Why bicycle tyres are different from car tires

On 25 Feb, 08:34, Ben C wrote:
But if all that's true, then why are treaded car tyres better? They
certainly aren't harder than the road either.

Treaded car tyres aren't necessarily better than slick; it depends on
the circumstances. For traction in dry conditions slick tyres are
best because they offer the maximum amount of rubber to grip the
tarmac. Think about Formula 1 racing, for example, where tyres in dry
conditions have no tread at all (except for the parallel grooves that
the rules require nowadays), unless they run in wet conditions in
which case slick tyres will aquaplane easily so they use treaded
tyres.

Bike tyres don't aquaplane - they are too narrow - so (for road use)
slick tyres are fine all the time.

Colin

On 2008-02-25, dabac wrote:
[...]
Ben C Wrote:
.. But if all that's true, then why are treaded car tyres better?
I believe it's mostly to do with hydroplaning. A car wheel travelling
through water quite easily generates a significant bow wave, and the
treads make it possible to drain some of that water rearwards instead of
having to push it all out of the way forwards.

And sidewards probably too.

That does make some sense-- the flat car tyre doesn't have the canoe
shaped contact patch, but a dirty great square one, so it needs the
treads to prevent aquaplaning.

But, clearly treads on car tyres do also improve braking and cornering
grip on wet roads (and not even necessarily soaking wet roads, just
quite wet ones, like after it's stopped raining).


Ben C Wrote:
..relatively un-worn treaded tyres grip much better for basic braking,
traction and cornering as any driver will know from practical
experience.

There are a bunch of unknowns in such a comparison, so I don't know how
useful it is.
But my personal theory is that the friction explanation
might be a bit simplified.

It's definitely simplified. Almost all friction explanations are.
"Friction" is a cover-all term for all kinds of subtle interactions that
make things grip together.

First you have friction as the "pure" surface phenomenon, but then you
also have friction as generated by a sheer mechanical interference fit
between two coarse surfaces - like dragging the business surface of a
waffle iron over another waffle iron.

Exactly, and I think that may happen to some degree with car tyres.

Ben C Wrote:
On 2008-02-25, dabac
wrote:
[...]
Ben C Wrote:
.. But if all that's true, then why are treaded car tyres better?
I believe it's mostly to do with hydroplaning. A car wheel
travelling
through water quite easily generates a significant bow wave, and the
treads make it possible to drain some of that water rearwards instead
of
having to push it all out of the way forwards.

And sidewards probably too.

That does make some sense-- the flat car tyre doesn't have the canoe
shaped contact patch, but a dirty great square one, so it needs the
treads to prevent aquaplaning.

But, clearly treads on car tyres do also improve braking and cornering
grip on wet roads (and not even necessarily soaking wet roads, just
quite wet ones, like after it's stopped raining).


Ben C Wrote:
..relatively un-worn treaded tyres grip much better for basic
braking,
traction and cornering as any driver will know from practical
experience.

There are a bunch of unknowns in such a comparison, so I don't know
how
useful it is.
But my personal theory is that the friction explanation
might be a bit simplified.

It's definitely simplified. Almost all friction explanations are.
"Friction" is a cover-all term for all kinds of subtle interactions
that
make things grip together.

First you have friction as the "pure" surface phenomenon, but then
you
also have friction as generated by a sheer mechanical interference
fit
between two coarse surfaces - like dragging the business surface of
a
waffle iron over another waffle iron.

Exactly, and I think that may happen to some degree with car tyres.

Some years ago the phrase "everybody" was using over here when
discussing tyres was "siping", something that was found primarily on the
tyres of heavier vehicles. Siping referred to making fine cross-hatched
cuts w/o removing any material across the tyre. The accompanying theory
then stated that when a force (cornering, accelerating, braking...) was
applied, all these densely packed blocks would cant a little, thus
exposing a lot of edge that was ready to bite into the surface to
provide traction.
It was, for a while, the favourite excuse as to why buses and trucks
shouldn't be required to use studded winter tyres when travelling on
icy/snowy roads.

Don't know it it's still around.


--
dabac

Ben C? writes:

1. Contrary to common opinion, for any given rubber compound, (on
bicycles) slick tyres are better in the wet than tyres with tread.

