On 25/06/18 11:07, Jeff wrote:
And it is very easy to actually measure if the rotation rate of the wheel
does in fact vary with the distance between the axle and the road.

Yes - the guy in the video did that and there was sod all difference.

Its a very small difference due to belt elasticity thats all.


--
Ideas are more powerful than guns. We would not let our enemies have
guns, why should we let them have ideas?

Josef Stalin

On 25/06/18 11:51, Huge wrote:
On 2018-06-25, Andy Burns wrote:
Huge wrote:

Andy Burns wrote:

there isn't a single distance from the centre of the axle to all
parts of the tyre in contact with the road ... the average distance perhaps?

This is really, really simple. Why are you all making it so
complicated? (It's the *shortest* distance, obviously. Just draw a bloody
diagram.)

The diagram I linked to yesterday seems suitable

http://the-contact-patch.com/book/road/c2020-the-contact-patch#figure-ERr

Because it's wrong. In this context, the relevant dimension is O - Q. How
could it be otherwise? I'm afraid this seems so obvious to me that I cannot
find ways to explain it.


No, I accept that you simply dont have a scientific brain.

You are like te Afrikaaaner I spoke to ocne 'Black people don't have
souls' he said' It was as obvious to him as....this is to you.


--
The New Left are the people they warned you about.

On 25/06/18 12:04, Andy Burns wrote:
Tim Streater wrote:

One revolution of the wheel has to equal one passage of the tire's
circumference along the road (since the tire does not slip around the
rim and assuming no slip on the road). How could it be otherwise?

Talk of "effective radius" is not relevant.

So are saying the circumference remains constant, hence the rpm remains
constant, hence iTPMS cannot work?


No, we are saying that te circumference remains *nearly* constant, and
the difference is due to belt shrinkahe under lower pressure NOT
'reduction in radius' and is of the order of less than a percent for up
to 10% reduction in 'radius'

Has to be so or flat tyres would give *way* out speedo readings


--
The New Left are the people they warned you about.

On 25/06/18 16:27, Andy Burns wrote:
Tim Streater wrote:

Andy Burns wrote:

So are saying the circumference remains constant, hence the rpm
remains constant, hence iTPMS cannot work?

The steel cords may stretch a little, but that's all. Without that, the
circumference *must* stay constant.

The steel belts aren't parallel to the circumference, they're on a low
angle diagonally, so they can bunch-up or space-out with the distortion
of the tyre as it revolves, so the change in circumference can be more
than just you'd get by stretching them, though it still only needs to be
small to be measurable.

I am not sure that is so on a modern radial. Thats ounds like a cross ply.

Oh. SA quck google sdsyas that some tyres are slightly angled tread belt
wise and some are truly circumferential.

--
"And if the blind lead the blind, both shall fall into the ditch".

Gospel of St. Mathew 15:14

On 25/06/18 14:06, Robin wrote:
On 25/06/2018 12:00, Tim Streater wrote:
In article , Huge
wrote:

On 2018-06-25, Andy Burns wrote:
Huge wrote:

Andy Burns wrote:

there isn't a single distance from the centre of the axle to all
parts of the tyre in contact with the road ... the average distance
perhaps?

This is really, really simple. Why are you all making it so
complicated? (It's the *shortest* distance, obviously. Just draw a
bloody
diagram.)

The diagram I linked to yesterday seems suitable

http://the-contact-patch.com/book/road/c2020-the-contact-patch#figure-ERr


Because it's wrong. In this context, the relevant dimension is O -
Q. How
could it be otherwise?

One revolution of the wheel has to equal one passage of the tire's
circumference along the road (since the tire does not slip around the
rim and assuming no slip on the road). How could it be otherwise?

Talk of "effective radius" is not relevant.


If by "effective radius" you mean the rolling radius it is the only
relevant measure to combine with the angular velocity in order to arrive
at the speed of the vehicle[1].Â* If you dispute that please post your
equation.

Or of course you could admit that by circumference you mean the rolling
circumference - defined as 2 x Pi x the rolling radius - which changes
with pressure.



No, the 'rolling radius' is th *circumference* divided by 2 x PI and HAS
NO relationship with how far the axle is from the road.

It doesnt change as you go over a slpeeing policeman. :-)


--
Future generations will wonder in bemused amazement that the early
twenty-first centurys developed world went into hysterical panic over a
globally average temperature increase of a few tenths of a degree, and,
on the basis of gross exaggerations of highly uncertain computer
projections combined into implausible chains of inference, proceeded to
contemplate a rollback of the industrial age.

