Newsgroups: rec.bicycles.tech
From: jbrandt@hpl.hp.com (Jobst Brandt)
Subject: Re: "Slicks" tyres advice needed
Date: Mon, 22 Jan 1996 00:30:39 GMT

Roger Marquis writes:

> There is really only one drawback to slick tires on pavement and that's
> wet traction.  Even fat slicks can be very slippery compared to treaded
> tires on wet roads.  Knobby tires on the other hand have little
> traction on wet _or_ dry pavement.

Unless the words "can be very slippery" are a dodge, this statement is
without foundation and reeks of bicycling myth and lore.  It took
decades for smooth tires to migrate from dragsters to racing cars, and
more decades after that to make the transition to motorcycles.  Today,
Bicycles are the last holdout even though theirs are the least water
affected tire of the vehicles mentioned.

For the bicycle, the width of the contact patch, its shape, and the
inflation pressure, combined with the bicycle's relatively low speed,
make water on the road no more a hazard than a light film of moisture.
All the water that can be made to escape from between tire and road,
does this better without tread features than with.  Water on slick
surfaces, such as paint stripes, manhole covers, or railway tracks
cannot be removed by tread patterns, just as a sharp edged squeegee
glides over a wet window.

The contact patch of a bicycle tire is a sharply pointed conoe-shape
that first makes contact in the center and spreads as the contact area
increases toward the center of pressure.  Similar to aircraft tires
that are also smooth except for tread depth gauging grooves, the round
cross section prevents water entrapment as that makes hydroplaning
possible with automobile tires with their rectangular contact patch
having a broad front.  Road bicycles need tread about as much as a
garden wheelbarrow.  Of course the wheelbarrow has tread for the same
spurious reasons.

It is evident that the tread on current motorcycles is essentially
smooth except for some widely spaced artistic lines.  The flat and
smooth areas between them are many times as large as bicycle tire
contact patches.  These tires are neither directional nor do they have
micro sipes or any "drainage" grooves.  When I read bicycle tire
advertisements today, they remind me of motorcycle tire ads from
magazines of 40 years ago.  I think that is the fare to which Roger is
treating us.

Jobst Brandt      <jbrandt@hpl.hp.com> 

Newsgroups: rec.bicycles.racing,rec.bicycles.tech
From: jbrandt@hpl.hp.com (Jobst Brandt)
Subject: Re: bicycle tire science (was "Re: drifting")
Date: Wed, 20 Mar 1996 01:03:03 GMT

Matt O'Toole writes:

>> This has been conclusively established on tire testing equipment
>> both at the joint tire testing facility in Japan (IRC) and on
>> equipment that I designed for Avocet to measure RR and breakout
>> lean angle of various tire designs.

> If such testing facilities actually exist, why do they keep selling
> tires that go against all common sense design principles?  Why does
> IRC keep selling road racing tires with tread, and mountain bike
> tires with squishy, useless knobs?

It is easier to pander to the fears of the customer than to try to
reverse commonly held beliefs.  Since cornering is not a primary demand
in racing, and most racers are not ones to press that facet of racing,
tires with fine profiles will continue to be the choice of riders.
Motorcycles, until recently, had deep tread patterns on road machines.
Today, from imitating racing tires, they generally ride slicks that
have enough tread lines in them to pass the law that states that motor
vehicles shall not operate with slick tires, a law based on automobile
tires that have a cylindrical surface instead of a toroid.

> Why does Avocet still make those stupid, heavy, slow inverted tread
> things?

They sell like hotcakes.  They exemplify my point that it is easier to
give the customer what he believes than to change the concept.

Jobst Brandt      <jbrandt@hpl.hp.com> 

From: jbrandt@hpl.hp.com (Jobst Brandt)
Newsgroups: rec.bicycles.misc
Subject: Re: slicks vs treads
Date: 14 May 1997 22:22:26 GMT

Craig Rusbult writes:

> I'm debating between slicks (Metro Kevlar, 26 x 1.50) and treads
> (Trek Invert-2, Kevlar, 26 x 1.50) and I'm wondering what people's
> experience is with the two types of tires.  (the Metro is slick in
> the middle, very shallow/narrow grooves along the sides; the
> Invert-2 has a continuous zig-zag center tread and fairly shallow
> grooves on the sides)

Here is a small piece on tire treads and their effects.  I have ridden
nothing but Slick or effectively slick tires since the days when only
tubulars were available in high pressure tires.  It was this
experience that brought out the Avocet FasGrip tire series of slicks
that I have used exclusively since their introduction.  I use them on
all terrain as do many other riders who use road bikes where others
believe only MTB's should travel.

-----------------------------------------------------------------------
Subject: 8.62  Rolling resistance of Tires
From: Jobst Brandt <jbrandt@hplabsz.hpl.hp.com>

The question often arises whether a small cross section tire has lower
rolling resistance than a larger one.  The answer, as often, is yes
and no, because unseen factors come into play.  Rolling resistance of
a tire arises almost entirely from flexural rubber losses in the tire
and tube.  Rubber, especially with carbon black, as is commonly used in
tires, is a high loss material.  On the other hand rubber without
carbon black although having lower losses, wears rapidly and has
miserable traction when wet.

Besides the tread, the tube of an inflated tire is so firmly pressed
against the casing that it, in effect, becomes an internal tread.
The tread and the tube together absorb the majority of the energy lost
in the rolling tire while the inter-cord binder (usually rubber) comes
in far behind.  Tread scuffing on the road is even less significant.

Patterned treads measurably increase rolling resistance over slicks,
because the rubber bulges and deforms into tread voids when pressed
against the road.  This effect, tread squirm, is mostly absent with
smooth tires because their tread cannot be deformed laterally by road
contact.  Rubber, although elastic, is incompressible.

Small cross section tires experience more deformation than a large
cross section tire and therefore, should have greater rolling
resistance, but they generally do not, because large and small cross
section tires are not identical in other respects.  Large tires nearly
always have thicker tread and often use heavier tubes, besides having
thicker casings.  For these reasons, smaller tire usually have lower
rolling resistance, rather than from the smaller contact patch to which
it is often attributed.

These comparative values were measured on various tires over a range
of inflation pressures that were used to determine the response to
inflation.  Cheap heavy tires gave the greatest improvement in rolling
resistance with increased pressure but were never as low as high
performance tires.  High performance tires with thin sidewalls and
high TPI (threads per inch) were low in rolling resistance and
improved little with increasing inflation pressure.