2. They also tend to roll slightly better.

3. Bicycle tyres with tread are only beneficial on soft surfaces,
not on tarmac.

This has been gone over many, many times in this newsgroup. Rather
than rehash it yet again, try a Google search, or simply consult
the FAQ-

http://draco.acs.uci.edu/rbfaq/FAQ/8b.13.html

I have a few questions about that post.

It claims that slicks are used in all weather by most street
motorcycles. I'm fairly sure motorbikes for road use don't have
slick tyres and that it's dangerous and illegal to ride them around
with bald or slick tyres. If you watch the Moto GP on TV, as soon
it rains they all start falling off and dashing into the pits for
their "wets" (which have treads).

You should attend a motorcycle race and look at those tires. As most
road tires I see here, they are slicks with zigzag grooves from which
one can see how much rubber thickness is left. The slick areas
between these rubber depth grooves are each larger than the entire
contact surface of a bicycle tire. For rain racing, mainly the tread
compound is different but still essentially smooth. Some moto rain
tires have drainage groves because they travel about three times as
fast as bicycle speeds or more. That gives them a bit of mush for a
transition between tracking to sliding.

I believe bicycles don't aquaplane. Cars rarely aquaplane either,
but relatively un-worn treaded tyres grip much better for basic
braking, traction and cornering as any driver will know from
practical experience. So why is the same effect not possible on a
bicycle? I'm thinking in particular of 47mm road tyres at 60psi or
so, rather than 23mm at 110psi.

If landing commercial aircraft don't aquaplane then bicycles won't do
so. Cars have a straight flat contact front that lifts off at high
speed. It occurs easily with as little as 10mm water depth on a
fairly smooth road. If you doubt the hardness of water at such speed,
you should try 10m tower diving in a swimming pool and feel the
impact.

The article says, "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".
There follows a parable about window-cleaning squeegees to
demonstrate that it's impossible for a tread to push water out of
the way.

But if all that's true, then why are treaded car tyres better? They
certainly aren't harder than the road either.

To prevent aquaplaning and give traction on snow or mud.

The lubricity of water is much misunderstood. If you shave with a
blade, you have a sharp edge that glides over skin and leaves it wet.
Boundary layer lubrication is not obvious from casual observation but
in mono-molecular layers, liquids behave more like solids and do not
displace readily. See Van der Waals forces, the ones with which
Geckos climb walls.

It's claimed that "machines that measure traction show that smooth
tyres corner better on both wet and dry pavement". Does anyone know
any more about these tests, and what sort of tyres were tested?

They were performed on the Avocet tire tester that has a 6' diameter
asphalt paved drum on which a bicycle tire is loaded with a pneumatic
piston against the drum and tilted as in cornering. The washout angle
is recorded by the computer that controls the machine. The drum can
run dry or have a mist sprayed on its asphalt surface.

Jobst Brandt

On Sun, 24 Feb 2008 23:42:46 -0700, wrote:

On Sun, 24 Feb 2008 22:07:18 -0800 (PST), Hank
wrote:

1. *Contrary to common opinion, for any given rubber compound, (on
bicycles) slick tyres are better in the wet than tyres with tread.

2. They also tend to *roll slightly better.

3. Bicycle tyres with tread are only beneficial on soft surfaces, not
on tarmac.

#s 1 & 3 are obvious on their face.

In the case of 1, slick guarantees more contact with the road. Bike
tires are too narrow to hydroplane, so there's no need for channels to
evacuate water.

As for #3, on soft surfaces, the ground deforms in deference to the
tire. On hard surfaces, the tire must deform in deference to the road.
So a slick tire at pressure low enough to deform (which also increases
the contact patch area) but not bottom out provides the best traction.

I'll let someone else tackle #2, because I don't fully understand the
science of rolling resistance, and won't shame myself by, as the
Russians say, talking out my nose on the subject.

Dear Hank,

The usual explanation for Simon's point #2 is that if you carve voids
into the essentially incompressible rubber, you give it more ways to
bulge outward when pressed against the road and thus waste more energy
through hysteresis.

That is, tread grooves or blocks give the rubber more surface area for
distortion at the contact patch.

Cheers,

Carl Fogel

There's also the allied greater distortion caused by steering, which in
motorcars is effected via slip angles, but on two-wheeled vehicles via
camber thrust.

