Tire Thread Count - What difference does it make?
Bestest Handsander
is the reason behind low and high threadcounts. What is considered a high
count anyway? If someone could point me to some reading material is would
be greatly appreciated.
jobst....@stanfordalumni.org
> I understand what a thread count is on bicycle tires, but what I
> don't know is the reason behind low and high thread counts. What is
> considered a high count anyway? If someone could point me to some
> reading material is would be greatly appreciated.
The fatter the casing cords the fewer there are per inch as in TPI or
threads-per-inch. The thicker the casing the greater the casing
stiffness and therefore the grater the rolling resistance. Rolling
resistance in tires is caused by flexing the tire casing, tube, and
tread... and in the case of a tubular tire, the viscous motion between
tire and rim in the rim glue.
If you look at the RR curves at:
http://www.terrymorse.com/bike/imgs/rolres.gif
You'll find characteristics of various tires. Tire brand and model is
immaterial but the shape of the curves isn't. As you can see, the
tire with the highest RR is also one that benefits the most from
higher inflation pressure but it never gets as good as the best. You
can almost estimate the TPI of the lower tires from their RR curves,
the best tires benefitting less from higher pressure than the thick
casing ones, that usually also have thicker tread.
Flexibility in tire casings goes parallel inversely with rolling
resistance.
Jobst Brandt
jobst....@stanfordalumni.org
carlfogel
Dear Asbestos,
A high count in a tire thread is probably anything over two dozen posts--
Oh, sorry, you mean tpi.
Jobst Brandt offered this reply to a comment:
[Marco suggested:]
>>>> So pick just about any tire with a high tpi count for durability
>>>> and puncture resistance,
[someone, possibly Jobst, inquired:]
>>> Would you say WHY you think this.
[Marco fantasized:]
>> Finer threads are weaker threads. They cannot be more durable ( look
>> at the Conti sidewall comments posted all the time for starters ) and
>> cannot be more puncture resistant unless the tread is stronger with
>> more resistant rubber components holding it into a casing.
[Jobst cleared up the confusion:]
> think you'll find that high TPI tires have uniformly higher burst
> pressures than the "kite string" tires. there may be exceptions but
> the fine cord is usually higher strength fiber than the fat cord cheap
> tires. the fine threads make a far thinner casing that flexes with
> little losses. This is apparent from rolling resistance curves that
> show high TPI tires have low rolling resistance and are relatively
> unaffected by inflation pressure (lots of flex to little flex). You
> can draw your own conclusions about individual brands and their side
> wall failures.
http://yarchive.net/bike/tire_cords.html
Apparently, fat-cord tires use cheap, weak, kite-string stuff. High tpi
tires use more expensive, stronger, thinner stuff that flexes with
little energy lost.
Think thin silk thread versus coarse cotton yarn, and you'll probably be
on the right track [pun].
Carl Fogel
--
Vizzutti
correct, but I'd add that a high thread count per inch also makes a huge
difference in comfort over cheap tires, at least with an aluminum frame.
Vortezza (sp?) has some 290 tpi tires on sale regularly for $20 if you
are looking. They are awesome.
--
Vizzutti
--
Paul Southworth
Bestest Handsander <no...@u.biz> wrote:
>I understand what a threadcount is on bicycle tires, but what I don't know
>is the reason behind low and high threadcounts. What is considered a high
>count anyway?
Low is often around 60 tpi; high more like 120+
--Paul
DRS
qXBac.97712$eD.9...@fe15.usenetserver.com
Is that a genuine 290tpi? For example, Continental routinely misrepresent
their thread counts because they add up the TPIs of all the carcass layers
of one tyre.
--
"I'm proud that I live in a country where witnessing two hours of bloody,
barbarous torture in gloating detail is considered indicia of religious
piety, whereas a mere second gazing upon a woman's breast is cause for
outraged apoplexy."
Betty Bowers, http://www.bettybowers.com/melgibsonpassion.html
Chalo
> The fatter the casing cords the fewer there are per inch as in TPI or
> threads-per-inch. The thicker the casing the greater the casing
> stiffness and therefore the grater the rolling resistance.
All else equal, a thin casing fabric will be more supple than a thick
one, and a high TPI fabric will be thicker than a low TPI fabric, but
that isn't the only pertinent variable, is it?
For instance, a high TPI tire with relatively thick or high-hysteresis
tread rubber would likely have higher RR than a low TPI tire with thin
or low-hysteresis rubber, wouldn't it?
Likewise, a multi-ply tire made of a fine casing fabric would tend to
have higher RR than a tire with a single pair of coarse plies, right?
I have suspected for some time that TPI is overrated as an indicator
of rolling resistance. I would like to find some authoritative
information to either confirm or refute my suspicion.
Chalo Colina
jobst....@stanfordalumni.org
>> The fatter the casing cords the fewer there are per inch as in TPI
>> or threads-per-inch. The thicker the casing the greater the casing
>> stiffness and therefore the grater the rolling resistance.
> All else equal, a thin casing fabric will be more supple than a
> thick one, and a high TPI fabric will be thicker than a low TPI
> fabric, but that isn't the only pertinent variable, is it?
Actually it is the opposite. The greater the TPI (threads per inch)
the thinner the cords and therefore the thinner the tire casing can
be. Since this requires a strong filament that is more expensive than
a coarse one, manufacturers who make high TPI tires generally don't
equip them with heavy, thick tread, just as one doesn't use huge
knobby SUV tires on a high performance sports car.
As I said, its the amount of elastomer and cord thickness that makes
the tire less pliable and therefore have more losses in bending, the
cause of rolling resistance.
> For instance, a high TPI tire with relatively thick or high-hysteresis
> tread rubber would likely have higher RR than a low TPI tire with thin
> or low-hysteresis rubber, wouldn't it?
That depends on how the casing is built but that is what I would expect
from such an unlikely combination.
> Likewise, a multi-ply tire made of a fine casing fabric would tend to
> have higher RR than a tire with a single pair of coarse plies, right?