As was mentioned in another item, tubular tires, although having lower
tire losses, performed worse than equivalent clincher tires because
the tubular's rim glue absorbs a constant amount of energy regardless
of inflation pressure.  Only (hard) track glue absolves tubulars of
this deficit and should always be used in timed record events.

The contact patch of a slick bicycle tire is a long sharply pointed
canoe shape that displaces water better than any tread can.  The width
of this contact is smaller than the smooth area of most any car tire
and certainly smaller than the smooth tires of commercial aircraft
that have tread thickness indicating grooves about 4-6 inches apart.
They, having round cross section tires also displace water but at up
to 200mph, not 30-40mph as a bicycle.  Hydroplaning on a bicycle is
not a consideration the same as wheel balancing is not.  Neither
effect comes into play at the tire sizes and speeds that occur.

------------------------------

From: jbrandt@hpl.hp.com (Jobst Brandt)
Newsgroups: rec.bicycles.misc,rec.bicycles.tech
Subject: Re: slicks vs treads
Date: 15 May 1997 01:19:35 GMT

Ken Kifer writes:

> Someone else has objected to the word "hydroplaning"; let's just use
> slipping or sliding instead.  I only once noticed a problem with a
> slick tire.  I was on a smooth highway on a wet day, and I almost
> lost control from a fresh paint stripe.  Traction was zero for an
> instant.

As I have often pointed out.  There is no tire that will give traction
on a slick surface such as a paint stripe, manhole cover, railroad
track or any smooth homogeneous material with a water film on it.  It
takes micro grit to penetrate the lubricating water layer.

You can test this by running a squeegee over a wet car window on a
sunny day and see the difference between wet and the second swipe when
it is dry.  A rubber Squeegee has the sharpest rubber tread edge
available and it glides effortlessly over wet glass.  Boundary layers
are not easily removed and a tire tread does a lot worse job than a
squeegee.

If this example does not demonstrate how strong boundary layers are,
you might consider the razor blade that does not penetrate the
boundary layer of water on your skin when you shave.  If you dry your
skin with alcohol, allowing it to evaporate, a sharp blade will cut
the skin.  The argument that a slick tire caused a slip on a railroad
track is like saying the slick caused you to fall on ice.

Jobst Brandt      <jbrandt@hpl.hp.com>

From: jbrandt@hpl.hp.com (Jobst Brandt)
Newsgroups: rec.bicycles.misc,rec.bicycles.tech
Subject: Re: slicks vs treads
Date: 15 May 1997 18:17:58 GMT

Dr.(biophysics) David Martin writes:

> Do tyres grip as well in wet conditions?

Wait a minute.  You just told us that they hydroplane.  Now you ask
whether they grip in the wet.  The Dr. is [OUT].

> The incident I was referring to was on very smooth asphalt, almost
> as smooth as a paint strip. In most cases the asphalt provides
> enough pressure points (each stone) to allow a high pressure point
> from which the water will be dispelled. Now, you know as well as I
> do that for something to move there has to be a pressure gradient,
> and the larger the gradient the greater the force.

I don't recall "an incident" but rather that you flatly stated that
smooth tires hydroplane.  That traction is poorer on wet surfaces is
well known.  That new pavement has residual oil and that this reduces
traction, especially with water, is also known.  That tread patterns
improve this situation was your contention and I explained why that is
not the case, as long as hydroplaning is not occurring, because
boundary layer fluid is difficult to displace.

It is not each stone, but the fine structure of those bits of gravel
that cause traction.  Traction is affected by the dimensions in
micrometers, about at the limit of unmagnified visible observation.

>> How about not alluding to knowledge that you don't have.

> I don't believe I did. My research affiliation is shown clearly in my
> sig. I have never claimed to be an expert researcher in tyre mechanics,
> I was merely putting forward a lay explaination.

So why do you list it?  Your sig is at the bottom.  I hope you
introduce yourself at social gatherings as Dr.  That way in the event
of a medical emergency, you will be the first called.  I guess you
worked hard for that title.

>>> On loose surfaces the grip depends on the shear between the dirt
>>> and the underneath. That is why MTBs have big tractor like tread,
>>> to dig down into the dirt and push it with a big shear plane.
>>> Otherwise you end up using the top surface layer as a row of tiny
>>> ball bearings and just spin.

>> If the tire does not make an impression on the soil, the tread does
>> not improve traction as you claim.

> Indeed. that is why tread has no effect on immovable substrates, and
> why  slicks are faster on solid surfaces.

Oops, how did "substrates" slip in here.  I see you are truly a
scientist who rides around on substrates.  Wow.

>> The knobs can reach hardpack between the 'marbles', but this is
>> only under ideal conditions.  The main effect is that a larger low
>> pressure tire gets a broader average of the loose surface.

> But that would mean that slicks and treaded tyres of the same
> dimensions have the same grip. Which is not true.

That is an unwarranted deduction.  The point is that knobs don't give
the traction advantage that is often attributed to them mainly because
they are wasted on a hard surfaces.

>>> Try taking an MTB fitted with a treaded tyre and a then with
>>> slicks through a hard corner on tarmac. You'll soon notice the
>>> difference.

>> Yes, the knobby washes out at about half the lateral thrust.  But
>> then we weren't talking about knobby tires, but rather smooth or
>> treaded road tires that have pseudo automotive tread.

> Depends what you consider an 'automotive tread'. Here we have a lot
> of M+S rated tyres. they look more like MTB tyres.

The point is that you changed the subject.  We were talking about
tread having a positive effect on wet pavement, not whether knobs work
in the dirt.

> These treads may conceivably make a difference in some extremely rare
> circumstances, but are probably there for marketing purposes (or as a
> handy depth guage to let you know when the tyre is worn out).

Thanks.  I think we're back where we started.  In fact I am sure I
said that in this thread.  How perceptive of you to notice.

>>> Its also strange how race cars use slicks in almost every race
>>> except when they need to worry about aquaplaning.

>> To you it may be strange, but to those who understand that even
>> rain tires in F1 have slick tread areas larger than those of a
>> bicycle, yet they travel at substantially greater speed and with
>> lower tire pressure.

> I'll have to try to write in American instead of English. In the wet
> in F1 hydroplaning is a given. That is what the above statement
> alluded to though in a typically British manner. The principal is
> established that hydroplaning can occur.

