https://www.youtube.com/watch?v=_2l5bOhHNxU

Answer. not by very much, if at all.

This seems to be a perpetual urban myth.

It tyre pressure sensors are using this, it has to be a very very
complicated bit of software to detect - say - less than 1% change in RPM
relative to the other wheels.


--
"When one man dies it's a tragedy. When thousands die it's statistics."

Josef Stalin

"The Natural Philosopher" wrote in message
news
https://www.youtube.com/watch?v=_2l5bOhHNxU

Answer. not by very much, if at all.

But the radius clearly does vary significantly.

This seems to be a perpetual urban myth.

It can't be given that Andy and others have had a number
of warnings that have turned out to be accurate every time.

It tyre pressure sensors are using this, it has to be a very very
complicated bit of software to detect - say - less than 1% change in RPM
relative to the other wheels.

Yes, but that isn't hard to measure when its relative to other wheels.

On 23/06/18 07:08, Jeff wrote:


"The Natural Philosopher" wrote in message
news
https://www.youtube.com/watch?v=_2l5bOhHNxU

Answer. not by very much, if at all.

But the radius clearly does vary significantly.

This seems to be a perpetual urban myth.

It can't be given that Andy and others have had a number
of warnings that have turned out to be accurate every time.


It tyre pressure sensors are using this, it has to be a very very
complicated bit of software to detect - say - less than 1% change in
RPM relative to the other wheels.

Yes, but that isn't hard to measure when its relative to other wheels.

A piece of online research
[https://one.nhtsa.gov/cars/rules/rul...prmonsys.html]
showed that relative wheel rotation was pretty crap at detecting low
tyre pressures especially in all 4 wheels or 2 wheels on the same side
(= I am going round and round in circles!)

Hence the move to in wheel sensors.

I am notr syoing it doesn't work, just that it relies on some pretty
iffy interpreation of very small differences in road speed.

Tyre tread belts do strech under inflation, but not by much. The radius
is completely irrelevant as a road weheel is not, in use, round and does
not have a 'radius.'



--
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

"The Natural Philosopher" wrote in message
news
On 23/06/18 07:08, Jeff wrote:


"The Natural Philosopher" wrote in message
news
https://www.youtube.com/watch?v=_2l5bOhHNxU

Answer. not by very much, if at all.

But the radius clearly does vary significantly.

This seems to be a perpetual urban myth.

It can't be given that Andy and others have had a number
of warnings that have turned out to be accurate every time.


It tyre pressure sensors are using this, it has to be a very very
complicated bit of software to detect - say - less than 1% change in RPM
relative to the other wheels.

Yes, but that isn't hard to measure when its relative to other wheels.

A piece of online research
[https://one.nhtsa.gov/cars/rules/rul...prmonsys.html]
showed that relative wheel rotation was pretty crap at detecting low tyre
pressures especially in all 4 wheels or 2 wheels on the same side (= I am
going round and round in circles!)

Hence the move to in wheel sensors.

I am notr syoing it doesn't work, just that it relies on some pretty iffy
interpreation of very small differences in road speed.

Tyre tread belts do strech under inflation, but not by much. The radius is
completely irrelevant as a road weheel is not, in use, round and does not
have a 'radius.'

Of course it does at the only place that matters, between the axle and
the road.

In message , Jeff
writes


"The Natural Philosopher" wrote in message
news
On 23/06/18 07:08, Jeff wrote:


"The Natural Philosopher" wrote in message
news https://www.youtube.com/watch?v=_2l5bOhHNxU

Answer. not by very much, if at all.

But the radius clearly does vary significantly.

This seems to be a perpetual urban myth.

It can't be given that Andy and others have had a number
of warnings that have turned out to be accurate every time.


It tyre pressure sensors are using this, it has to be a very very
complicated bit of software to detect - say - less than 1% change in
RPM relative to the other wheels.

Yes, but that isn't hard to measure when its relative to other wheels.

A piece of online research
[https://one.nhtsa.gov/cars/rules/rul...prmonsys.html]
showed that relative wheel rotation was pretty crap at detecting low
tyre pressures especially in all 4 wheels or 2 wheels on the same
side (= I am going round and round in circles!)

Hence the move to in wheel sensors.

I am notr syoing it doesn't work, just that it relies on some pretty
iffy interpreation of very small differences in road speed.

Tyre tread belts do strech under inflation, but not by much. The
radius is completely irrelevant as a road weheel is not, in use,
round and does not have a 'radius.'