Richard Lindzen

On Mon, 25 Jun 2018 18:37:40 +0100, The Natural Philosopher
wrote:

On 25/06/18 12:04, Andy Burns wrote:
Tim Streater wrote:

One revolution of the wheel has to equal one passage of the tire's
circumference along the road (since the tire does not slip around the
rim and assuming no slip on the road). How could it be otherwise?

Talk of "effective radius" is not relevant.

So are saying the circumference remains constant, hence the rpm remains
constant, hence iTPMS cannot work?


No, we are saying that te circumference remains *nearly* constant, and
the difference is due to belt shrinkahe under lower pressure

Ah, here it begins ... first we had 'it can't change' to 'only expand
with pressure' and now we have 'contract with shrinkage'. ;-)

NOT
'reduction in radius' and is of the order of less than a percent for up
to 10% reduction in 'radius'

Oh well, we will get there soon ...

Has to be so or flat tyres would give *way* out speedo readings

Yeah, something we would all know, watching the speedo whilst driving
on flat tyres. ;-)

Cheers, T i m

On Mon, 25 Jun 2018 18:31:40 +0100, The Natural Philosopher
wrote:

On 25/06/18 10:58, Huge wrote:
On 2018-06-25, Andy Burns wrote:
Dave Plowman wrote:

Huge wrote:

The - Bits - Of - The - Tyre - Not - In - Contact - With - The - Road -
Are - Irrelevant. The - Only - Thing - That - Matters - Is - The -
Diameter - Of - The - Circle - Whose - Radius - Is - The - Distance -
From - The - Axle - To. The - Road.

You should have used caps, Huge. For those whose physics are still at
kindergarten level.

Except there isn't a single distance from the centre of the axle to all
parts of the tyre in contact with the road ... the average distance perhaps?

Oh, FFS. This is really, really simple. Why are you all making it so
complicated? (It's the *shortest* distance, obviously. Just draw a bloody
diagram.)


Because it is not simple. Only you are simple. It is in fact fiendishly
complicated.

You seem to be making it so.

And the short cut is to forget radius and think only of
circumgference If you think in terms of radius you will get it all wrong

We don't, you do.

Because the rim of the wheel is moving slower than you think,

What ... 'slower than someone thinks' ... it looks like it's all
unraveling now eh Turnip? ;-(

because
the tyre is flexing as it goes round.

No, who would have thought. I wonder why someone didn't state that
early on?

Cheers, T i m

On Mon, 25 Jun 2018 18:26:00 +0100, The Natural Philosopher
wrote:

snip

Huges simple minded O level fizzix cant cope with the reality of an
elastically coupled non-circular tyre attached in a non slip fashion to
a wheel.

It works better than anything you have come up with so far ...

This is the sort of thinking that creates climate Beleivers -

Hey, I believe we have a climate?

people who
THINK they know a little bit of science ....

And as my Dad used to say (probably about you), 'Most of the harm done
in this world isn't done by people who don't know but by people who
don't know they don't know'.

It will be interesting to see how you finally get out of this one.

'That's what I meant / have been saying all along' is my best bet. ;-)

Cheers, T i m

On Mon, 25 Jun 2018 18:16:53 +0100, The Natural Philosopher
wrote:

snip

There are no substantial changes. Ther is a very small change due to
elsatyicity of the tread belt.

Ooo, we have belts that stretch, belts that shrink and now belts that
are 'elastic', we are getting there just very s l o w l y.

You know this is true otherwise speedos would
be massively variable with tyre pressure and wheel loading
They are not.

'Massively'? Who is talking massively on any of this (apart from them
being good weasel words).

Cheers, T i m

On Mon, 25 Jun 2018 18:20:24 +0100, "NY" wrote:

snip

But if you were to label part of the tread with a line continuing radially
up the sidewall to the centre, that line would not remain a straight line;
it would curve one way as the labelled part approaches the road surface and
then the other way as it leaves it; this happens because the plies of the
steel belt move towards or away from each other as the tyre rotates. Not by
a noticeable amount; probably by an amount that is hard even to measure.

+1

The
tyre is no longer a perfect circle but a circle with a flat on the side
which is contact with the road at this precise instant.

Yup.

So, this could be easy to measure.

With a correctly inflated car tyre on the car and parked on a
smoothish / flat surface ... jack a wheel up and measure the
circumference with a tape measure. Lower the car back onto it's wheel,
keeping the tape in place and once back on the ground, check the tape
again.

Lower the tyre pressure a reasonable percent and measure again.

Cheers, T i m

On Mon, 25 Jun 2018 18:42:09 +0100, The Natural Philosopher
wrote:

snip


Oh. SA quck google sdsyas that some tyres are slightly angled tread belt
wise

Ooops, here we go, another step closer! ;-)

and some are truly circumferential.

Only the bead AFAIC.