"Ben C" wrote in message
...
On 2008-02-25, Mike Jacoubowsky wrote:

"Andre Jute" wrote in message
...
| Simon Brooke sent three separate statements
| each requiring explanation:
|
| 1. Contrary to common opinion, for any given rubber compound, (on
| bicycles) slick tyres are better in the wet than tyres with tread.
|
| 2. They also tend to roll slightly better.
|
| 3. Bicycle tyres with tread are only beneficial on soft surfaces, not
| on tarmac.

This has been gone over many, many times in this newsgroup. Rather than
rehash it yet again, try a google search, or simply consult the FAQ-

http://draco.acs.uci.edu/rbfaq/FAQ/8b.13.html

I have a few questions about that post.

It claims that slicks are used in all weather by most street
motorcycles. I'm fairly sure motorbikes for road use don't have slick
tyres and that it's dangerous and illegal to ride them around with bald
or slick tyres. If you watch the Moto GP on TV, as soon it rains they
all start falling off and dashing into the pits for their "wets" (which
have treads).
If you watch their speedos you will notice that Moto gp bikes are going much
faster than you would normally ride your bicycle. (more speed)



I believe bicycles don't aquaplane. Cars rarely aquaplane either, but
relatively un-worn treaded tyres grip much better for basic braking,
traction and cornering as any driver will know from practical
experience. So why is the same effect not possible on a bicycle? I'm
thinking in particular of 47mm road tyres at 60psi or so, rather than
23mm at 110psi.
The same affect is possible in a bicycle, you just have to ride very fast.
(car tyre is a different shape and lower pressure)


The article says, "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". There follows a
parable about window-cleaning squeegees to demonstrate that it's
impossible for a tread to push water out of the way.

But if all that's true, then why are treaded car tyres better? They
certainly aren't harder than the road either.
Car tyres are harder than the road if you think of the water as the road.
That has to be moved out of the way to get to the real road. Bicycle tyres
do this by the shape and pressure. Car tyres need to use tread and the wider
they are the wider the tread needs to be.

aquaplaning is possible in just about anything, it depends on speed, shape
and pressure.




It's claimed that "machines that measure traction show that smooth tyres
corner better on both wet and dry pavement". Does anyone know any more
about these tests, and what sort of tyres were tested?

dabac wrote:

I'll readily accept the statement that a slick tyre has better traction
than a treaded tyre against a smooth surface.
But what if the tread pattern roughly matches the surface structure of
the road surface?

It'd be a bit like having two corrugated surfaces interfacing with each
other, with a lot of protrusions interfering with each other.
Shouldn't that be grippier than one corrugated surface resting agains a
flat surface? - as long as tread courseness "matches" surface
coarseness...

Think about it a little bit. Suppose you wanted to design such a tread.
First, you would want to scale the tread pattern to match the scale of
the surface texture. You could make a casting of the surface and make
your tread the inverse pattern. But of course the pattern is random, so
in actual use it would never align. What happens when it misaligns? Do
you have more or less contact? Do you get any feature engagement? After
answering those questions, you might consider changing the tire tread
pattern scale. Does enlarging or reducing help feature engagement?

The only way you could get real feature engagement would be to have a
regular pattern on the road and a matching pattern on the tire. Then you
would have to have a pattern that would engage in all orientations. Just
consider how difficult it would be to get this to work in even one
direction and what the trade offs would be (grooved tires on grooved roads).

There is at least one example where the contact patch conforms to the
running surfaces -- railroads. A cog railway even gets you both improved
traction and lateral grip.

Roughness on roads is designed to break the film tension of water. Sooth
soled sneakers work well on dry polished rock, or rough wet rock,
treaded sneakers will work a little less well on either.

Fiberglass boat decks usually have a fine, sharp-edged texture molded
in. The best shoes for wet traction have smooth soles. Most of these
soles have siping, which help to prevent trapping a layer of water, but
that's for wet smooth surfaces. It might be possible to make a tread
pattern that "indexed" into the deck pattern, but as far as I know it's
not done, and I doubt that it would be an improvement.

Peter Cole Wrote:
dabac wrote:

I'll readily accept the statement that a slick tyre has better
traction
than a treaded tyre against a smooth surface.
But what if the tread pattern roughly matches the surface structure
of
the road surface?