That has not been established and if the UK uses a different
definition of aquaplaning/hydroplaning then you'll have to supply
that.  Here and on the continent it is separation of tire and road by
liquid water in contrast to boundary layer wetness of the contacting
surfaces.  Those who have experienced it know that the steering of a
car turns freely and without effect when hydroplaning.

> A quick definition that you may care to dispute: 'Hydroplaning
> occurs when the speed of removal of water from between the tyre and
> the road is insufficient to allow the tyre to contact the road.'

You'll have to do better than that because contact is also lacking in
precise meaning here.  As I said, the result is flotation and that
fits your definition as well.

> In the wet in bike racing hydroplaning is rare (not non existent).

You can ride through water deeper than the depth of tire and rim and
not get hydroplaning at speeds up to 40 mph on a bicycle.  I have
ridden through such water without falling and had good steering
control.  A two wheeled vehicle cannot be ridden any distance while
hydroplaning because it offers less traction than smooth ice at the
melting point.

> If you put two smooth surfaces together (ie a paint stripe and a
> slick tyre) with a layer of water between them, you will get
> hydroplaning under certain conditions (relatively high speed).

That is not hydroplaning.  That is boundary layer lubrication.  As
I pointed out, smooth homogeneous surfaces have no fine structure
that can break through the boundary layer as does the fine grit of
conglomerate paving rock or the sharp facets of crystalline rock
surfaces.

> Having a tread makes the interface less smooth, giving points of
> higher pressure, giving a pressure gradient, giving exclusion of
> water from the interface so increases the amount of rubber on the
> road at that point.

I guess you missed the item about a squeegee and that its edge is
the sharpest rubber edge offered commercially.  It glides over water
on glass effortlessly.  If you think you know of a tire tread that can
do better than that, please don't keep it a secret.

> Of course this only really matters if you are running slicks on a
> slick surface. I happened to find one such surface (on which braking
> in the dry is very good on the same tyres) in the rain and the water
> removal at the speed I was going (which was too fast for the
> conditions) was insufficient. I have never experienced it on tarmac
> since, just on paint stripes and manhole covers or similar features.

Yes?  And have you compared your slicks with other tires on these same
surfaces?  I doubt you will find any difference.  In fact a good way
to fall on you ass on a wet surface is to put the rear edge of a
rubber heel on it.  The flat surface of a rubber sole usually has
enough grit on it to prevent sliding.  Vibram soles contain plenty of
carbon black for that purpose.

Jobst Brandt      <jbrandt@hpl.hp.com>

From: jbrandt@hpl.hp.com (Jobst Brandt)
Newsgroups: rec.bicycles.misc
Subject: Re: slicks vs treads
Date: 16 May 1997 01:31:14 GMT

Frank Miles writes:

> I'm not interested in getting tangled in this melee, as fun as it
> might seem.  I'd like to ask a question, in parts based on an
> earlier assertion-- that there was no real cost differential
> involved in producing slick vs. treaded tires.

The difference lies in the casings on which the treads are molded.
High performance tires are either slick or nearly so.  That is given
by the thin tread rubber they must have to keep rolling resistance at
an acceptable level.

> Q: If the treaded tires are 'lower grade' (and thus presumably lower
> cost), where is the extra money going?  Could some of the
> performance differences arise from other materials or assembly
> costs?  Any way to assess how much?

Patterned tread has a more expensive mold and come out of that mold
somewhat more slowly than the slicks.  The cost per tire for the mold
is insignificant.  The handling cost is also "in the noise" as they
say with measurements with practically no variation.

Jobst Brandt      <jbrandt@hpl.hp.com>

From: jbrandt@hpl.hp.com (Jobst Brandt)
Newsgroups: rec.bicycles.tech
Subject: Re: slicks vs treads
Date: 21 May 1997 00:18:01 GMT

Tom Holland63 writes:

> Traction aside, I find the real advantage to slicks in the wet is
> that they pick up and throw less water and grit.  Ride behind one
> and you'll be thankful for the smaller rooster tail.

I think that was the first thing I noticed, years ago, when I switched
from a clunk with mini-automobile tread to a good bike with tubulars.
I no longer got water in the face from an uncovered front tire, and a
lot less spray up my back.  I still often hear from people with
conventional tread complain of water in the face from their own bike
without mudgaurds.

Jobst Brandt      <jbrandt@hpl.hp.com>

From: jbrandt@hpl.hp.com (Jobst Brandt)
Newsgroups: rec.bicycles.tech
Subject: Re: wet weather clinchers
Date: 3 Mar 1999 02:12:41 GMT

Doug Berlin writes:

> Treaded tires give better traction on wet road surfaces.

Is this a commandment handed down by the tire gods or just an urban
legend?  Please explain why your contention should be believable.

Jobst Brandt      <jbrandt@hpl.hp.com>
----------------------------------------------------------------------
From the FAQ:

Subject: 8.70  Tires with smooth tread
From: Jobst Brandt <jbrandt@hplabsz.hpl.hp.com>
Date: Fri, 05 Dec 1997 16:29:59 PST

Drag racers first recognized the traction benefits of slick tires,
whose benefit they could readily verify by elapsed times for the
standing start quarter mile.  In spite of compelling evidence of
improved traction, more than twenty years passed before slicks were
commonly used for racing cars, and another twenty before they reached
racing motorcycles.  Today, slicks are used in all weather by most
street motorcycles.  In spite of this, here at the end of the
millennium, 100 years after John Dunlop invented the pneumatic tire
for his own bicycle, bicyclists have not yet accepted smooth tread.

Commercial aircraft, and especially motorcycles, demonstrate that a
round cross section tire, like the bicycle tire, has an ideal shape to
prevent hydroplaning.  The contact patch, a pointed canoe shape,
displaces water exceptionally well.  In spite of this, hydroplaning
seems to be a primary concern for riders who are afraid to use smooth
tires.  After assurances from motorcycle and aircraft examples,
slipperiness on wet pavement appears as the next hurdle.

Benefits of smooth tread are not easily demonstrated because most
bicycle riders seldom ride near the limit of traction in either curves
or braking.  There is no simple measure of elapsed time or lean angle
that clearly demonstrates any advantage, partly because skill among
riders varies greatly.  However, machines that measure traction show
that smooth tires corner better on both wet and dry pavement.  In such
tests, other things being equal, smooth tires achieve greater lean
angles while having lower rolling resistance.