Only if the casing were thicker assuming the tread and inner tube were
the same.
> I have suspected for some time that TPI is overrated as an indicator
> of rolling resistance. I would like to find some authoritative
> information to either confirm or refute my suspicion.
I think it is generally the best indicator. Clement made two tires on
the same casing. One was called Paris-Roubaix, the other Campionato
del Mundo. The Paris-Roubaix, being for a one day classic had a
narrower and thinner tread strip while the Campionato del Mundo, that
was designed for stage races over the Alps with mostly still unpaved
roads had a tread strip that went far up the sidewall and was nearly
twice as thick as that of the Paris-Roubaix in the center.
Avocet had a 23mm Criterium and TT tire on the same casing, also with
the thinner, lower RR tread on the TT.
For me the TPI tells me that I'm getting the lowest RR casing and the
tread thickness gives me durability. The two should not be confused.
Therefore, TPI IS the arbiter in the evaluation.
Jobst Brandt
jobst....@stanfordalumni.org
Chalo
> Chalo Colina writes:
>
> > All else equal, a thin casing fabric will be more supple than a
> > thick one, and a high TPI fabric will be thicker than a low TPI
> > fabric, but that isn't the only pertinent variable, is it?
>
> Actually it is the opposite. The greater the TPI (threads per inch)
> the thinner the cords and therefore the thinner the tire casing can
> be.
That's what I meant; I just said it backwards.
Thanks for the information.
Chalo Colina
andres muro
tell the difference. Also, I usually get about the same amount of
flats with both. When I buy a tire, I try to go for weight and price.
I hate to pay anything more than 12.00 bucks, so I look for sales. I
usually aim at about 260 to 300 grams tires anywhere between 23 and 25
width. If I can find a heavy tire with kevlar beads at this weight, I
go for them cause I assume the weight goes into the casing. Right now
I own some IRC triathlon with kevlar belts with 120 tpi, and some
victoria action tires with 66 tpi. They weigh close to 300 grams. I
can't tell any difference. However, I haven't tried to ride one after
the other to feel differences nor have I tried different PSI. I think
that I go just as fast. I have no problem keeping up with my friends
and making them hurt on flats, but as soon as we get to the hills,
they start dropping me like a rock. It doesn't matter what I am
riding or what tires I use. Oh, I've forgot, I used from latex to
heavy duty tubes, tubes with slime, and tubes surrounded by a second
tube. I can't tell the difference either. Right now, I stick to the
chepest butyl tube that I can find. I usually use tires until there is
nothing left. If a tire gets a big tear, I cut a plastic cup and use
the plastic to boot it. I get rid of tires when I have two or three
boots.
As you can see, my method of choosing and evaluating tires is very
scientific, of course.
Andres
cnhyf-10...@usenet.etext.org (Paul Southworth) wrote in message news:<OBIac.2031$WC3....@ord-read.news.verio.net>...
(Pete Cresswell)
>I assume the weight goes into the casing. Right now
>I own some IRC triathlon with kevlar belts with 120 tpi, and some
>victoria action tires with 66 tpi. They weigh close to 300 grams. I
>can't tell any difference.
Maybe its different for skinny high pressure tires.
I run 55/55 tires at about 35 psi. The ones I like best are 130 tpi WTB Mutano
Raptors. I've got another set that are 60 tpi (Heng Shin SemiSlicks).
The 130 tpi tires seem to roll a *lot* easier than the 60's - even on a paved
surface - and the 130's have a lot more tread on them.
OTOH, I'm one of those people who will swear that their car runs better after
being washed...so maybe my comparison isn't very scientific either...
--
PeteCresswell
jobst....@stanfordalumni.org
>> I assume the weight goes into the casing. Right now I own some IRC
>> triathlon with Kevlar belts with 120 TPI, and some Vittoria action
>> tires with 66 TPI. They weigh close to 300 grams. I can't tell any
>> difference.
> Maybe its different for skinny high pressure tires.
> I run 55/55 tires at about 35 psi. The ones I like best are 130 TPI
> WTB Mutano Raptors. I've got another set that are 60 TPI (Heng Shin
> SemiSlicks).
Kevlar is notorious for bad RR in tire casings and I'm not aware that
anyone is making a Kevlar tire , only Kevlar inlays as a belt under
the tread. Even these produce measurably poorer RR and that is why
they are so uselessly thin. They won't stop thorns either just as a
sewing needle will easily go through a bullet proof vest.
> The 130 TPI tires seem to roll a *lot* easier than the 60's - even
> on a paved surface - and the 130's have a lot more tread on them.
> OTOH, I'm one of those people who will swear that their car runs
> better after being washed...so maybe my comparison isn't very
> scientific either...
That's a good survey not to be ignored. Just ask the guy in his
freshly washed and waxed car if it doesn't feel a lot better.
Jobst Brandt
jobst....@stanfordalumni.org
Douglas Landau
> I own tires with 120 count and with 66 thread count. I really can't
> tell the difference. Also, I usually get about the same amount of
> flats with both. When I buy a tire, I try to go for weight and price.
> I hate to pay anything more than 12.00 bucks, so I look for sales.
I'm with you. Seems like there's a well-regarded tire on sale for
a great price often enough at either nasbar or performance that if
I buy four of them, I'm good until the next good deal comes along.
Right now I'm riding Panaracer Stradius Elites, which I think feel
stickier but also heavier and not quite as free-rolling than the
last sale tire I tried which was Michelin Hi-Lite Prestige. Gonna
order some of the $13 Conti 3000s on sale at performance right now.