Of course it does at the only place that matters, between the axle and
the road.

I've been thinking that but... unless the effective circumference is
changed, the tread in contact with the road surface will not alter.
Steel bracing etc. as mentioned above.

Maybe there is some perceptible scrubbing going on.


--
Tim Lamb

Tim Lamb wrote:

I've been thinking that but... unless the effective circumference is
changed, the tread in contact with the road surface will not alter.

What's the rolling value of Pi for a wheel and tyre?

/me runs away.

"Tim Lamb" wrote in message
...
In message , Jeff
writes


"The Natural Philosopher" wrote in message
news
On 23/06/18 07:08, Jeff wrote:


"The Natural Philosopher" wrote in message
news https://www.youtube.com/watch?v=_2l5bOhHNxU

Answer. not by very much, if at all.

But the radius clearly does vary significantly.

This seems to be a perpetual urban myth.

It can't be given that Andy and others have had a number
of warnings that have turned out to be accurate every time.


It tyre pressure sensors are using this, it has to be a very very
complicated bit of software to detect - say - less than 1% change in
RPM relative to the other wheels.

Yes, but that isn't hard to measure when its relative to other wheels.

A piece of online research
[https://one.nhtsa.gov/cars/rules/rul...prmonsys.html]
showed that relative wheel rotation was pretty crap at detecting low
tyre pressures especially in all 4 wheels or 2 wheels on the same side
(= I am going round and round in circles!)

Hence the move to in wheel sensors.

I am notr syoing it doesn't work, just that it relies on some pretty
iffy interpreation of very small differences in road speed.

Tyre tread belts do strech under inflation, but not by much. The radius
is completely irrelevant as a road weheel is not, in use, round and
does not have a 'radius.'

Of course it does at the only place that matters, between the axle and
the road.

I've been thinking that but... unless the effective circumference is
changed, the tread in contact with the road surface will not alter. Steel
bracing etc. as mentioned above.

I'm not convinced that it is the circumference that determines
the rotation rate of the wheel. And those who actually measured
it talk about the rolling radius, for a reason and must have done
the most basic tests of watching the rotation rate as the tyre
pressure varies, and see that it does vary by enough to measure.

Maybe there is some perceptible scrubbing going on.

Why should there be any significant scrubbing with say a 20%
lower pressure in the tyre ?

On 23/06/2018 08:59, Tim Lamb wrote:


I've been thinking that but... unless the effective circumference is
changed, the tread in contact with the road surface will not alter.
Steel bracing etc. as mentioned above.

Maybe there is some perceptible scrubbing going on.



Yes but there seems to be a lot of work which supports changes in
dynamic rolling radius separate from slip. Eg this paper reports the
results of modelling it in terms of tread and belt displacement, and
claims the predicted variation of radius with pressure agrees well with
measurements.

https://www.researchgate.net/publication/312641092_A_theoretical_model_for_the_tread_slip_a nd_the_effective_rolling_radius_of_the_tyres_in_fr ee_rolling

Though my gut is more attracted to Andy's "variation in the value of Pi"
thesis: sort of fits with my feeling that BMW drivers come from a
different universe.


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

On 23/06/2018 08:59, Tim Lamb wrote:


I've been thinking that but... unless the effective circumference is
changed, the tread in contact with the road surface will not alter.
Steel bracing etc. as mentioned above.

Maybe there is some perceptible scrubbing going on.


In any rolling contact that is transmitting tangential load there will
be some "slip". Not much, maybe, but some. I could believe that the slip
might vary with inflation pressure and this could be enough for the
brake sensors to detect, given suitably clever logging and processing.

(Ref. Bowden & Tabor Volume 2, can't quote the chapter because I don't
have a copy to hand).

---
This email has been checked for viruses by Avast antivirus software.
https://www.avast.com/antivirus

On 23/06/18 08:09, Jeff wrote:


"The Natural Philosopher" wrote in message
news
On 23/06/18 07:08, Jeff wrote:


"The Natural Philosopher" wrote in message
news https://www.youtube.com/watch?v=_2l5bOhHNxU

Answer. not by very much, if at all.

But the radius clearly does vary significantly.

This seems to be a perpetual urban myth.

It can't be given that Andy and others have had a number
of warnings that have turned out to be accurate every time.


It tyre pressure sensors are using this, it has to be a very very
complicated bit of software to detect - say - less than 1% change in
RPM relative to the other wheels.