Tread patterns have no effect on surfaces in which they leave no
impression.  That is to say, if the road is harder than the tire, a
tread pattern does not improve traction.  That smooth tires have
better dry traction is probably accepted by most bicyclists, but wet
pavement still appears to raise doubts even though motorcycles have
shown that tread patterns do not improve wet traction.

A window-cleaning squeegee demonstrates this effect well.  Even with a
new sharp edge, it glides effortlessly over wet glass leaving a
microscopic layer of water behind to evaporate.  On a second swipe,
the squeegee sticks to the dry glass.  This example should make
apparent that the lubricating water layer cannot be removed by tire
tread, and that only the micro-grit of the road surface can penetrate
this layer to give traction.  For this reason, metal plates, paint
stripes, and railway tracks are incorrigibly slippery.

Besides having better wet and dry traction, smooth tread also has
lower rolling resistance, because its rubber does not deform into
tread voids.  Rubber being essentially incompressible, deforms like a
water filled balloon, changing shape, but not volume.  For a tire with
tread voids, its rubber bulges under load and rebounds with less force
than the deforming force.  This internal damping causes the energy
losses of rolling resistance.  In contrast the smooth tread transmits
the load to the loss-free pneumatic compliance of the tire.

In curves, tread features squirm to allow walking and ultimately,
early breakout.  This is best demonstrated on knobby MTB tires, some
of which track so poorly that they are difficult to ride no-hands.

Although knobby wheelbarrow tires serve only to trap dirt, smooth
tires may yet be accepted there sooner than for bicycles.

------------------------------

From: jbrandt@hpl.hp.com (Jobst Brandt)
Newsgroups: rec.bicycles.tech
Subject: Re: wet weather clinchers
Date: 4 Mar 1999 17:53:25 GMT

Doug Berlin writes:

>> Is this a commandment handed down by the tire gods or just an urban
>> legend?  Please explain why your contention should be believable.

> It is neither a commandment, and it is obviously not extracted from
> the FAQ (aka The Book of Jobst)

> Rather, it is the result of applying logic and knowledge of
> engineering and physics to a practical problem.

More precisely a problem of tribology.

> It should be obvious that the ideal tread for a tire, in terms of
> traction, would have a profile that was the inverse of of the texture
> of the surface of the road that was being ridden on.  This being
> impossible, it would still be advantageous to have a tire that had
> tread features of comparable scale to the irregularities in the
> asphalt (or whatever) road surface.

I think you are confusing gears with sliding friction and stiction,
aka static friction that isn't sliding.  When a boundary layer of
liquid lies between tire and road, it is the microstructure of grit in
the road surface that makes contact between rubber and road.  Whether
you like the item in the FAQ or not, I think you could be more
constructive by refuting what it says rather than to say "it should be
obvious...".

> That way , at least some purchase could be obtained between the tire
> and the road when there was some lateral force due turning or
> cornering.

I don't know what you mean by "purchase" but the water film is a
lubricant and rubber features cannot penetrate it, only the fine
structure of pavement aggregate can do this.

> Also, I don't know where this "squeegeeing" business fits in.

It shows that even the sharpest tread features cannot penetrate the
boundary layer of water over which it glides.  Therefore, it is
pavement roughness that must reach the tire and the effective part of
that roughness is in the 0.001 inch range, not the macro size of tread
rubber features.

> I don't know what roads you're riding on in California, but the only
> ones I've ever seen have more than just a microlayer of grit
> penetrating a microscopic layer of water after a tire tread passes
> over them.

The moisture that makes pavement slippery doesn't need to come from
rain.  It can be furnished by fog such that there isn't even any spray
from the tires.  The water layer of interest is as thin as the
condensing moisture from your breath on a piece of glass.  The splash
you see is entirely above and beyond the amount of water required to
make pavement as slippery as water can make it.

> They're ROUGH SURFACES.  It's the irregularities of the road surface
> that a fine tread can gain traction with.  As far as squirming,
> maybe on a big knobby tire I see your argument, but on a finer tread
> with features of <=1mm?  Give me a break.  And who cares about the
> minor difference rolling resistance, it's sure not going to make me
> win any more races or ride THAT much faster.

Your friction model of interlocking blocks does not work.  An example
would be diamond pattern steel plate that is just as slippery as flat
steel when wet.

>> Not only did bicycle racers ride slicks in the rain but accurate
>> measurements were made on test machinery to show that patterned tread
>> reduced traction both on wet and dry surfaces.  Although you might
>> want to relegate it to advertising, Avocet did extensive tests on the
>> road, wet and dry, and published the photos of riders at the same
>> steep lean angles achieved on the machine.

> Yes, I would like to relegate it to advertising.  It was done by
> Avocet.  Not exactly objective.

You mean by that the photographs of the riders who were leaning at
steeper angles than one can achieve with patterned tread were biased
by the photographer?  You may disagree with the text that accompanied
the pictures but I don't see how the angle between rider and road is
not objective.  Can you explain what you mean.

Jobst Brandt      <jbrandt@hpl.hp.com>

From: jbrandt@hpl.hp.com (Jobst Brandt)
Newsgroups: rec.bicycles.tech
Subject: Re: wet weather clinchers
Date: 4 Mar 1999 21:15:44 GMT

Joey D'Antoni writes:

> I have a question for you.  Is there any significant effect of
> lowering tire pressure (to increase rolling resistance and therefore
> traction) in the rain?  It is legend that was handed down, and I was
> just wondering if there was any basis in science for it.

I don't know.  I haven't had the opportunity to run slip-out tests on
the Avocet tire testing machine since the original ones some years
ago.  I suspect lower pressure with a larger contact patch would
benefit traction because it would give a larger average of slick and
non slick spots.  In that respect, I am reminded of a smooth rubber
heel, on a mans dress shoe, that slips on wet surfaces far more easily
on the trailing edge when tilted up than on its surface.

If I have a chance to make such a test, I certainly will and I would
report the results.

Jobst Brandt      <jbrandt@hpl.hp.com>

From: jbrandt@hpl.hp.com (Jobst Brandt)
Newsgroups: rec.bicycles.tech
Subject: Re: wet weather clinchers
Date: 6 Mar 1999 01:59:54 GMT

Doug Berlin writes:

>>> Rather, it is the result of applying logic and knowledge of
>>> engineering and physics to a practical problem.