I think Mike J said recently that people usually stick with whatever
came on their bike. Definately true of me. All I rode for the first
five years was Conti 2000s. I am now enjoying trying out different
tires -- but although it's fun and interesting, I have not yet found
any reason not to go back to the 2000s, which are nice and light and
always 20 bucks. Except possibly:
- Either it's my imagination or they slice on glass even more than
other tires (maybe just due to thin tread/light weight)
- I never see them on sale. (Can't imagine why :-)
-dkl
jobst....@stanfordalumni.org
>> I own tires with 120 count and with 66 thread count. I really can't
>> tell the difference. Also, I usually get about the same amount of
>> flats with both. When I buy a tire, I try to go for weight and
>> price. I hate to pay anything more than 12.00 bucks, so I look for
>> sales.
> I'm with you. Seems like there's a well-regarded tire on sale for a
> great price often enough at either Nashbar or performance that if I
> buy four of them, I'm good until the next good deal comes along.
Oh but there is another side to this. A low TPI tire run at high
pressure will sustain broken cords when rolling over angular obstacles
(1/2" piece of rock) and show only a distortion in the tread. The
casing being bias ply and only the inner layer fails in such bending,
a zig-zag in the tread pattern (if there is one) is the only subtle
indicator. In ant case, the blowout may come later. This was also
true in tubular days when some riders bought "kite string"
Clement-50's instead of 120TPI silks. The 50 was called a good
training tire... which it wasn't. What a slug, too.
> Right now I'm riding Panaracer Stradius Elites, which I think feel
> stickier but also heavier and not quite as free-rolling than the
> last sale tire I tried which was Michelin Hi-Lite Prestige. Gonna
> order some of the $13 Conti 3000s on sale at performance right now.
I guess that depends on what you do with them. Just cruising on
smooth pavement shouldn't cause any problems.
Jobst Brandt
jobst....@stanfordalumni.org
Douglas Landau
> Douglas Landau writes:
>
> >> I own tires with 120 count and with 66 thread count. I really can't
> >> tell the difference. Also, I usually get about the same amount of
> >> flats with both. When I buy a tire, I try to go for weight and
> >> price. I hate to pay anything more than 12.00 bucks, so I look for
> >> sales.
>
> > I'm with you. Seems like there's a well-regarded tire on sale for a
> > great price often enough at either Nashbar or performance that if I
> > buy four of them, I'm good until the next good deal comes along.
>
> Oh but there is another side to this. A low TPI tire run at high
> pressure will sustain broken cords when rolling over angular obstacles
> (1/2" piece of rock) and show only a distortion in the tread. The
> casing being bias ply and only the inner layer fails in such bending,
> a zig-zag in the tread pattern (if there is one) is the only subtle
> indicator. In ant case, the blowout may come later. This was also
> true in tubular days when some riders bought "kite string"
> Clement-50's instead of 120TPI silks. The 50 was called a good
> training tire... which it wasn't. What a slug, too.
Interesting.
I was unclear in the way I quoted Andreas. I did not intend to comment
on thread count. I was agreeing with how much he likes to spend and
his strategy of looking for sales.
> > Right now I'm riding Panaracer Stradius Elites, which I think feel
> > stickier but also heavier and not quite as free-rolling than the
> > last sale tire I tried which was Michelin Hi-Lite Prestige. Gonna
> > order some of the $13 Conti 3000s on sale at performance right now.
>
> I guess that depends on what you do with them. Just cruising on
> smooth pavement shouldn't cause any problems.
The Stradius elites are 126 TPI. My only experience with TPI is having
bought some 33 TPI Michelins. I hated them. They were hard as a rock
and slugs. I would not buy a tire with anything less than 120 after that.
dkl
John Roden
Armadillo. They are virtually impossible to flat because they are so
thick, but going downhill they roll much slower than regular old
tires. I tried swapping wheels on a training ride with a friend and
whoever had the Armadillos would end up loosing a bike length every 50
or so meters.
I use these tires because they are so tough, but always assumed the
very rigid casing is what caused them to roll so slowly--am I correct
in this assumption?
carlfogel
Dear John,
Actually, an incredibly rigid and resilient casing (like steel) would
reduce rolling resistance. Little beyond magnetic levitation beats
steel railroad car wheels on steel rails for low rolling resistance.
(This is why no one worries about the rolling resistance of the
bicycle's hub bearings--the metal rolling resistance is infinitesimal
compared to the clumsy tires.)
Given plenty of air pressure (a marvelous spring), the same material
(rubber isn't as good as latex), and the same smooth tread (any pattern
increases rolling resistance by allowing extra squirm), what matters is
how thick the tread is and how high the loss is in the casing--the
thinner, the better.
Basically, the less material that you flex into an endless bulge as the
tire meets the road, the less energy you waste distorting it. This is
the real advantage of light tires and light tubes, the latter becoming
part of the tire under normal pressures.
Some materials absorb more energy as they flex (rubber versus latex, for
example), but the big problem with your tires is likely just that
there's so much of them. Big soggy chunks of rubber, kevlar, and cotton
with block treads squirming uselessly to the sides don't roll as well as
thin, smooth wafers of highly pressurized latex and silk.
With luck, more learned types will expound on the details and correct
any misconceptions.
Carl Fogel
--
(Pete Cresswell)
>Basically, the less material that you flex into an endless bulge as the
>tire meets the road, the less energy you waste distorting it. This is
>the real advantage of light tires and light tubes, the latter becoming
>part of the tire under normal pressures.
As long as the road is smooth....
--
PeteCresswell
Vizzutti
misrepresent their thread counts because they add up the TPIs of all the
carcass layers of one tyre.
Yes, I believe so. However, the 290 TPI was not for clinchers. The ones
I got were 220 TPI. I remembered wrong!
To do as you say and add up plys is very irresponsible. Threads-per-inch
should be just what it says.
Check these tires out. They are on sale for $25, they are lighter than
Michelin Pro Race, have 220 tpi and you will know the difference over
low tpi tires, if your frame doesn't absorb the shock. It was night and
day on an aluminum bike. I have 2,000 miles on these with not a single
flat (and I do occasionally run over glass.)
http://www.performancebike.com/shop/Profile.cfm?SKU=17216
To others, imagine your forward momentum as a horizontal vector. With
stiff tires (low tpi), when you hit a bump, the front end of your bike
lifts up, converting the horizontal momentum to an upward force which
never is reconverted to forward motion. The upward motion transmits
throughout the frame into your hands and muscles. This is rolling
resistance.