Cheers, T i m

On 25/06/2018 18:45, The Natural Philosopher wrote:
On 25/06/18 14:06, Robin wrote:
On 25/06/2018 12:00, Tim Streater wrote:
In article , Huge
wrote:

On 2018-06-25, Andy Burns wrote:
Huge wrote:

Andy Burns wrote:

there isn't a single distance from the centre of the axle to all
parts of the tyre in contact with the road ... the average distance
perhaps?

This is really, really simple. Why are you all making it so
complicated? (It's the *shortest* distance, obviously. Just draw a
bloody
diagram.)

The diagram I linked to yesterday seems suitable

http://the-contact-patch.com/book/road/c2020-the-contact-patch#figure-ERr


Because it's wrong. In this context, the relevant dimension is O -
Q. How
could it be otherwise?

One revolution of the wheel has to equal one passage of the tire's
circumference along the road (since the tire does not slip around the
rim and assuming no slip on the road). How could it be otherwise?

Talk of "effective radius" is not relevant.


If by "effective radius" you mean the rolling radius it is the only
relevant measure to combine with the angular velocity in order to
arrive at the speed of the vehicle[1].Â* If you dispute that please
post your equation.

Or of course you could admit that by circumference you mean the
rolling circumference - defined as 2 x Pi x the rolling radius - which
changes with pressure.



No, the 'rolling radius' is th *circumference* divided by 2 x PI and HAS
NO relationship with how far the axle is from the road.

It doesnt change as you go over a slpeeing policeman.Â* :-)


If you read again my posts you will see I said nothing about the how far
the axle is from the road. I was merely asking why people seem to have
so much difficulty with


dynamic rolling radius = (speed)/(angular velocity)

--
Robin
reply-to address is (intended to be) valid

"The Natural Philosopher" wrote in message
news
On 25/06/18 12:04, Andy Burns wrote:
Tim Streater wrote:

One revolution of the wheel has to equal one passage of the tire's
circumference along the road (since the tire does not slip around the
rim and assuming no slip on the road). How could it be otherwise?

Talk of "effective radius" is not relevant.

So are saying the circumference remains constant, hence the rpm remains
constant, hence iTPMS cannot work?


No, we are saying that te circumference remains *nearly* constant, and the
difference is due to belt shrinkahe under lower pressure NOT 'reduction in
radius' and is of the order of less than a percent for up to 10% reduction
in 'radius'

Has to be so or flat tyres would give *way* out speedo readings

I presume when you say "flat" you mean a tyre that is below the rated
pressure but still maintains roughly the same profile. I tend to think of
that as "low", and "flat" to mean a tyre that has bugger-all air in it, so
the wheel rim is rubbing on the inside of the tread surface, doing untold
damage to the tyre.

Having driven on a low tyre (to get me to a garage that I knew was only half
a mile away, to save the hassle of changing the wheel in heavy traffic) I
have no idea by how much the speedo may or may not have been overreading.
Short of checking it with a GPS, it's very difficult to tell.

I have once driven on a totally knackered tyre for about a hundred yards,
when a car pulled out and I had to swerve to avoid it, hitting the kerb
harder than I would have liked. The sidewall burst. As it was immediately
before a roundabout, with no way of traffic getting me round me, I decided
that since the tyre was buggered, I couldn't do any more damage. Once I'd
stopped safely beyond the roundabout, my fun really began because I
discovered that the wire cage which held the spare tyre had seized up: there
was a long bolt that went through the floor of the boot into a nut on the
cage: and that was rusted up. I actually had to call out the RAC for help
with changing a wheel, simply to get at the spare. The pillocks who made
that car had out a very broad semi-cylindrical nick in the head of the bolt
which you were supposed to turn with the flattened end of the wheelbrace -
utterly useless for getting any purchase if the bolt had seized. If only the
bolt head had been a proper hexagon the same size as the wheelnuts, it would
have been trivial to undo it.

The Natural Philosopher wrote:

the guy in the video did that

He only measured it once, and he did is very very slowly, would the
deformation of the tyre behave differently at a higher speed?

On Mon, 25 Jun 2018 18:02:49 +0100, The Natural Philosopher
wrote:

On 24/06/18 08:03, Richard wrote:
On 23/06/18 17:01, The Natural Philosopher wrote:

No.
Since no wheel is circular using radious as a concept is plain wrong.
At best you can calcualate a '*radius it would be if it were round*,'
from the actual circumference.

The use of radius is completely right.
The circumference doesn't change. The centre of the instantaneous circle
moves closer to the radius.
The tyre is a three dimensional structure and this debate is being
conducted in a two dimensional manner.


I hope no one ebver emp;loys you in an engineering capacity.

The use of radius is meaningless. The the tyre is not round.