It'd be a bit like having two corrugated surfaces interfacing with
each
other, with a lot of protrusions interfering with each other.
Shouldn't that be grippier than one corrugated surface resting agains
a
flat surface? - as long as tread courseness "matches" surface
coarseness...

Think about it a little bit. Suppose you wanted to design such a
tread.
First, you would want to scale the tread pattern to match the scale of
the surface texture. You could make a casting of the surface and make
your tread the inverse pattern. But of course the pattern is random,
so
in actual use it would never align. What happens when it misaligns? Do
you have more or less contact? Do you get any feature engagement?
After
answering those questions, you might consider changing the tire tread
pattern scale. Does enlarging or reducing help feature engagement?

The only way you could get real feature engagement would be to have a
regular pattern on the road and a matching pattern on the tire. Then
you
would have to have a pattern that would engage in all orientations.

I like to believe that I HAVE thought a bit about it, and it's not like
I'm claiming it to once and for all solve all traction problems. But
although a 100% match would be as improbable as efficient I wonder if
there isn't a lower degree of surface/tread matching where it would
still offer improved traction.
The perfect misaligment where every ridge meets another ridge must be
as improbable as the perfect alignment where every ridge meets a furrow.
Assuming an intermediate degree of alignment, is it really that easy to
discard the possible influence of geometric interference between surface
and tread after all?


--
dabac

In article
,
Hank wrote:

On Feb 24, 6:13*pm, Andre Jute wrote:
*Simon Brooke sent three separate statements
each requiring explanation:

1. *Contrary to common opinion, for any given rubber compound, (on
bicycles) slick tyres are better in the wet than tyres with tread.

2. They also tend to *roll slightly better.

3. Bicycle tyres with tread are only beneficial on soft surfaces, not
on tarmac.

#s 1 & 3 are obvious on their face.

In the case of 1, slick guarantees more contact with the road. Bike
tires are too narrow to hydroplane, so there's no need for channels to
evacuate water.

As for #3, on soft surfaces, the ground deforms in deference to the
tire. On hard surfaces, the tire must deform in deference to the road.
So a slick tire at pressure low enough to deform (which also increases
the contact patch area) but not bottom out provides the best traction.

I'll let someone else tackle #2, because I don't fully understand the
science of rolling resistance, and won't shame myself by, as the
Russians say, talking out my nose on the subject.

Rolling resistance arises from flexing the tires. The
tires are not entirely elastic and dissipate as heat
some of the energy that went into flexing them. Tires
flex significantly in the side walls and in the tread.
If there is a relief pattern in the tread (e.g. knobs),
additional energy is dissipated flexing the tread. Thin
side walls and thin tread noticiably reduce rolling resistance.

--
Michael Press

Michael Press writes:

Simon Brooke sent three separate statements each requiring
explanation:

1. Contrary to common opinion, for any given rubber compound, (on
bicycles) slick tyres are better in the wet than tyres with
{patterned} tread.

2. They also tend to roll slightly better.

3. Bicycle tyres with {patterned} tread are only beneficial on
soft surfaces, not on tarmac.

#s 1 & 3 are obvious on their face.

In the case of 1, slick guarantees more contact with the road. Bike
tires are too narrow to hydroplane, so there's no need for channels
to evacuate water.

As for #3, on soft surfaces, the ground deforms in deference to the
tire. On hard surfaces, the tire must deform in deference to the
road. So a slick tire at pressure low enough to deform (which also
increases the contact patch area) but not bottom out provides the
best traction.

I'll let someone else tackle #2, because I don't fully understand
the science of rolling resistance, and won't shame myself by, as
the Russians say, talking out my nose on the subject.

Rolling resistance arises from flexing the tires. The tires are not
entirely elastic and dissipate as heat some of the energy that went
into flexing them. Tires flex significantly in the side walls and in
the tread. If there is a relief pattern in the tread (e.g. knobs),
additional energy is dissipated flexing the tread. Thin side walls
and thin tread noticeably reduce rolling resistance.

Even with entirely elastic material, there are hysteretic losses that
dissipate energy (heat) when the material is deformed. The effect can
be felt by stretching a thick rubber band, sensing its temperature by
brining it contact with one's upper lip to make heating and cooling
apparent.

Jobst Brandt