A supple high tpi tire will deform and although the flex of the tires
absorb some energy and equals heat loss, the energy wasted is minor
compared to what is transmitted into your body from hard tires.
What goes on over a bump goes on constantly over asphalt. High tpi tires
give the best of both worlds: comfort and low rolling resistance.
--
BaCardi
> Basically, the less material that you flex into an endless bulge as the
> tire meets the road, the less energy you waste distorting it. This is
> the real advantage of light tires and light tubes, the latter becoming
> part of the tire under normal pressures.
> Some materials absorb more energy as they flex (rubber versus latex, for
> example), but the big problem with your tires is likely just that
> there's so much of them. Big soggy chunks of rubber, kevlar, and cotton
> with block treads squirming uselessly to the sides don't roll as well as
> thin, smooth wafers of highly pressurized latex and silk.
I like this line of reasoning. However, if you are saying that stiffer
tires = less rolling resistance due to less footprint where the tire
rubber meets the road, then why would lighter thinner casing tires such
as those with higher TPI count = less rolling resistance? Wouldn't you
get more rolling resistance due to the thinner tire deforming more under
the rider's weight and hence a bigger footprint where the tire rubber
meets the road?
--
Adam Rush
> heavy duty tubes, tubes with slime, and tubes surrounded by a second
> tube. I can't tell the difference either. Right now, I stick to the
> chepest butyl tube that I can find. I usually use tires until there is
> nothing left. If a tire gets a big tear, I cut a plastic cup and use
> the plastic to boot it. I get rid of tires when I have two or three
> boots.
On that note, my commuter bikes have next to always been old 27"
ten-speeds. I use those thick, thorn-resistant tubes because, when
they do flat, they allow me to keep riding to my destination before I
do something about it. Run-flat, if you will.
ZeeExSixAre
> throughout the frame into your hands and muscles. This is rolling
> resistance.
?????
--
Phil, Squid-in-Training
John Retchford
> I like this line of reasoning. However, if you are saying that stiffer
> tires = less rolling resistance due to less footprint where the tire
> rubber meets the road, then why would lighter thinner casing tires such
> as those with higher TPI count = less rolling resistance? Wouldn't you
> get more rolling resistance due to the thinner tire deforming more under
> the rider's weight and hence a bigger footprint where the tire rubber
> meets the road?
You miss two of Carl’s points. The first has to do with the nature of
the materials. In the railway wheel analogy the steel is behaving
elastically at the contact patch – it is being loaded and unloaded along
the same (linear) path in the load versus elongation plot. As work is
force times the distance the force moves, no net work is being done.
In the case of the bicycle tyre, you are dealing with an anelastic
material. Because its force vs elongation characteristic exhibits
hysteresis, work must be done on it during loading and unloading. The
rate of doing work is power and this power comes from the rider’s legs.
The area of the contact patch of a tyre is almost solely a function of
force on the tyre (the weight) and its pressure. This just comes from
the definition of pressure (force/area). The force supported by the
sidewalls is negligible for a feasible bicycle tyre. Try pressing a
fully deflated tyre with your thumb. So the thick walled tyre will have
essentially the same contact patch area as its thin walled counterpart
and will absorb more of the rider’s power in hysteresis loss as its
walls deform as it rolls along. Just like Carl said.
John Retchford
--
BaCardi
> You miss two of Carl’s points. The first has to do with the nature of
> the materials. In the railway wheel analogy the steel is behaving
> elastically at the contact patch – it is being loaded and unloaded along
> the same (linear) path in the load versus elongation plot. As work is
> force times the distance the force moves, no net work is being done.
> In the case of the bicycle tyre, you are dealing with an anelastic
> material. Because its force vs elongation characteristic exhibits
> hysteresis, work must be done on it during loading and unloading. The
> rate of doing work is power and this power comes from the rider’s legs.
> The area of the contact patch of a tyre is almost solely a function of
> force on the tyre (the weight) and its pressure. This just comes from
> the definition of pressure (force/area). The force supported by the
> sidewalls is negligible for a feasible bicycle tyre. Try pressing a
> fully deflated tyre with your thumb. So the thick walled tyre will have
> essentially the same contact patch area as its thin walled counterpart
> and will absorb more of the rider’s power in hysteresis loss as its
> walls deform as it rolls along. Just like Carl said.
> John Retchford
Alright, then I must be still missing the two points you say, because
after a review I still don't understand it. If a tire's contact is
alsmost "solely a function of force on the tyre (the weight) and its
pressure" like you say, then what difference does TPI have to do with
it? That's what we've all been discussing to date.
--
Douglas Landau
> .... However, if you are saying that stiffer
> tires = less rolling resistance due to less footprint where the tire
> rubber meets the road, then why would lighter thinner casing tires such
> as those with higher TPI count = less rolling resistance? Wouldn't you
> get more rolling resistance due to the thinner tire deforming more under
> the rider's weight and hence a bigger footprint where the tire rubber
> meets the road?
How much footprint there is depends upon the PSI to which the tire is
inflated, not how stiff it is. If the tires are inflated to 20PSI,
and the bike+rider weigh 200 lbs, then the tires are going to lay
down ten square inches of rubber, no matter what.
dl
ZeeExSixAre
> force on the tyre (the weight) and its pressure. This just comes from
> the definition of pressure (force/area). The force supported by the
> sidewalls is negligible for a feasible bicycle tyre. Try pressing a
> fully deflated tyre with your thumb. So the thick walled tyre will have
> essentially the same contact patch area as its thin walled counterpart
> and will absorb more of the rider's power in hysteresis loss as its
> walls deform as it rolls along. Just like Carl said.
Wow, this is cool - I know what you're talking about, hysteresis and such.