That's why 'most people' that know what they are talking about use the
terms 'rolling radius' (effective loaded radius) and have done for
years, and all without your understanding or permission!

From this dynamic value you can extrapolate the rolling circumference
or even measure it (as it's a real thing of course).

Plug an OBD reader into your ABS equipped car and pickup one of the
sensor ring outputs.

Measure the unloaded circumference of the tyre.

Use the output of the ABS ring to count the wheel revs, calculate the
theoretical distance traveled and compare that with a GPS or road
marked value. Report back here with your findings. ;-)

Cheers, T i m

"NY" wrote in message
...
"Jeff" wrote in message
...
Yes, but it is the distance between the axle and the road
that determines the rotation rate.

Why?

Because that's how the physics works. And that should be obvious from
what happens with wheels with no tyre, with different diameter wheels.

Long time since 'O' level maths but I suspect the relationship between
the radius and the perimeter only works for a perfect circle.

Irrelevant to what determines the rotation rate of the wheel.

True, but the easiest way to visualise the rotation rate for a unit
distance travelled is to divide the distance travelled by the
circumference to give the number of wheel revolutions.

However... it all hinges on what the *effective* circumference is: it is
the circumference of an imaginary circle with the same radius as the
distance between centre of the axle and road surface, which will be less
than the no-load radius because the tyre is slightly flattened where it
comes in contact with the road.

I presume this means that if you took a piece of string and passed it
round the circumference of a tyre this value would be smaller than the
no-load circumference because the part that is in contact with the road
will be a flat rather than a curved profile.

I think that is unlikely given that you don't see that effect with a steel
radial although it is certainly possible that Tim's parallelogram effect
means that it isnt as rigid as you might think.

This assumes that the radius of the rest
of the tyre doesn't increase significantly when a load is applied to the
tyre - presumably this is constrained by the steel reinforcing belts in
the tyre.


I wonder how much smaller the in-contact radius is than the no-load
radius: what sort of proportion is the reduction, typically? I'll have to
measure the actual distance from the centre of the hubcap to the ground,
and then jack the wheel up until it first touches the road and measure
again. Note that you can't measure to a part of the car body because of
compression of springs :-)

"Tim Streater" wrote in message
.. .
In article , Huge
wrote:

On 2018-06-25, Andy Burns wrote:
Huge wrote:

Andy Burns wrote:

there isn't a single distance from the centre of the axle to all
parts of the tyre in contact with the road ... the average distance
perhaps?

This is really, really simple. Why are you all making it so
complicated? (It's the *shortest* distance, obviously. Just draw a
bloody
diagram.)

The diagram I linked to yesterday seems suitable

http://the-contact-patch.com/book/road/c2020-the-contact-patch#figure-ERr

Because it's wrong. In this context, the relevant dimension is O - Q. How
could it be otherwise?

One revolution of the wheel has to equal one passage of the tire's
circumference along the road (since the tire does not slip around the
rim and assuming no slip on the road). How could it be otherwise?

Talk of "effective radius" is not relevant.

Yes it is when that is what determines the rotation rate of the wheel
as can be seen with different diameter wheels with no tyre.

"The Natural Philosopher" wrote in message
news
On 24/06/18 22:18, Jeff wrote:


And yet if you consider a solid wheel, no tyre, it is the distance
between the axle and the road that determines the rate at which
it rotates at the same speed of the car over the ground.

Yes.

So when
a wheel with tyre sees a reduction in the distance between the
axle and the road due to a lower pressure in the tyre, you get
the same change in the rotation rate of the wheel which is
easy to measure with the ABS sensor on that wheel.

No. Once yopu put a non circular tyre on, you vannot talk about radius.

The only distance that matters is the distance between the axle and
the road. That is what determines the rotation rate of the wheel.

Yes, it is better not to call that the radius.

What counts is the distance round whatever shape the tread is.

No, what matters is the distance between the axle and the road
as you agreed with the first paragraph of mine.

Al;l of
that has to be in contact with the road during one wheel revolution unelss
the tyre slips on the rim

Yes, but that isn't what determines the rotation rate of the wheel
that the ABS sensor is measuring.

On 25/06/2018 18:12, NY wrote:
"The Natural Philosopher" wrote in message
news
No. The effective radious first of all is almost ********. But if you
mean te circumferenmce divided by 2 PI then that will only change with
pressure, as the belts strech, Not with loading.

Otherwise p[eole would be travvling 30% slower when their tyres were
flat, for the same speedo reading

They *will* be travelling slower - you've got that right. But not by
anywhere near as much as 30%.

60 profile tyres on 15 inch rims will be about 30% slower on flat tyres
once the tread falls off.