Yes, but that isn't hard to measure when its relative to other wheels.

A piece of online research
[https://one.nhtsa.gov/cars/rules/rul...prmonsys.html]
showed that relative wheel rotation was pretty crap at detecting low
tyre pressures especially in all 4 wheels or 2 wheels on the same side
(= I am going round and round in circles!)

Hence the move to in wheel sensors.

I am notr syoing it doesn't work, just that it relies on some pretty
iffy interpreation of very small differences in road speed.

Tyre tread belts do strech under inflation, but not by much. The
radius is completely irrelevant as a road weheel is not, in use, round
and does not have a 'radius.'

Of course it does at the only place that matters, between the axle and
the road.

Oh dear. Oh dear oh dear.

You just dont get it, do you?





--
In a Time of Universal Deceit, Telling the Truth Is a Revolutionary Act.

- George Orwell

"The Natural Philosopher" wrote in message
news
On 23/06/18 08:09, Jeff wrote:


"The Natural Philosopher" wrote in message
news
On 23/06/18 07:08, Jeff wrote:


"The Natural Philosopher" wrote in message
news https://www.youtube.com/watch?v=_2l5bOhHNxU

Answer. not by very much, if at all.

But the radius clearly does vary significantly.

This seems to be a perpetual urban myth.

It can't be given that Andy and others have had a number
of warnings that have turned out to be accurate every time.


It tyre pressure sensors are using this, it has to be a very very
complicated bit of software to detect - say - less than 1% change in
RPM relative to the other wheels.

Yes, but that isn't hard to measure when its relative to other wheels.

A piece of online research
[https://one.nhtsa.gov/cars/rules/rul...prmonsys.html]
showed that relative wheel rotation was pretty crap at detecting low
tyre pressures especially in all 4 wheels or 2 wheels on the same side
(= I am going round and round in circles!)

Hence the move to in wheel sensors.

I am notr syoing it doesn't work, just that it relies on some pretty
iffy interpreation of very small differences in road speed.

Tyre tread belts do strech under inflation, but not by much. The radius
is completely irrelevant as a road weheel is not, in use, round and does
not have a 'radius.'

Of course it does at the only place that matters, between the axle and
the road.

Oh dear. Oh dear oh dear.

You just dont get it, do you?

It is you that doesnt. That distance is the only thing that matters,
it is what determines the rotation rate of the wheel, exactly the
same way the diameter of the wheel determines the rotation
rate of the wheel, but in this case that radius clearly does vary
with the pressure in the tyre. What happens with the rest of
the tyre is completely irrelevant.

On 23/06/2018 07:41, The Natural Philosopher wrote:
On 23/06/18 07:08, Jeff wrote:


"The Natural Philosopher" wrote in message
news
https://www.youtube.com/watch?v=_2l5bOhHNxU

Answer. not by very much, if at all.

But the radius clearly does vary significantly.

This seems to be a perpetual urban myth.

It can't be given that Andy and others have had a number
of warnings that have turned out to be accurate every time.


It tyre pressure sensors are using this, it has to be a very very
complicated bit of software to detect - say - less than 1% change in
RPM relative to the other wheels.

Yes, but that isn't hard to measure when its relative to other wheels.

A piece of online research
[https://one.nhtsa.gov/cars/rules/rul...prmonsys.html]
showed that relative wheel rotation was pretty crap at detecting low
tyre pressures especially in all 4 wheels or 2 wheels on the same side
(= I am going round and round in circles!)

That ruling in 2001 was in the context of what could and couldn't meet a
statutory requirement in the USA for pressure monitoring in new cars
that also alerted if more than one tyre - including all 4 tyres equally
- are 25% or more below pressure. It's no surprise that indirect
methods couldn't meet that requirement.

Hence the move to in wheel sensors.


OTOH https://en.wikipedia.org/wiki/Tire-p...itoring_system has

"Since factory installation of TPMS became mandatory in November 2014
for all new passenger vehicles in the EU, various iTPMS [that "i"'s for
indirect] have been type-approved according to UN Regulation R64.
Examples for this are most of the VW group models, but also numerous
Volvo, Opel, Ford, Mazda, PSA, FIAT and Renault models. iTPMS are
quickly gaining market shares in the EU and are expected to become the
dominating TPMS technology in the near future.

iTPMS are regarded as inaccurate by some due to their nature, but given
that simple ambient temperature variations can lead to pressure
variations of the same magnitude as the legal detection thresholds, many
vehicle manufacturers and customers value the ease of use and tire/wheel
change higher than the theoretical accuracy of dTPMS."