(I'm a college student studying mechanical engineering) What I don't get is
whether the thick-sidewall tire has more or less rolling resistance compared
to the thin-walled tire.
--
Phil, Squid-in-Training
BaCardi
Yes, but a thinner tire leads to greater deformation under load and thus
a larger contact area with the road. Greater contact area with road =
greater rolling resistance.
--
John Retchford
> > The area of the contact patch of a tyre is almost solely a function of
> > force on the tyre (the weight) and its pressure. This just comes from
> > the definition of pressure (force/area). The force supported by the
> > sidewalls is negligible for a feasible bicycle tyre. Try pressing a
> > fully deflated tyre with your thumb. So the thick walled tyre will
> > have essentially the same contact patch area as its thin walled
> > counterpart and will absorb more of the rider's power in hysteresis
> > loss as its walls deform as it rolls along. Just like Carl said.
> Wow, this is cool - I know what you're talking about, hysteresis and
> such. (I'm a college student studying mechanical engineering) What I
> resistance compared to the thin-walled tire.
The thick walled tyre will have more rolling resistance than the thin
walled one, other things being equal. The rider must do more work on the
walls in the region of the rolling contact patch to deform them.
John Retchford
--
jobst....@stanfordalumni.org
>> I like this line of reasoning. However, if you are saying that
>> stiffer tires = less rolling resistance due to less footprint where
>> the tire rubber meets the road, then why would lighter thinner
>> casing tires such as those with higher TPI count = less rolling
>> resistance? Wouldn't you get more rolling resistance due to the
>> thinner tire deforming more under the rider's weight and hence a
>> bigger footprint where the tire rubber meets the road?
> You miss two of Carl's points. The first has to do with the nature
> of the materials. In the railway wheel analogy the steel is
> behaving elastically at the contact patch? it is being loaded and
> unloaded along the same (linear) path in the load versus elongation
> plot. As work is force times the distance the force moves, no net
> work is being done.
Steel isn't entirely without losses and that is why, for instance, a
loaded rail car cannot be pushed by hand on a level track with
trivial. Part of that is cause by sag in the rail, placing the car's
wheels in depressions and the rest is hysteretic losses in steel.
There are losses in steel just as there are looses in tires.
> In the case of the bicycle tyre, you are dealing with an elastic
> material. Because its force vs elongation characteristic exhibits
> hysteresis, work must be done on it during loading and unloading.
> The rate of doing work is power and this power comes from the
> rider's legs.
Let's not get the rider involved in RR of bicycle tires. That only
clouds the matter. It might be worth mentioning that hysteresis is
the characteristic by which some of the force that deformed the
material is not returned as force on rebound but generates heat. High
temper steels have little hysteresis compared to mild steel while
rubber has far greater losses. Typically a toy monkey hanging on a
steel spring and a rubber band, the one on the rubber band will stop
bouncing long before the one on steel comes to rest.
> The area of the contact patch of a tyre is almost solely a function
> of force on the tyre (the weight) and its pressure. This just comes
> from the definition of pressure (force/area). The force supported
> by the sidewalls is negligible for a feasible bicycle tyre. Try
> pressing a fully deflated tyre with your thumb. So the thick walled
> tyre will have essentially the same contact patch area as its thin
> walled counterpart and will absorb more of the rider's power in
> hysteresis loss as its walls deform as it rolls along. Just like
> Carl said.
Well, "AS Carl said" but the reasons for low TPI tires having greater
losses than high TPI tires has been discussed here at great length,
recently. Maybe a GOOGLE search would help. In any case, there is an
FAQ abut this at:
http://draco.acs.uci.edu/rbfaq/FAQ/8b.14.html
Jobst Brandt
jobst....@stanfordalumni.org
jobst....@stanfordalumni.org
>> I like this line of reasoning. However, if you are saying that
>> stiffer tires = less rolling resistance due to less footprint where
>> the tire rubber meets the road, then why would lighter thinner
>> casing tires such as those with higher TPI count = less rolling
>> resistance? Wouldn't you get more rolling resistance due to the
>> thinner tire deforming more under the rider's weight and hence a
>> bigger footprint where the tire rubber meets the road?
> You miss two of Carl's points. The first has to do with the nature
> of the materials. In the railway wheel analogy the steel is
> behaving elastically at the contact patch? it is being loaded and
> unloaded along the same (linear) path in the load versus elongation
> plot. As work is force times the distance the force moves, no net
> work is being done.
Steel isn't entirely without losses and that is why, for instance, a
loaded rail car cannot be pushed by hand on a level track. Part of
that is cause by sag in the rail, placing the car's wheels in
depressions while the rest is hysteretic losses in steel. There are
losses in steel just as there are looses in tires.
> In the case of the bicycle tyre, you are dealing with an elastic
> material. Because its force vs elongation characteristic exhibits
> hysteresis, work must be done on it during loading and unloading.
> The rate of doing work is power and this power comes from the
> rider's legs.
Let's not get the rider involved in RR of bicycle tires. That only
clouds the matter. It might be worth mentioning that hysteresis is
the characteristic by which some of the force that deformed the
material is not returned as force on rebound but generates heat. High
temper steels have little hysteresis compared to mild steel while
rubber has far greater losses. Typically a toy monkey hanging on a
steel spring and a rubber band, the one on the rubber band will stop
bouncing long before the one on steel comes to rest.
> The area of the contact patch of a tyre is almost solely a function
> of force on the tyre (the weight) and its pressure. This just comes
> from the definition of pressure (force/area). The force supported
> by the sidewalls is negligible for a feasible bicycle tyre. Try
> pressing a fully deflated tyre with your thumb. So the thick walled
> tyre will have essentially the same contact patch area as its thin
> walled counterpart and will absorb more of the rider's power in
> hysteresis loss as its walls deform as it rolls along. Just like
> Carl said.
Well, "AS Carl said" but the reasons for low TPI tires having greater
Ted Bennett
> Douglas Landau wrote:
> > How much footprint there is depends upon the PSI to which the tire is
> > inflated, not how stiff it is. If the tires are inflated to 20PSI, and
> > the bike+rider weigh 200 lbs, then the tires are going to lay down ten
> > square inches of rubber, no matter what.