On 25/06/2018 18:47, T i m wrote:

8

Has to be so or flat tyres would give *way* out speedo readings

Yeah, something we would all know, watching the speedo whilst driving
on flat tyres. ;-)

Do you think he has worked out that tyres aren't flat even when at zero
pressure if the wheel is spinning. Maybe he has never swung a weight on
a bit of string?

On 25/06/2018 18:45, The Natural Philosopher wrote:

No, the 'rolling radius' is th *circumference* divided by 2 x PI and HAS
NO relationship with how far the axle is from the road.

It doesnt change as you go over a slpeeing policeman.Â* :-)



Oh, it does. It even changes when you go over the painted lines.
Maybe you are thinking of cart wheels with steel tyres and not knobbly
bits of rubber stuck to a flexible belt?

On 25/06/2018 19:40, Andy Burns wrote:
The Natural Philosopher wrote:

the guy in the video did that

He only measured it once, and he did is very very slowly, would the
deformation of the tyre behave differently at a higher speed?

Its all different when its on a car rather than say a rolling road.
On a car as you go faster the load tangential to the contact area
increases with speed due to air resistance.

Also the tyre will become more circular as the speed goes up.

On 25/06/2018 18:08, The Natural Philosopher wrote:
On 24/06/18 22:18, Jeff wrote:


And yet if you consider a solid wheel, no tyre, it is the distance
between the axle and the road that determines the rate at which
it rotates at the same speed of the car over the ground.

Yes.

Â*So when
a wheel with tyre sees a reduction in the distance between the
axle and the road due to a lower pressure in the tyre, you get
the same change in the rotation rate of the wheel which is
easy to measure with the ABS sensor on that wheel.

No. Once yopu put a non circular tyre on, you vannot talk about radius.

What counts is the distance round whatever shape the tread is. Al;l of
that has to be in contact with the road during one wheel revolution
unelss the tyre slips on the rim





Or it slips on the road like it does.

On 25/06/18 22:42, dennis@home wrote:
On 25/06/2018 18:08, The Natural Philosopher wrote:
On 24/06/18 22:18, Jeff wrote:


And yet if you consider a solid wheel, no tyre, it is the distance
between the axle and the road that determines the rate at which
it rotates at the same speed of the car over the ground.

Yes.

Â*Â*So when
a wheel with tyre sees a reduction in the distance between the
axle and the road due to a lower pressure in the tyre, you get
the same change in the rotation rate of the wheel which is
easy to measure with the ABS sensor on that wheel.

No. Once yopu put a non circular tyre on, you vannot talk about radius.

What counts is the distance round whatever shape the tread is. Al;l of
that has to be in contact with the road during one wheel revolution
unelss the tyre slips on the rim





Or it slips on the road like it does.

its amazing.

There is almost perfect correlation between people who believe in the
european Union and people who beleive a flat tyre speeds up by the
change in apparent radius.

I bet thr is a strong correlation s ell with peopple who believe in
catastrophic man made climate change.

On 25/06/18 18:02, The Natural Philosopher wrote:
On 24/06/18 08:03, Richard wrote:
On 23/06/18 17:01, The Natural Philosopher wrote:

No.
Since no wheel is circular using radious as a concept is plain wrong.
At best you can calcualate a '*radius it would be if it were round*,'
from the actual circumference.

The use of radius is completely right.
The circumference doesn't change. The centre of the instantaneous
circle moves closer to the radius.
The tyre is a three dimensional structure and this debate is being
conducted in a two dimensional manner.


I hope no one ebver emp;loys you in an engineering capacity.

I hope so too, as I am not an engineer.


The use of radius is meaningless. The the tyre is not round.

It doesn't have to be. The radius is the distance between the centre of
the object and a point on the perimeter (circumference). In our case,
the point closest to the centre.
20P and 50P coins have a constant diameter despite not being circular.


Go and get a technical education

I did, but am always learning.

"Tjoepstil" wrote in message
news
On 25/06/18 22:42, dennis@home wrote:
On 25/06/2018 18:08, The Natural Philosopher wrote:
On 24/06/18 22:18, Jeff wrote:


And yet if you consider a solid wheel, no tyre, it is the distance
between the axle and the road that determines the rate at which
it rotates at the same speed of the car over the ground.

Yes.

So when
a wheel with tyre sees a reduction in the distance between the
axle and the road due to a lower pressure in the tyre, you get
the same change in the rotation rate of the wheel which is
easy to measure with the ABS sensor on that wheel.

No. Once yopu put a non circular tyre on, you vannot talk about radius.

What counts is the distance round whatever shape the tread is. Al;l of
that has to be in contact with the road during one wheel revolution
unelss the tyre slips on the rim





Or it slips on the road like it does.

its amazing.