>> More precisely a problem of tribology.

> My argument isn't exactly one of triblolgy.

>> I think you are confusing gears with sliding friction and stiction,
>> aka static friction that isn't sliding.  When a boundary layer of
>> liquid lies between tire and road, it is the microstructure of grit
>> in the road surface that makes contact between rubber and road.
>> Whether you like the item in the FAQ or not, I think you could be
>> more constructive by refuting what it says rather than to say "it
>> should be obvious...".

> OK ...I'm not confusing anything, and my argument doesn't have to do
> with friction so much as the interaction between a treaded tire and
> the macroscopic irregularities of the road.

> The textbook explanation of static friction generally refers to two
> macroscopically smooth surfaces in contact with one another, and the
> static friction arises from the microscopic irregularities (such as
> the microstructure of grit you mention) of the two surfaces
> "catching" on one another.  If I were choosing a tire to ride on a
> wet, smooth surface like plastic or something equally smooth, I
> would agree that a slick would be the way to go.

Text books are often not good at characterizing friction and the one
you have is one of those.  Friction is not made of mechanical
interlocking, microscopic or otherwise.  That is why I dragged
Tribology into the discussion because the interaction of two sliding
objects that are smooth boils down to the shear strength of the softer
material over the "true" area of contact, in comparison to the
apparent contact.  Since most materials are not sufficiently flat to
make molecular contact over large areas, they must be pressed together
by the oft mentioned normal force.  Up to the point of full contact, a
ratio exists between normal force and drag force, known as the
coefficient of friction.

Once a skid starts, rubber begins to melt on dry pavement and
increases its contact greatly, however, it also loses shear strength
so that for ordinary tires traction decreases once skidding that
leaves a black mark starts.  Drag racers have a large enough contact
patch to operate at an intermediate stage where the rubber begins to
melt and still has shear strength.  Exceeding this limit quickly leads
to smoke and a burn-out typical of a skidding tire.

The point is that none of this relies on mechanical interlocking of
particles, the tire being made of a homogeneous flexible medium that
can deform to match the road surface.  Therefore the roughness of the
road is not a benefit to traction but only for water dispersion and
break down of the lubricating boundary layer of water.  Just the same,
when the boundary layer is reduced to several molecular layers, it no
longer acts as a liquid because only in bulk do water molecules move
freely in response to pressure.  A water molecule between two solid
bodies is acts as glue because it firmly attaches to both and does not
easily allow motion.  How well water attaches to solids is evident in
vacuum chambers from which water must be driven by radiant energy or
heat.

> But, roads have macroscopic irregularities, usually pits or whatever
> you want to call them , whatever you want to call them, and by
> choosing a tire with tread features (of an inverse or male shape)
> that are of similar (or somewhat smaller) scale than these pits, one
> can obtain resistance to slipping in turns due to the "mating" of
> these features.

This is not a realistic model of friction between rubber tire and road
as I have tried to make clear.  I think you'll find that a rubber tire
has better traction on a plate of glass than on the road.  This can be
demonstrated with a constant normal force by pulling the tire over a
horizontal surface under constant load.  Using a tilting device does
not show the same thing because at the break loose point insufficient
normal force remains to give any difference in contact area.  Besides,
that would be a stiction test rather than a traction test.

>> I don't know what you mean by "purchase" but the water film is a
>> lubricant and rubber features cannot penetrate it, only the fine
>> structure of pavement aggregate can do this.

> The rubber doesn't have to penetrate it.  In the case where a tread
> is in a void or pit, it is the "wall" of the tread pushing against
> the "wall" of the pit.  The water film is being compressed between
> the two (approximately).

>> Therefore, it is pavement roughness that must reach the tire and
>> the effective part of that roughness is in the 0.001 inch range,
>> not the macro size of tread rubber features.

> Why is that?

By adding the lubricant you complicate the issue of friction, and as I
said, it takes micro features to penetrate the boundary layer that
causes smooth surfaces to be slippery.  It is not mechanical
interaction that is needed but rather intimate rubber to road contact
at pavement asperities to generate enough energy from micro-slip,
locally, to displace water and achieve true contact between road and
tire.  If the slip rate is high enough, water resupply is generated to
keep the asperities lubricated which is why once sliding on wet
pavement, traction decreases sharply.

>> Your friction model of interlocking blocks does not work.  An example
>> would be diamond pattern steel plate that is just as slippery as flat
>> steel when wet.

> No, that wouldn't be a particularly good example, since steel is
> obviously a completely different surface

What do you mean by different.  Steel gives good traction when dry.
What makes it poor is that its microstructure is on the molecular
scale and gives a smoothness without asperities to break the water
film.

>>>> Not only did bicycle racers ride slicks in the rain but accurate
>>>> measurements were made on test machinery to show that patterned
>>>> tread reduced traction both on wet and dry surfaces.  Although
>>>> you might want to relegate it to advertising, Avocet did
>>>> extensive tests on the road, wet and dry, and published the
>>>> photos of riders at the same steep lean angles achieved on the
>>>> machine.

> I would still relegate this to advertising.

>> You mean by that the photographs of the riders who were leaning at
>> steeper angles than one can achieve with patterned tread were
>> biased by the photographer?  You may disagree with the text that
>> accompanied the pictures but I don't see how the angle between
>> rider and road is not objective.  Can you explain what you mean.

> Yes.  The angle between the rider and the road is certainly objective
> to the extent that accurate measurements can be taken from different
> photographs (I question that from my own scientific experience).  And
> in each photo on different tires, where all other conditions identical
> (i.e. velocity, turning radius, rider position...)?

The comparisons were made on a machine.  Dave McLaughlin rode only on
Slicks in the road trials.  He was not willing to take a fall in order
to prove that other tires are worse.  That was measured on the
machine.  The photos were for the public's interest because lean angle
cannot be faked whereas one might argue what the machine was doing.

> And why this reference to lean angle (singular).  Clearly different
> roads will give you different levels of traction.  A brand new asphalt
> surface, nicely done, is really smooth. An old asphalt road will be
> much rougher.

So?  I wouldn't try cornering on wet shiny road striping or AT&T
manhole covers.  Are you saying that there is a cross-over point where
slicks, that are otherwise good on wet roads, become worse than
patterned tread on certain wet roads.  If that is your contention then
I think you should review the nature of sliding as has been expanded
on above.  Tread patterns have nothing to do with traction on hard
surfaces for skinny bicycle tires where macro-drainage is not an
issue.  All grooves do is reduce contact area, increase tread squirm
(RR) and give a mental crutch to those afraid of wet roads.