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

On 23/06/2018 08:44, Robin wrote:

That ruling in 2001 was in the context of what could and couldn't meet a
statutory requirement in the USA for pressure monitoring in new cars
that also alerted if more than one tyre - including all 4 tyres equally
- are 25% or more below pressure.Â* It's no surprise that indirect
methods couldn't meet that requirement.

If the car has sat nav installed and available to the car's computer, as
many do now, the speed across the ground could be compared to the wheel
rotation. That could detect all 4 wheels being equally underinflated.
But, that's 2018, not 2001.

GB wrote
Robin wrote

That ruling in 2001 was in the context of what could and couldn't meet a
statutory requirement in the USA for pressure monitoring in new cars that
also alerted if more than one tyre - including all 4 tyres equally - are
25% or more below pressure. It's no surprise that indirect methods
couldn't meet that requirement.

If the car has sat nav installed and available to the car's computer, as
many do now, the speed across the ground could be compared to the wheel
rotation. That could detect all 4 wheels being equally underinflated.

Maybe. gps speed isnt that accurate in the short distances.

And if you get 4 new tyres at a time, as many do, and the tyre place
underinflates all of them by the same amount, and the tyres are a
bit different profile wise to the previous set, its going to be hard
for the system to work out that they are all underinflated. And thats
the main situation where all 4 would be equally under inflated.

But, that's 2018, not 2001.

On 23/06/2018 07:41, The Natural Philosopher wrote:


I am notr syoing it doesn't work, just that it relies on some pretty
iffy interpreation of very small differences in road speed.


It seems to work fine on my Audi. It tells me if there is a problem with
a single tyre or to check all tyres. It detects tyre pressures which are
different to what was saved, you need to tell the car the tyres are at
the correct pressures.

I've seen it detect something is wrong with all tyres. This was after
rotating the tyres front to back and failing to reset the pressures
monitor. The fronts are run at 38-40PSI and the rears at 32-34PSI. It
chimed after about 1/2mile that I should check all 4 tyres.

It detects rotational rate not expected due to pressure change, either
under or over inflation. I had a persistent slow. It turns out the
alloy's painted surface where the bead meets the wheel was corroded and
leaking. My local tyre place cleaned and painted this and the tyre was
fine since. However, they pumped up the tyre hard during checking and
didn't set the correct pressure. About 2miles after driving the check
tyre chime went off. The screen said check pressure and it shows a flat
tyre but it was over inflated in this case. The system detected it was
rotating at the wrong rate for what was set. It doesn't have an over
inflated graphic!

A pressure sender would give an instant out of range indication but this
system has never failed to warn me of issues I'd not notice from driving
immediately.

"Chris Hogg" wrote in message
...
On Sat, 23 Jun 2018 16:08:44 +1000, "Jeff" wrote:



"The Natural Philosopher" wrote in message
news
https://www.youtube.com/watch?v=_2l5bOhHNxU

Answer. not by very much, if at all.

But the radius clearly does vary significantly.

Does it?

It clearly does with the distance between the axle and the ground.

The perimeter certainly changes shape from being
near-circular to having a significant flat side against the ground,
but if the radius changed significantly, that would also mean a
circumference change,

No it does not. What happens is that the distance between
the rim and the outer flat surface of the tyre changes a lot.
That is very clearly visible with a flat tyre still on the car.

and the read-outs from the various gauges such
as speedometer and odometer would no longer be accurate.

That inaccuracy wouldn't be noticed even if it was
done from the wheel which has the flat tyre.

There are
also steel reinforcing belts beneath the tread that would have to
stretch if the circumference increased.

But the circumference does not increase when the radius where
the wheel touches the ground reduces significantly and visibly.

"Jeff" Wrote in message:


"Chris Hogg" wrote in message
...
On Sat, 23 Jun 2018 16:08:44 +1000, "Jeff" wrote:



"The Natural Philosopher" wrote in message
news https://www.youtube.com/watch?v=_2l5bOhHNxU

Answer. not by very much, if at all.

But the radius clearly does vary significantly.

Does it?

It clearly does with the distance between the axle and the ground.