There is almost perfect correlation between people who believe in the
european Union and people who beleive a flat tyre speeds up by the change
in apparent radius.

There isn't actually and the total number who have commented isn't high
enough for what correlation you claim to see to be significant either.

I bet thr is a strong correlation s ell with peopple who believe in
catastrophic man made climate change.

You've lost that bet too.

On Mon, 25 Jun 2018 22:13:38 +0100, "dennis@home"
wrote:

On 25/06/2018 18:47, T i m wrote:

8

Has to be so or flat tyres would give *way* out speedo readings

Yeah, something we would all know, watching the speedo whilst driving
on flat tyres. ;-)

Do you think he has worked out that tyres aren't flat even when at zero
pressure if the wheel is spinning.

I think you would have to be going some though for that to me any use
ITRW. ;-)

Maybe he has never swung a weight on
a bit of string?

I'm sure he's swung the lead a few times. ;-)

Cheers, T i m

On 25/06/18 21:39, Jeff wrote:


"The Natural Philosopher" wrote in message
news
On 24/06/18 22:18, Jeff wrote:


And yet if you consider a solid wheel, no tyre, it is the distance
between the axle and the road that determines the rate at which
it rotates at the same speed of the car over the ground.

Yes.

Â*So when
a wheel with tyre sees a reduction in the distance between the
axle and the road due to a lower pressure in the tyre, you get
the same change in the rotation rate of the wheel which is
easy to measure with the ABS sensor on that wheel.

No. Once yopu put a non circular tyre on, you vannot talk about radius.

The only distance that matters is the distance between the axle and
the road. That is what determines the rotation rate of the wheel.

Yes, it is better not to call that the radius.

What counts is the distance round whatever shape the tread is.

No, what matters is the distance between the axle and the road
as you agreed with the first paragraph of mine.


That was in a rooundwheel case, in which case the two are absolutely
related by the formula 2*PI*R = C.

My point is that once te tyre is on and deforming, that relationship has
no validity or meaning. I applies to circle only. And the flatter the
tyre is the less circular it is.

YOU and your ilk are claiming that this means that the thing that is
most important is the radius, even though a non circular object has no
constant radius. It DOES however have a circumference. That doesn't change.





Al;l of
that has to be in contact with the road during one wheel revolution
unelss the tyre slips on the rim

Yes, but that isn't what determines the rotation rate of the wheel
that the ABS sensor is measuring.

It is.


--
Religion is regarded by the common people as true, by the wise as
foolish, and by the rulers as useful.

(Seneca the Younger, 65 AD)

On 26/06/18 06:31, Richard wrote:
On 25/06/18 18:02, The Natural Philosopher wrote:
On 24/06/18 08:03, Richard wrote:
On 23/06/18 17:01, The Natural Philosopher wrote:

No.
Since no wheel is circular using radious as a concept is plain
wrong. At best you can calcualate a '*radius it would be if it were
round*,' from the actual circumference.

The use of radius is completely right.
The circumference doesn't change. The centre of the instantaneous
circle moves closer to the radius.
The tyre is a three dimensional structure and this debate is being
conducted in a two dimensional manner.


I hope no one ebver emp;loys you in an engineering capacity.

I hope so too, as I am not an engineer.


The use of radius is meaningless. The the tyre is not round.

It doesn't have to be. The radius is the distance between the centre of
the object and a point on the perimeter (circumference). In our case,
the point closest to the centre.

No, it is not.

20P and 50P coins have a constant diameter despite not being circular.

No, they do not.



Go and get a technical education

I did, but am always learning.

No, you are not.

--
"When a true genius appears in the world, you may know him by this sign,
that the dunces are all in confederacy against him."

Jonathan Swift.

In article ,
Jeff wrote:
No. Once yopu put a non circular tyre on, you vannot talk about radius.

The only distance that matters is the distance between the axle and
the road. That is what determines the rotation rate of the wheel.

Yes, it is better not to call that the radius.

Radius between centre of wheel and point of contact to the road surface.
That is the only relevant part as regards how far the car travels per
rotation of the wheel. Not any theoretical amount.

--
*Failure is not an option. It's bundled with your software.

Dave Plowman London SW
To e-mail, change noise into sound.

On 26/06/2018 09:06, The Natural Philosopher wrote:
On 26/06/18 06:31, Richard wrote:

20P and 50P coins have a constant diameter despite not being circular.

No, they do not.


They do for the normal meaning of "diameter" (which is not confined
circles, spheres or other n-spheres)


--
Robin
reply-to address is (intended to be) valid

"Robin" wrote in message
...
On 26/06/2018 09:06, The Natural Philosopher wrote:
On 26/06/18 06:31, Richard wrote:

20P and 50P coins have a constant diameter despite not being circular.