> Jobst, I definitely agree that in dry conditions, (and in all
> conditions on extremely smooth surfaces), slicks are superior.  I
> just argue that a lightly treaded (not knobby) tire will corner
> better in wet conditions.  You don't have to be an great athlete to
> test the cornering ability of a tire in the rain unsuccessfully.
> I've done it myself on a pair of Michelin Hi-lite Supercomps in a
> sudden thunderstorm.  Just ask a real cyclist like Matt Eaton (Milk
> Race winner 1983, Tour of Summerville winner) about riding slicks
> like that in the rain and he'll tell you before even you would have
> a chance to let him know your opinion.  Use a treaded tire.

That is your prerogative.  The difference is measurable but a slick
tire will not make wet roads dry.  I also believe that with about the
same rubber mixture, a fine texture (diamond ripple) has practically
no deleterious effect.  Considering that today many people ride
colored tires that have substantially poorer wet traction, shows that
they seldom ride near the limit of traction of even these tires.  They
are the hottest selling item in spite of their poor traction, high
price, and short wear life.  That is how important performance is in
the bicycle business and that is why bicycles will probably change to
slicks after wheelbarrows do, if ever.

Jobst Brandt      <jbrandt@hpl.hp.com>

From: jbrandt@hpl.hp.com (Jobst Brandt)
Newsgroups: rec.bicycles.tech
Subject: Re: wet weather clinchers
Date: 9 Mar 1999 01:28:39 GMT

Doug Berlin writes:

> Yes, but as a consumer and having no other interest in the outcome
> of this argument other than my belief in my own ideas, I'm skeptical
> when a guy from Avocet runs exepriments to determine the best tires
> and the best tires turn out to be Avocets.  Where is this test
> published, anyway?

Avocet did not come out better, there were others as good who also
used smooth tread.  Besides, Avocet tires are made by IRC and at the
time, IRC had introduced a new compound that had better traction and
about twice the wear life of the most popular tire of that time.  I
suspect that most other tires, not made by Michelin or Continental,
use the same tread compound today.

Jobst Brandt      <jbrandt@hpl.hp.com>

From: jbrandt@hpl.hp.com (Jobst Brandt)
Newsgroups: rec.bicycles.tech
Subject: Re: wet weather clinchers
Date: 9 Mar 1999 00:33:00 GMT

Doug Berlin writes:

[on why tread patterns on road tires are better for wet traction]

> Nothing more than the empirical experience of the majority of
> pro-riders and the majority of experienced cyclists I've ever spoken
> to on the issue, and myself.  I will grant you, however, that none of
> them ever rode on a wet asphalt-coated drum roller (to my knowledge),
> so their opinions about tire performance on such a surface is not
> known to me.

Test machinery to examine performance clouded by otherwise
uncontrolled influences is often simplified to treadmill methods.  How
would you propose measuring the slip-out angle of a tire at speed?
Whether this is the exact same value one might arrive upon on some
selected piece of road is irrelevant because even roads vary widely
enough to give different results.  These are comparative values after
all, not absolutes.  Besides, I don't know of any riders who would
volunteer for such duty, nor do I readily know of a means for measuring
this angle of a moving bicycle, at least not to the comparative
precision of interest.

Initially, I volunteered to do these tests on a 16ft long tilt bed
with asphalt pavement surface.  These rides were done a low speed,
increasing the tilt until the bicycle slid off the tilted roadway.
Because I could influence the result by the way I entered the tilted
section and how I exited, the drum tester was built.  I wore working
gloves and boots and put a few scrapes on them as well as on my leg.

> But since Jobst and some folk on R.B.T. disagree with them, they
> must all be wrong.  Or else it's just psychological, but that means
> they're still wrong.

I believe that most riders and most tire engineers agree with my
assessment of tread patterns and wet traction.  Plenty of evidence to
support my perception of the matter exists among bicyclists, tire
manufacturers and tribologists.

Jobst Brandt      <jbrandt@hpl.hp.com>

From: jbrandt@hpl.hp.com (Jobst Brandt)
Newsgroups: rec.bicycles.tech
Subject: Re: wet weather clinchers
Date: 9 Mar 1999 18:42:47 GMT

Doug Berlin writes:

>> Text books are often not good at characterizing friction and the
>> one you have is one of those.  Friction is not made of mechanical
>> interlocking, microscopic or otherwise.  That is why I dragged
>> Tribology into the discussion because the interaction of two
>> sliding objects that are smooth boils down to the shear strength of
>> the softer material over the "true" area of contact, in comparison
>> to the apparent contact.  Since most materials are not sufficiently
>> flat to make molecular contact over large areas, they must be
>> pressed together by the oft mentioned normal force.  Up to the
>> point of full contact, a ratio exists between normal force and drag
>> force, known as the coefficient of friction.

> Jobst, what you have done here is state categorically that my
> contention regarding friction is wrong, but you have -not- given is
> an explanation of what force discourages two surfaces in contact
> from slipping in the first place.  You mention shear strength, but
> that isn't it.  If the force isn't mechanical, then what is it?

The interaction involves van der Waals intermolecular forces that
explain how materials in intimate contact are held together.  This
effect becomes apparent with optically smooth surfaces that are
brought in contact with one another and are subsequently inseparable
without destructive means.  The sliders on the disk drive storing this
message are so smooth that were they to come to rest on the data
surface, they could not be moved without ripping the magnetic layers
from the disk.  Flexible materials are more easily separated because
they are peeled apart such that molecules are separated in small
numbers at a time.

>> Once a skid starts, rubber begins to melt on dry pavement and
>> increases its contact greatly, however, it also loses shear
>> strength so that for ordinary tires traction decreases once
>> skidding that leaves a black mark starts.  Drag racers have a large
>> enough contact patch to operate at an intermediate stage where the
>> rubber begins to melt and still has shear strength.  Exceeding this
>> limit quickly leads to smoke and a burn-out typical of a skidding
>> tire.

>> The point is that none of this relies on mechanical interlocking of
>> particles, the tire being made of a homogeneous flexible medium that
>> can deform to match the road surface. Therefore the roughness of the
>> road is not a benefit to traction but only for water dispersion and
>> break down of the lubricating boundary layer of water.