>Yes, but a thinner tire leads to greater deformation under load and thus
> a larger contact area with the road. Greater contact area with road =greater
> rolling resistance.
You might want to go back and read what Doug is patiently trying to
explain to you.
The area of the contact patch is determined by the pressure in the tire
and the weight carried.
--
Ted Bennett
Portland OR
BaCardi
OK, and your premise is based on the area of contact patch IS determined
by the pressure in the tire and weight. Right? So, so basically what you
and Doug are saying is not the same as what Jobst patiently explained. I
think you ought to go back and read what Jobst is saying.
--
Jay Hill
>
> How much footprint there is depends upon the PSI to which the tire is
> inflated, not how stiff it is. If the tires are inflated to 20PSI,
> and the bike+rider weigh 200 lbs, then the tires are going to lay
> down ten square inches of rubber, no matter what.
>
footprint as one of my 700c x 23mm bike tires if they're both inflated
to the same psi & have the same weight pressing down on them?
Sheldon Brown
>>
>> How much footprint there is depends upon the PSI to which the tire is
>> inflated, not how stiff it is. If the tires are inflated to 20PSI,
>> and the bike+rider weigh 200 lbs, then the tires are going to lay
>> down ten square inches of rubber, no matter what.
Jay Hill wrote:
> So one of my car tires, which are about 10" wide, will leave the same
> footprint as one of my 700c x 23mm bike tires if they're both inflated
> to the same psi & have the same weight pressing down on them?
That's basically correct. It's a bit slippery because the appropriate
pressures are so different. If you actually were to run a 23 mm tire at
20 psi, it would bottom out on the rim, so pneumatic effects would
disappear.
However, if you were to pump up your 10" wide car tires to 100 psi, and
to load each tire with a 100 pounds, you'd get a contact patch 10 inches
wide and 1 inch front to back.
This is true in theory. In practice, a tire with a thicker, stiffer
tread may have a slightly smaller contact patch (and slightly higher
average pressure against the pavement) due to the stiffness of the tire
not permitting it to completely conform. Thus, your car tires, in
practice, would actually have a slightly _smaller_ contact patch than
your bike tires, for the same pressure and loading.
Sheldon "Counterintuitive" Brown
+-----------------------------------------------+
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| April 9-10,15-17 http://web.mit.edu/gsp/www |
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+-----------------------------------------------+
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Phone 617-244-9772 FAX 617-244-1041
http://harriscyclery.com
Hard-to-find parts shipped Worldwide
http://captainbike.com http://sheldonbrown.com
Terry Morse
> What I don't get is whether the thick-sidewall tire has more or less
> rolling resistance compared to the thin-walled tire.
The thick-sidewall tire has more rolling resistance, because more
viscoelastic material is deformed as it is loaded and unloaded.
--
terry morse Palo Alto, CA http://bike.terrymorse.com/
Douglas Landau
Sure, at least in the clean case. I admit that not all cases are clean.
In fact, the case in which I frst read what I was quoting is itself not
clean.
What I wrote, I quoted straight from "the Boonie Book", a book about
dirtbiking from the 70s which I had when I was a kid. The author said
that about dirtbike tires, addressing the issue of whether a rider riding
sideways across a slope should weight the uphill peg or the downhill peg
for best traction. The author claimed that it does not matter, and that
was his reasoning.
However, I say that in fact, if you park your dirtbike on clean rock, you
will see that in fact only a few knobs of each tire are touching the rock,
nowhere near the number of square inches of rubber which should be according
to the theory.
So, the contactPatch=Load/PSI formula is too simplistic to be absolutely
correct. Bacardi is right, to some extent. I should have truncated the
"no matter what". That said, the case of roadbike tires is a pretty clean
case.
Doug
Douglas Landau
Sure, at least in the clean case. I admit that not all cases are clean.
jobst....@stanfordalumni.org
Well that's a bad example because bare tire, no rim, no inflation, can
support a person's full weight a because it is so rigid. Most of us
at one time or another sat on such a tire at an auto shop or played on
a swing made of an old tire.
In theory the idea is correct but practically automotive tires don't
have enough compliance to behave that way with small loads.
Jobst Brandt
jobst....@stanfordalumni.org
jobst....@stanfordalumni.org
>>> How much footprint there is depends upon the PSI to which the tire
>>> is inflated, not how stiff it is. If the tires are inflated to
>>> 20PSI, and the bike+rider weigh 200 lbs, then the tires are going
>>> to lay down ten square inches of rubber, no matter what.
>> So one of my car tires, which are about 10" wide, will leave the
>> same footprint as one of my 700c x 23mm bike tires if they're both
>> inflated to the same psi & have the same weight pressing down on
>> them?
> Sure, at least in the clean case. I admit that not all cases are
> clean. In fact, the case in which I first read what I was quoting is
> itself not clean.
> What I wrote, I quoted straight from "the Boonie Book", a book about
> dirtbiking from the 70s which I had when I was a kid. The author
> said that about dirtbike tires, addressing the issue of whether a
> rider riding sideways across a slope should weight the uphill peg or
> the downhill peg for best traction. The author claimed that it does
> not matter, and that was his reasoning.
Clean or dirty, on what foot you stand has something to do with side
slope pedal clearance but nothing to do with traction. Let's not get
all crossed up here.
> However, I say that in fact, if you park your dirtbike on clean
> rock, you will see that in fact only a few knobs of each tire are
> touching the rock, nowhere near the number of square inches of
> rubber which should be according to the theory.
Oh piss! That's like saying when you ride over a metal mesh the
contact patch is only 1/10 or the like. You can also balance a
bicycle on the head of a nail with less than 1/10 square inch area.
The same goes for a contact patch on a chip-seal road.
