realistically* analyse
the problem either, but I may try to provide an *improved* analysis in a
later post.
J [Tire casing]
J> is a typical bias oriented material (except Michelin) that allows
J>forming into a torus, and it can be lengthened or fattened but not
J>both. Therefore, it is not as though the casing can stretch as is
J>apparent from inflation to high pressure without a visible increase in
J>size but more an ability to make macro shape changes. If you think
J>there is significant scrubbing, then it might be appropriate to devise
J>an experiment to prove that contention. I see no evidence of anything
J>more than fretting, that by definition is less than a micrometer.
Stretch in the casing does not have to involve both “lengthening” and
“fattening”. IMO, the forces acting on the casing material can cause a
stretch in one direction at the expense of a shortening in another
direction. Either stretching or shortening can cause scrubbing. Both
happening simultaneously at more-or-less right angles should enhance any
tendency to scrubbing.
I am unaware of any definition of fretting that limits it to movements in
the micrometer range.
R>> Don't misunderstand me, Jobst. I have not said that I KNOW that
R>> tire-tube scrubbing is a significant problem. I am making a quite
R>> reasonable speculation that it COULD be. But that is not even my
R>> main motive in these postings. My main interest is in clearing up
R>> some incorrect reasoning about tires and tubes and the use of talc.
R>> My issue with you here is that you have stated adamant conclusions
R>> about tire-tube scrubbing that are based on false premises.
J> As you see, I am pursuing the same goal. I see no evidence that
J> significant scrubbing of tube against tire is occurring and that the
J> motion that occurs is energy absorbing. It shouldn't be difficult to
J> test though. By gluing the tube into the tire compared to talcum in
J> the tire, the rolling resistance should show that one is absorbing
J> more energy than the other. You are proposing that these things occur
J> so I think the ball is in your court.
You have the right basic idea about how the experiments could be
performed, but they are simple only “in principle”. There are many
experimental difficulties involved in rolling resistance measurements, and
values measured by various techniques often differ substantially and have
considerable “scatter” in the data. You would know these things if you
read Cycling Science [:-)]. Because the scrubbing effect, if it does
exist, is probably small, a very precise experimental method and
impeccable technique would be required to resolve the issue.
Perhaps significant tire-tube scrubbing does not occur under any normal
conditions -- I would not be surprised if this is so. But your adamant
belief that such scrubbing *can not* occur is actually a rank conjecture
because your reasoning has been unsound. I plan, within a few days, to
make some “quickie” measurements of effective tube stiffness; and this
should allow some improved estimates of the scrubbing possibility.
Ray Bowman