> Again, you dismiss but don't explain why mechanical interlocking isn't
> at all relied upon.  Then what is?

Mechanical interlocking plays a role but not as you propose.  Because
rubber is highly elastic and behaves as an incompressible liquid gel,
its shape is immaterial to sliding over a rough surface as is
demonstrated on an ice glazed chip-seal asphalt road.  The tire slides
over the road texture with its surface conforming to the roughness of
the road.  Shape of the rubber having no effect on traction.  Snow in
contrast has some shear strength and can be impressed with the shape
of the tire tread as is shown by the snow that a slipping drive wheel
throws.

>> Just the same, when the boundary layer is reduced to several
>> molecular layers, it no longer acts as a liquid because only in
>> bulk do water molecules move freely in response to pressure.  A
>> water molecule between two solid bodies is acts as glue because it
>> firmly attaches to both and does not easily allow motion.  How well
>> water attaches to solids is evident in vacuum chambers from which
>> water must be driven by radiant energy or heat.

> I can only figure this was included for the purposes of wowing you're
> minions or intimidating disagreers from vocalizing their disagreement,
> since it isn't directly relevant to disproving anything I've said.

It was a response to your question.  Don't be so cynical.

>> This is not a realistic model of friction between rubber tire and
>> road as I have tried to make clear.

> And you haven't succeeded.  I contend that rather than try to make
> clear you are trying to confuse the issue and intimidate me with
> barrage of indirectly related material.

Whether I succeed or not lies partly on your side to make an effort
to reconcile your views with those of scientific understanding of the
matter.  You must have a library at your disposal, where you can verify
what I write here.  It is not entirely an act of faith as you suggest.

>> I think you'll find that a rubber tire has better traction on a
>> plate of glass than on the road.

> Really?

Yes, really.

>> This can be demonstrated with a constant normal force by pulling
>> the tire over a horizontal surface under constant load.  Using a
>> tilting device does not show the same thing because at the break
>> loose point insufficient normal force remains to give any
>> difference in contact area.  Besides, that would be a stiction test
>> rather than a traction test.

> What the heck are you talking about?  Somehow you've gone from
> traction on asphalt to proving better traction on glass.  Next time
> I'm riding entering a  criterium to be held on a windshield, I'll test
> some tires in this manner ahead of time.

The point is that it is not mechanical interlocking of rubber tread in
pavement irregularities but contact between the two materials that
gives traction.  The reason I mention glass is that it is one of the
smoothest materials we regularly experience.

>>>> Therefore, it is pavement roughness that must reach the tire and
>>>> the effective part of that roughness is in the 0.001 inch range,
>>>> not the macro size of tread rubber features.

>>> Why is that?

>> By adding the lubricant you complicate the issue of friction, and
>> as I said, it takes micro features to penetrate the boundary layer
>> that causes smooth surfaces to be slippery.  It is not mechanical
>> interaction that is needed but rather intimate rubber to road
>> contact at pavement asperities to generate enough energy from
>> micro-slip, locally, to displace water and achieve true contact
>> between road and tire.

> Which -isn't- mechanical?

It is not mechanically interlocking as you propose.  You might think
about how sticky tape adheres to glass for example.  These are van
der Waals forces exemplified.

>> If the slip rate is high enough, water resupply is generated to
>> keep the asperities lubricated which is why once sliding on wet
>> pavement, traction decreases sharply.

> What is your point?  I'll see your asperities and raise you and
> obfuscation.

With velocity, a thicker lubricant layer is generated that exceeds the
height of asperities to penetrate.  This is a reason why a car that
loses traction can slide off the road once the wheels break loose,
even though during the slide the car slows to half its tracking speed.

>> What do you mean by different.  Steel gives good traction when dry.
>> What makes it poor is that its microstructure is on the molecular
>> scale and gives a smoothness without asperities to break the water
>> film.

> And....therefore it is -different-.  Different: adj. distinct or
> separate.  and if this is true, why would glass have such good
> traction when wet?

STOP already!  No one ever said glass has good wet traction.  It has
good dry traction as does steel.  Please take the effort to read what
you respond to so that it makes some sense.

>>> Yes.  The angle between the rider and the road is certainly
>>> objective to the extent that accurate measurements can be taken
>>> from different photographs (I question that from my own scientific
>>> experience).  And in each photo on different tires, where all
>>> other conditions identical (i.e. velocity, turning radius, rider
>>> position...)?

>> The comparisons were made on a machine.  Dave McLaughlin rode only on
>> Slicks in the road trials.  He was not willing to take a fall in order
>> to prove that other tires are worse.  That was measured on the
>> machine.  The photos were for the public's interest because lean angle
>> cannot be faked whereas one might argue what the machine was doing.

> So you mean treaded tires werem't used in the road trials?  Thats as
> good an argument as I can come up with to further question the
> tests.  Let me make sure I understand: Avocet sponsored tests, tests
> showed Avocet tires are best...give me a break.  BTW, in what
> peer-reviewed journals were these tests published?

These were not "road trials" but rather demonstrations that slick tires
work on wet roads.  None of the riders fell in these demonstrations
because none tested the limits of traction.  The relative slip-out
angles were determined by the machine that would spill no blood over
the issue.

>>> And why this reference to lean angle (singular).  Clearly
>>> different roads will give you different levels of traction.  A
>>> brand new asphalt surface, nicely done, is really smooth. An old
>>> asphalt road will be much rougher.

>> So?  I wouldn't try cornering on wet shiny road striping or AT&T
>> manhole covers.  Are you saying that there is a cross-over point
>> where slicks, that are otherwise good on wet roads, become worse
>> than patterned tread on certain wet roads.  If that is your
>> contention then I think you should review the nature of sliding as
>> has been expanded on above.  Tread patterns have nothing to do with
>> traction on hard surfaces for skinny bicycle tires where
>> macro-drainage is not an issue.  All grooves do is reduce contact
>> area, increase tread squirm (RR) and give a mental crutch to those
>> afraid of wet roads.

> Now how can you say that for sure when you also say (and I agree)
> that rubber is a flexible homogeneous medium taht deforms to road
> surfaces.  With a treaded tire, one would have more surface are to
> conform and make contact with the road.