Contact patch in this context means what the flattened area of the tire
that presses against the road is, not what the actual intimate material
contact is. If you want to go into that, true contact, as is used in
tribology, is a difficult area to define.
> So, the contactPatch=Load/PSI formula is too simplistic to be
> absolutely correct. Bacardi is right, to some extent. I should
> have truncated the "no matter what". That said, the case of
> roadbike tires is a pretty clean case.
Don't be such a sophist, contact patch is a valid term for bicycle
tires on smooth surfaces. The area of that patch is governed by
inflation pressure. Odd surfaces of tire or road don't fit into that
description. That smooth tread has finally arrived with bicycles took
so long because the most recalcitrant technical conservatives are
found among bicyclists.
Jobst Brandt
jobst....@stanfordalumni.org
jobst....@stanfordalumni.org
> However, I say that in fact, if you park your dirtbike on clean
> rock, you will see that in fact only a few knobs of each tire are
> touching the rock, nowhere near the number of square inches of
> rubber which should be according to the theory.
> So, the contactPatch=Load/PSI formula is too simplistic to be
> absolutely correct. Bacardi is right, to some extent. I should
> have truncated the "no matter what". That said, the case of
> roadbike tires is a pretty clean case.
You might also consider this:
http://draco.acs.uci.edu/rbfaq/FAQ/8b.25.html
Jobst Brandt
jobst....@stanfordalumni.org
Tom
I am foolish to enter into a discussion re how many angels can dance
on the head of a pin so I shall just throw this in and back quickly
towards the door....
I offer the following as nothing more than a backyard experiment, but
might be food for thought.
http://www.tomschmitz.org/Contact%20PatchFrame1Source1.htm
Regards,
Tom
Ted Bennett
I don't see any disagreement between Jobst and me in this case.
jobst....@stanfordalumni.org
>> The area of the contact patch is determined by the pressure in the
>> tire and the weight carried.
> I am foolish to enter into a discussion re how many angels can dance
> on the head of a pin so I shall just throw this in and back quickly
> towards the door....
> I offer the following as nothing more than a backyard experiment,
> but might be food for thought.
> http://www.tomschmitz.org/Contact%20PatchFrame1Source1.htm
That's too bad that the test was done with a tire that had a thick and
clefted tread rubber that squirmed in a way that did not represent the
contact patch that would appear if a light weight road tire had been
used. This experiment was like stepping on a jellyfish and measuring
contact area. The contact patch of a toroidal shaped tire is a canoe
form. This one was not.
Jobst Brandt
jobst....@stanfordalumni.org
Tom Schmitz
<jobst....@stanfordalumni.org> wrote in message
news:9blfc.5773$Fo4....@typhoon.sonic.net...
> Tom Schmitz writes:
>
> > I offer the following as nothing more than a backyard experiment,
> > but might be food for thought.
>
> > http://www.tomschmitz.org/Contact%20PatchFrame1Source1.htm
>
> That's too bad that the test was done with a tire that had a thick and
> clefted tread rubber that squirmed in a way that did not represent the
> contact patch that would appear if a light weight road tire had been
> used. This experiment was like stepping on a jellyfish and measuring
Jobst -
The tire in question, when new, weighed in at about 220 grams. The tread was
not unusually thick.
The "clefted tread" you refer to is nothing more than typically useless
rain siping.
> contact area. The contact patch of a toroidal shaped tire is a canoe
> form. This one was not.
I would like to see pictures of such a shape if you can provide them. I
would agree that one might
expect a canoe shape of a new tire's imprint, but what of a tire that has
1500 miles of use? Such a tire
will not have a perfectly toroidal shape as there will be a flat wear
pattern in the center of the tread.
Even so, I should think that this would not have an effect on the area of
the contact patch, only it's shape.
I shall find it personally enlightening to be able to do the test over with
new tires, in various sizes, in a more
controlled fashion. This I hope to be able to do quite soon as I have
everything I need except a round tuit.
Regards,
Tom
BaCardi
Foolish! Try again! Re-read the paragraphs on the characteristics by
force that deformed the material is not returned.
--
jobst....@stanfordalumni.org
>>> I offer the following as nothing more than a backyard experiment,
>>> but might be food for thought.
http://www.tomschmitz.org/Contact%20PatchFrame1Source1.htm
>> That's too bad that the test was done with a tire that had a thick
>> and clefted tread rubber that squirmed in a way that did not
>> represent the contact patch that would appear if a light weight
>> road tire had been used. This experiment was like stepping on a
>> jellyfish and measuring...
> The tire in question, when new, weighed in at about 220 grams. The
> tread was not unusually thick. The "clefted tread" you refer to is
> nothing more than typically useless rain siping.
>> ... contact area. The contact patch of a toroidal shaped tire is a
>> canoe form. This one was not.
> I would like to see pictures of such a shape if you can provide
> them. I would agree that one might expect a canoe shape of a new
> tire's imprint, but what of a tire that has 1500 miles of use? Such
> a tire will not have a perfectly toroidal shape as there will be a
> flat wear pattern in the center of the tread.
Oh! The tire was worn flat. That means its unloaded contact area is
already fairly large and need hardly deform to make a fairly large
stamp pad mark on paper. That is to be expected since that area is
somewhat independent of inflation pressure.
> Even so, I should think that this would not have an effect on the
> area of the contact patch, only it's shape. I shall find it
> personally enlightening to be able to do the test over with new
> tires, in various sizes, in a more controlled fashion. This I hope
> to be able to do quite soon as I have everything I need except a
> round tuit.
I did my tests with a new round cross section smooth tire. Since the
tread rubber has an obvious stiffness, the area of that patch,
although canoe shaped did not match inflation pressure better than by
eyeball. The only tire that will accurately reflect that would be a
less than 120 gram track tubular. Above that other effects change the
shape and size of the contact as you demonstrate while tread stiffness
reduces contact of a smooth tread round cross section tire. In that
case contact pressure is not uniform across the area but higher in the
center due to bending forces.