The perimeter certainly changes shape from being
near-circular to having a significant flat side against the ground,
but if the radius changed significantly, that would also mean a
circumference change,

No it does not. What happens is that the distance between
the rim and the outer flat surface of the tyre changes a lot.
That is very clearly visible with a flat tyre still on the car.

and the read-outs from the various gauges such
as speedometer and odometer would no longer be accurate.

That inaccuracy wouldn't be noticed even if it was
done from the wheel which has the flat tyre.

There are
also steel reinforcing belts beneath the tread that would have to
stretch if the circumference increased.

But the circumference does not increase when the radius where
the wheel touches the ground reduces significantly and visibly.



Hi woddles!
--
--
Jim K


----Android NewsGroup Reader----
http://usenet.sinaapp.com/

On 23/06/18 13:42, Chris Hogg wrote:
On Sat, 23 Jun 2018 17:04:38 +1000, "Jeff" wrote:



"Chris Hogg" wrote in message
...
On Sat, 23 Jun 2018 16:08:44 +1000, "Jeff" wrote:



"The Natural Philosopher" wrote in message
news https://www.youtube.com/watch?v=_2l5bOhHNxU

Answer. not by very much, if at all.

But the radius clearly does vary significantly.

Does it?

It clearly does with the distance between the axle and the ground.

I think we're at cross-purposes here. Obviously, as you say, when a
tyre is flat, the axle is nearer the ground. But is it reasonable to
regard that as the radius of the tyre?

Not if you have any understanding of mechanics. The whole tread, up to
and including a caterpillar track, goes round once per revolution of the
track or tyre.

THAT is what determines the RPM/speed relations ship.

What happens with tyre pressures is quite clear. The tread stretches
slightly under higher pressures. How much will be a function of the tyre
construction. And this is what the sensors rely on.

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.

For it to be any other way the tyre must slip on the rim or on the road,
substantially.




--
"I am inclined to tell the truth and dislike people who lie consistently.
This makes me unfit for the company of people of a Left persuasion, and
all women"

On 23/06/18 17:01, The Natural Philosopher wrote:
On 23/06/18 13:42, Chris Hogg wrote:
On Sat, 23 Jun 2018 17:04:38 +1000, "Jeff" wrote:



"Chris Hogg" wrote in message
...
On Sat, 23 Jun 2018 16:08:44 +1000, "Jeff" wrote:



"The Natural Philosopher" wrote in message
news https://www.youtube.com/watch?v=_2l5bOhHNxU

Answer. not by very much, if at all.

But the radius clearly does vary significantly.

Does it?

It clearly does with the distance between the axle and the ground.

I think we're at cross-purposes here. Obviously, as you say, when a
tyre is flat, the axle is nearer the ground. But is it reasonable to
regard that as the radius of the tyre?

Not if you have any understanding of mechanics.Â* The whole tread, up to
and including a caterpillar track, goes round once per revolution of the
track or tyre.

THAT is what determines the RPM/speed relations ship.

A revolution is the movement of one object (*point* on circumference)
around a centre (hub).
Your caterpillar track is supported by wheels, each of which will do
many revolutions for one revolution of the track. The circumference of
the track is many times the circumference of each wheel.


What happens with tyre pressures is quite clear. The tread stretches
slightly under higher pressures. How much will be a function of the tyre
construction. And this is what the sensors rely on.

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.


For it to be any other way the tyre must slip on the rim or on the road,
substantially.

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.

Go and get a technical education




--
"It is an established fact to 97% confidence limits that left wing
conspirators see right wing conspiracies everywhere"

"pamela" wrote in message
...
On 17:01 23 Jun 2018, The Natural Philosopher wrote:

On 23/06/18 13:42, Chris Hogg wrote:
On Sat, 23 Jun 2018 17:04:38 +1000, "Jeff"
wrote:



"Chris Hogg" wrote in message
...
On Sat, 23 Jun 2018 16:08:44 +1000, "Jeff"
wrote:



"The Natural Philosopher" wrote in
message news https://www.youtube.com/watch?v=_2l5bOhHNxU

Answer. not by very much, if at all.

But the radius clearly does vary significantly.

Does it?

It clearly does with the distance between the axle and the
ground.

I think we're at cross-purposes here. Obviously, as you say, when
a tyre is flat, the axle is nearer the ground. But is it
reasonable to regard that as the radius of the tyre?

Not if you have any understanding of mechanics. The whole tread,
up to and including a caterpillar track, goes round once per
revolution of the track or tyre.