No, they do not.


They do for the normal meaning of "diameter" (which is not confined
circles, spheres or other n-spheres)

I must admit, I would tend to confine the word "diameter" to circular (or
spherical) objects. But let's leave semantics aside.

I had never realised that the flats on a 20p or 50p coin were arranged so
the distance between one edge and the other, for any line that goes through
the centre, was always the same, irrespective of which part of the flat or
point the line happened to go through and even though the middle of that
line may not always coincide with the centre of the coin.

Do all polygons with an odd number of sides have the property, or is it
unique to heptagons (7 sides)?

"The Natural Philosopher" wrote in message
news
YOU and your ilk are claiming that this means that the thing that is most
important is the radius, even though a non circular object has no constant
radius. It DOES however have a circumference. That doesn't change.

I think the only important thing is the the distance between the axle and
the point which touches the ground ("the effective radius", as some people
have called it) is constant as the tyre rotates - as indeed it must be,
otherwise you'd have a very bumpy ride :-) The radius at all other points on
the tyre which are not touching the ground is not important.

"The Natural Philosopher" wrote in message
news
On 25/06/18 21:39, Jeff wrote:


"The Natural Philosopher" wrote in message
news
On 24/06/18 22:18, Jeff wrote:


And yet if you consider a solid wheel, no tyre, it is the distance
between the axle and the road that determines the rate at which
it rotates at the same speed of the car over the ground.

Yes.

So when
a wheel with tyre sees a reduction in the distance between the
axle and the road due to a lower pressure in the tyre, you get
the same change in the rotation rate of the wheel which is
easy to measure with the ABS sensor on that wheel.

No. Once yopu put a non circular tyre on, you vannot talk about radius.

The only distance that matters is the distance between the axle and
the road. That is what determines the rotation rate of the wheel.

Yes, it is better not to call that the radius.

What counts is the distance round whatever shape the tread is.

No, what matters is the distance between the axle and the road
as you agreed with the first paragraph of mine.


That was in a rooundwheel case, in which case the two are absolutely
related by the formula 2*PI*R = C.

My point is that once te tyre is on and deforming, that relationship has
no validity or meaning. I applies to circle only. And the flatter the tyre
is the less circular it is.

Its still the distance that determines the rotation rate of the wheel.

Yes, I can see that your line about the circumference of the tyre
that determines the rotation rate of the tyre, but given that it is
so easy to determine whether it is the circumference or the
distance between the axle and the road that determines the
rotation rate experimentally, IMO there isnt any point in
proclaiming which it actually is, time to actually measure it.

YOU and your ilk are claiming that this means that the thing that is most
important is the radius, even though a non circular object has no constant
radius.

No one said anything about any constant radius.

It DOES however have a circumference. That doesn't change.

And yet the system that uses the ABS rotation rate does work
for a lot more than just a flat tyre.




Al;l of
that has to be in contact with the road during one wheel revolution
unelss the tyre slips on the rim

Yes, but that isn't what determines the rotation rate of the wheel
that the ABS sensor is measuring.

It is.

"Dave Plowman (News)" wrote in message
...
Radius between centre of wheel and point of contact to the road surface.
That is the only relevant part as regards how far the car travels per
rotation of the wheel. Not any theoretical amount.

At first I thought that it would be the minimum radius, measured to the
centre of the contact patch, which would be important. But having seen the
diagrams that were referred to earlier in the thread, I now wonder whether
the effective radius is somewhere between the minimum and the no-load
radius, to take into account the fact that the radius varies depending on
whereabouts on the contact patch you measure it.


Part of the problem with all this discussion is that we are talking about a
very small variation between loaded radius and no-load radius, which makes
it difficult to measure in the real world with a crude
tyre-on-a-road-surface measurement. The chances are that if you measure how
far a tyre travels for a given number of revolutions, firstly with
negligible load and/or pumped-up tyre, and secondly with a loaded and/or
half-way flat tyre, you would find it difficult to see any difference that
was larger than experimental error. This assumes that you measure a fairly
small number of rotations to keep the total distance travelled down to a
length that can easily be measured.

I don't really have a feel for how much of a difference there is for a
typical tyre, and therefore how many revolutions you'd need to measure
before you observed a difference that was noticeable.

All you can do is to try to make the difference as large as possible (deep,
high-profile tyre; significantly under-inflated - to maximise the amount of
flat on the contact side of the tyre) in order to demonstrate that there
*is* a difference in distance travelled per revolution compared with a truly
circular tyre.

"Dave Plowman (News)" wrote in message
...
In article ,
Jeff wrote:
No. Once yopu put a non circular tyre on, you vannot talk about radius.