In any case, the compliance of the tire being constant, inflation
pressure has the effects described although in practice they may not
be exactly the computed ones of thin walled round cross section tires.
The trend is accurate for traction purposes.
Car tires, in contrast, are mostly radial and therefore belted. Belts
can give a broad, non-circular cross section as you can see on many
cars that allude to being race cars in disguise.
Jobst Brandt
jobst....@stanfordalumni.org
Douglas Landau
Ok, fine. I used "footprint" when responding to Bacardi, when I
should have used "contact patch". Then I used "contact patch" when
responding to Jay when I should have used "footprint".
> > So, the contactPatch=Load/PSI formula is too simplistic to be
> > absolutely correct. Bacardi is right, to some extent. I should
> > have truncated the "no matter what". That said, the case of
> > roadbike tires is a pretty clean case.
>
> Don't be such a sophist, contact patch is a valid term for bicycle
> tires on smooth surfaces. The area of that patch is governed by
> inflation pressure.
Now -there's- the pot calling the kettle black! In any case, you are
agreeing with me here, as you do again in your next post where you write
>Well that's a bad example because ...
Doug
Tom Schmitz
<jobst....@stanfordalumni.org> wrote in message
news:0_mfc.5777$Fo4....@typhoon.sonic.net...
> Tom Schmitz writes:>
> > I would like to see pictures of such a shape if you can provide
> > them. I would agree that one might expect a canoe shape of a new
> > tire's imprint, but what of a tire that has 1500 miles of use? Such
> > a tire will not have a perfectly toroidal shape as there will be a
> > flat wear pattern in the center of the tread.
>
> Oh! The tire was worn flat. That means its unloaded contact area is
> already fairly large and need hardly deform to make a fairly large
> stamp pad mark on paper. That is to be expected since that area is
> somewhat independent of inflation pressure.
Indeed, it is. I wish that I had possessed the presence of mind to record
the imprint of that tire with no load on it. That would have been a good
baseline. I shall remember that in the next go-round.
>
> > Even so, I should think that this would not have an effect on the
> > area of the contact patch, only it's shape. I shall find it
> > personally enlightening to be able to do the test over with new
> > tires, in various sizes, in a more controlled fashion. This I hope
> > to be able to do quite soon as I have everything I need except a
> > round tuit.
>
> I did my tests with a new round cross section smooth tire. Since the
> tread rubber has an obvious stiffness, the area of that patch,
> although canoe shaped did not match inflation pressure better than by
> eyeball. The only tire that will accurately reflect that would be a
> less than 120 gram track tubular. Above that other effects change the
> shape and size of the contact as you demonstrate while tread stiffness
> reduces contact of a smooth tread round cross section tire. In that
> case contact pressure is not uniform across the area but higher in the
> center due to bending forces.
>
> In any case, the compliance of the tire being constant, inflation
> pressure has the effects described although in practice they may not
> be exactly the computed ones of thin walled round cross section tires.
> The trend is accurate for traction purposes.
>
This is the part that interests me. I would like to see what happens with
brand new tires, identical except for section width. The tires I could
afford to accumulate are not top of the line, but they are what one would
call light road tires - in the range of 220-230 grams - that one would
actually ride on daily. Unfortunately, they are siped. I have some Michelin
Hi-Lites (smooth tread) in a couple of section widths, but the construction
of that tire is unique with its woven carcass.
I no longer have a wheel to mount sew-ups on, though I could build one from
junque-at-hand. My pile of tubulars, though, is very short and doesn't
include anything in the track category.
Regards,
Tom
dvt
> I offer the following as nothing more than a backyard experiment, but
> might be food for thought.
>
> http://www.tomschmitz.org/Contact%20PatchFrame1Source1.htm
Nice piece of work. I think the results are a little bit off, but your
basic experiment is neat.
It seems to me that the act of mounting a bike would cause the wheel to
roll fore and aft slightly as well as rocking from side to side. Any
motion would cause the contact area measurement to be exaggerated. In
addition, you may load the front tire more heavily than the nominal
value momentarily during the mounting process.
I'm not convinced that the contact patch is 2 x Load/Presure with a
"light road tire." The stiffness of the casing may make the contact
patch slightly greater than L/P (i.e. 5-10%), but I'd be very surprised
to see a factor of two.
And by the way, the ideal gas law has nothin' to do with it. You could
have an incompressible fluid in your tire and the balance of force would
still predict the same contact area for a given pressure.
--
Dave
dvt at psu dot edu
Tom Schmitz
> Tom wrote:
>
>> I offer the following as nothing more than a backyard experiment, but
>> might be food for thought.
>>
>> http://www.tomschmitz.org/Contact%20PatchFrame1Source1.htm
>
>
> Nice piece of work. I think the results are a little bit off, but your
> basic experiment is neat.
>
> It seems to me that the act of mounting a bike would cause the wheel
> to roll fore and aft slightly as well as rocking from side to side.
> Any motion would cause the contact area measurement to be exaggerated.
> In addition, you may load the front tire more heavily than the nominal
> value momentarily during the mounting process.
I was as careful as I could be to not have any of these things happen.
Of course, this being a backyard experiment, I didn't have 100% control
over everything. That's why I want to repeat it with an apparatus.
>
>
> I'm not convinced that the contact patch is 2 x Load/Presure with a
> "light road tire." The stiffness of the casing may make the contact
> patch slightly greater than L/P (i.e. 5-10%), but I'd be very
> surprised to see a factor of two.
Well, the nice thing about conducting my own research is that it gives
me something to think about, learn about, and I always reserve the right
to be wrong.
> And by the way, the ideal gas law has nothin' to do with it. You could
> have an incompressible fluid in your tire and the balance of force
> would still predict the same contact area for a given pressure.
That is a tongue in cheek comment - I think I clearly stated that gas
laws have nothing to do with the experiment. Though I might rethink that
if more closely controlled experiments bear out the initial
results...... (that was a bit tongue in cheek, too)
Regards,
Tom
>
>