If the tread pattern of an ink pad wetted tire is visible on a smooth
surface then it isn't making full contact.  If the voids in the tread
are not making contact the tread can deform (yield) under slip forces
and allow movement on the road even without slipping, however, other
parts of the tread that are not near a void will slip.  Tread squirm
under load also causes scrubbing and internal hysteresis losses in the
rubber, the major component of rolling resistance.

>> That is your prerogative.  The difference is measurable but a slick
>> tire will not make wet roads dry.  I also believe that with about the
>> same rubber mixture, a fine texture (diamond ripple) has practically
>> no deleterious effect.  Considering that today many people ride
>> colored tires that have substantially poorer wet traction, shows that
>> they seldom ride near the limit of traction of even these tires.
> How do you know they have poorer wet traction?  Have you ridden or
> tested them?  And how did the issue of colored tires suddenly come up?

It has always been there in the tire business.  In the days of yore,
tubular makers had TT tires that were not black and because they had
no carbon black, they had lower RR, but at the same time had poor wet
traction.  Most riders who used them ended up riding them in the wet
at some time and either slipped or fell due top their poor traction.

>> They are the hottest selling item in spite of their poor traction,
>> high price, and short wear life.

> and you know this is true because....

The tire industry has publications and the STLE tribology journal
report on the progress of getting away from carbon black.  These
compounds are being developed for the mini-cars like the Smart and
others to match the tires with the car paint.  The bicycle tire people
are jumping the gun on this by offering them as fashion and anything
else that will move tires.  The car people have not yet gotten the
required performance in either durability or wet traction they need.

>> That is how important performance is in the bicycle business and
>> that is why bicycles will probably change to slicks after
>> wheelbarrows do, if ever.

> You sure seem stuck on wheelbarrow wheels.  Why not try testing their
> traction on your wet asphalt-coated drum machine?   Or better yet,
> take some photos of you and Dave McLaughlin on a test track pushing
> wheelbarrows w/ treaded vs. slick tires...you could test their
> traction at various dumping angles.

I don't understand why you persist in your rude implications and wise
rejoinders.  You don't seem to wish to discuss the merits of the
subject but rather argue by innuendo.

> Jobst, just address my points succinctly and directly, don't try to
> dazzle me with your knowledge or technospeak.

I thought you said you were and engineer or at least an engineering
student who would understand the concepts involved, given the
opportunity.  I don't think this can be presented more simply than
what I have responded here.

Jobst Brandt      <jbrandt@hpl.hp.com>

From: jbrandt@hpl.hp.com (Jobst Brandt)
Newsgroups: rec.bicycles.tech
Subject: Re: Avocet Tires  was: Velocity Rims-Nipple Problems?
Date: 4 Apr 2000 00:45:16 GMT

Peter Armitage writes:

>> I see you believe everything.  It isn't true.  Fortunately I have
>> something to say about IRC smooth black tread (Avocet) tires and that
>> is why we still have them, in my estimation the best performing tire I
>> have used.  I've used a lot of different tires over the years.  If you
>> think you can influence Continental, your fooling yourself.

> How familiar are you with the differences in
> construction/composition between the slick Avocets and the old slick
> Michelin?  I'm not refering to the new floophy
> red/blue/green/whatever ones, but what is now refered to as the
> Michelin Classic and (I believe) used to be the Michelin Comp.

The Michelin tires used a different casing that is still a mystery to
me because it didn't seem to have a bias ply.  The part that I didn't
like about them is that the rubber cracked in a short time.  It was
only the existence of these tires that I could convince Avocet to make
smooth tires.  IRC thought we were crazy.

Jobst Brandt      <jbrandt@hpl.hp.com>

From: jbrandt@hpl.hp.com (Jobst Brandt)
Newsgroups: rec.bicycles.tech
Subject: Re: Avocet Fasgrip (28 Road) where?
Date: 3 Sep 2000 00:28:07 GMT

Mark McMaster writes:

> Hey, what's with the patterned tread on the MultiGrip Avocet tires?
> These seem to be marketed as road models, where (as it has been
> pointed out in this newsgroup) patterned treads serve no purpose.

So I asked Avocet and they report that this is one of their best
selling tires and outsells its smooth counterparts by a wide margin.
I guess I can't fault them for pandering to the people who are afraid
of falling off their bicycles with slicks.  They probably never notice
that their tires are as slick as the FasGrips in a couple of days in
the hills.  Besides, the same people who argues here on wreck.bike
that slicks are dangerous in the wet are riding colored slicks today
with nary a worry.  Hey!  I saw them in the TdF, they must be better.

Jobst Brandt      <jbrandt@hpl.hp.com>

From: jbrandt@hpl.hp.com (Jobst Brandt)
Newsgroups: rec.bicycles.tech
Subject: Re: Tire threads and slush
Date: 8 Jan 2001 18:04:20 GMT

anonymous writes:

> I've often been told that tire thread has little value when cycling
> on the road. Mr. Brandt has often said that tire thread is mostly
> decorative. I'm wondering if people can comment on my experience.

No that's not what I said.  I said unless you make an impression on
the ground, TREAD has no effect.  I don't think that applies to
riding in snow, slush or otherwise.

> Last Friday, I was commuting home with a friend in about 2 inches of
> slush. The temperature was just below freezing and there were thin
> layers of ice forming.

> My bike has 1.75 inch slicks on it.  The friends bike has 2 inch
> nubby mountian tires.  My tires were at 50 lbs, my friend's around
> 40 lbs.  The bikes are otherwise almost identical and we are very
> close in weight.  As we were starting out, my rear wheel slid out
> from under me and I went down.  On the way home, I felt the wheel
> start to slide several times, but was able to put a foot down to
> keep from falling.  My friend said he had no trouble whatsoever in
> these conditions and rode much more aggressively than I could.

At least two things made a difference, his tread and lower inflation,
but then his riding skill may have also had an effect.

> So why did the nubbies help so much in the slush? Or is it the small
> differenceas in width and pressure?

Knobs on tires make dimples in snow that assist traction.  That's why
special knobbies are made for snow riding.  They have smaller knobs
because snow is an extremely fin grained substance.  Ice on the other
hand does better with slicks and carbide studs.

On the other hand, just slicks are better than profiles tread in pure
ice.  You won't make an impression on ice so you might as well
maximize contact area at the lowest pressure practical.  The trouble
is that most ice riding involves snow riding and knobbies are
essential for that.

Jobst Brandt      <jbrandt@hpl.hp.com>