The only distance that matters is the distance between the axle and
the road. That is what determines the rotation rate of the wheel.

Yes, it is better not to call that the radius.

Radius between centre of wheel and point of contact to the road surface.
That is the only relevant part as regards how far the car travels per
rotation of the wheel. Not any theoretical amount.

Yes, but you also have a problem with explaining why it isn't the
circumference of the tyre which doesn’t change much isnt what
determines the rotation rate of the wheel.

On 26/06/2018 10:40, NY wrote:
"Robin" wrote in message
...
On 26/06/2018 09:06, The Natural Philosopher wrote:
On 26/06/18 06:31, Richard wrote:

20P and 50P coins have a constant diameter despite not being circular.

No, they do not.


They do for the normal meaning of "diameter" (which is not confined
circles, spheres or other n-spheres)

I must admit, I would tend to confine the word "diameter" to circular
(or spherical) objects. But let's leave semantics aside.

Fair enough - but the general meaning of "diameter" does apply more
widely. And "diameter" is a lot shorter than eg "the distance between
one edge and the other for a line that goes through the centre"

I had never realised that the flats on a 20p or 50p coin were arranged
so the distance between one edge and the other, for any line that goes
through the centre, was always the same, irrespective of which part of
the flat or point the line happened to go through and even though the
middle of that line may not always coincide with the centre of the coin.

I'm old enough to have "done" the design of the original 50p coin at
school before it was in circulation

Do all polygons with an odd number of sides have the property, or is it
unique to heptagons (7 sides)?

I _think_ it's possible to achieve it with any odd number of corners but
couldn't tell you the parameters that can be fiddled with.



--
Robin
reply-to address is (intended to be) valid

NY wrote:

I must admit, I would tend to confine the word "diameter" to circular
(or spherical) objects. But let's leave semantics aside.

the usual phrase is 'curves of constant width', but in real terms (e.g.
a coin mechanism measuring coins) they do have a constant diameter, but
a varying radius.

I had never realised that the flats on a 20p or 50p coin were arranged
so the distance between one edge and the other, for any line that goes
through the centre, was always the same

Never play with multiple 50ps and two rulers at school?

Do all polygons with an odd number of sides have the property, or is it
unique to heptagons (7 sides)?

No, its a class of Reuleaux prisms, even 'better' are solids of constant
width

https://www.youtube.com/watch?v=2eUWT9cI23o

"Andy Burns" wrote in message
...
NY wrote:

I must admit, I would tend to confine the word "diameter" to circular (or
spherical) objects. But let's leave semantics aside.

the usual phrase is 'curves of constant width', but in real terms (e.g. a
coin mechanism measuring coins) they do have a constant diameter, but a
varying radius.

I had never realised that the flats on a 20p or 50p coin were arranged so
the distance between one edge and the other, for any line that goes
through the centre, was always the same

Never play with multiple 50ps and two rulers at school?

No. I must have missed out on that bit of geometry. Tell me mo I'm
intrigued. I've lived with decimal coins for 47 years and never knew that
20p and 50p coins had constant diameter. I realised that the sides are
slightly curved rather than being flat, but not that the curves were so
arranged as to create a constant width object.

It's just the sort of thing that my old maths teacher (who taught me from
from 1974-77) would have revelled in, so I wonder why he never mentioned it.

Do all polygons with an odd number of sides have the property, or is it
unique to heptagons (7 sides)?

No, its a class of Reuleaux prisms, even 'better' are solids of constant
width

https://www.youtube.com/watch?v=2eUWT9cI23o

Yes, "the concept that something could roll but not be round totally messes
with your head" :-)

I hadn't realised that the rotor of a Wankel engine was a constant width
shape, only that it was an equilateral triangle with curved sides. Indeed I
thought that the sides were only curved to make the corners slightly less
sharp and so reduce the stress on each corner.

On 25/06/2018 15:05, NY wrote:
"Andy Burns" wrote in message
...
The TPMS operates over a longer period of time, probably minutes
rather than seconds, so over many revolutions of the wheel, likely the
numbers will get averaged out before it decides one wheel is turning
faster than the others enough to flag it up.

It *has* to integrate over a fairly long time and number of rotations to
avoid it being triggered every time the car turns a corner and the outer
wheel rotates faster than the inner wheel. I would imagine (and I've not
done the calculations) that the difference in rotational speed between
inner and outer wheel on a bend will be significantly more than the
difference in rotational speed between a correctly-inflated and an
under-inflated wheel, so any TPMS has to average out this large
difference in order to be able to detect a much smaller one.
Hmm. Wonder if drivers in Milton Keynes have problems with over-zealous
triggering of TPMS?