Surely the circumference changes because the area in contact with the
road is a chord and not an arc.

Nope, not when the circumference doesn’t stretch and it doesn’t
with steel belted radials.

The length of the chord increases when the tyre is underinflated on
account of compression of more of the former arc in contact with the
road. The circumference is reduced.

Not with steel belted radials.

Only if all the compression of the former arc occurs at the leading
edge of contact would the speed be unaffected.

The circumference is irrelevant. What determines the rotation
rate of the wheel is the distance between the axle and the road.

THAT is what determines the RPM/speed relations ship.

What happens with tyre pressures is quite clear. The tread
stretches slightly under higher pressures. How much will be a
function of the tyre construction. And this is what the sensors
rely on.

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

For it to be any other way the tyre must slip on the rim or on the
road, substantially.

On Sun, 24 Jun 2018 07:12:45 +1000, cantankerous geezer Rot Speed blabbered,
again:


Not if you have any understanding of mechanics. The whole tread,
up to and including a caterpillar track, goes round once per
revolution of the track or tyre.

Surely the circumference changes because the area in contact with the
road is a chord and not an arc.

Nope,

I KNEW it! LMAO

--
Sqwertz to Rot Speed:
"This is just a hunch, but I'm betting you're kinda an argumentative
asshole.
MID:

"Chris Hogg" wrote in message
news
On Sat, 23 Jun 2018 17:04:38 +1000, "Jeff" wrote:



"Chris Hogg" wrote in message
. ..
On Sat, 23 Jun 2018 16:08:44 +1000, "Jeff" wrote:



"The Natural Philosopher" wrote in message
news https://www.youtube.com/watch?v=_2l5bOhHNxU

Answer. not by very much, if at all.

But the radius clearly does vary significantly.

Does it?

It clearly does with the distance between the axle and the ground.

I think we're at cross-purposes here. Obviously, as you say, when a
tyre is flat, the axle is nearer the ground. But is it reasonable to
regard that as the radius of the tyre?

It is the only distance that matters with the rotation speed of the wheel.
The distance between the axle and the top of the tyre is irrelevant to that.

If you simplify the shape and
call it an ellipse, then you have two radii; quite how many radii
would be needed to describe a tyre with a flat on one side, I wouldn't
like to speculate.

But those distances are irrelevant to the rotation speed of the wheel.

But the circumference, perhaps perimeter would be a
better word, won't have changed significantly. It'll just become
distorted, i.e. no longer circular.

Yes, but that isnt what determines the rotation rate of the wheel.

But that assumes there is a weight pressing down on the tyre, which I
grant you, would be the case for a loaded tyre on a vehicle. But I was
thinking of an unloaded tyre;

Its irrelevant when deciding if the tyre is under inflated.

does the circumference change between
under-inflated and fully- or even over-inflated?

Not by much at all with steel belted radials and any system
that detects under inflated tyres has to work with those.

When I were a lad in
the days when tyres had inner tubes, we used to go to our local garage
and get old tubes that were no longer serviceable, patch them where
necessary, inflate then and use them as super-sized rubber rings for
taking down to the beach (and probably getting blown out to sea!). As
they were inflated, the radius and circumference most certainly did
increase; they blew up like a balloon. But put them into a tyre and
there'd be no significant change in the circumference as they inflated
and deflated. The structure of the tyre wouldn't allow that to happen.

Likewise, I suggest that the circumference (perimeter if you prefer)
of a modern tubeless tyre doesn't change significantly as it inflates
or deflates.

Yes, but the circumference isnt what determines the rotation
rate of the tyre on a moving car.

Every full rotation of the hub must correspond to a full rotation of
the perimeter, regardless of the state of inflation of the tyre,
otherwise serious slippage will be occurring between the tyre and the
rim, which would result in friction heating and fairly rapid failure.

Yes, but the circumference doesn't determine the rotation rate of the tyre.

So as far as speedometers and odometers are concerned, state of
inflation won't make a significant difference.

That's arguable with the very small variations being discussed.

(What amounts to 'significant' as I've used it here, I'm not sure; it
depends on the pressure difference being considered between under and
fully inflated, and the elasticity of the structures within the
treaded surface of the tyre, amongst other things, but others in this
thread have mentioned figures of around 1% for the stretching of the
perimeter as the tyre is inflated. In this context, I would regard
that as not significant).

But someone must have checked that the ABS rotation rate does change
with under inflated tyres otherwise that wouldn't be used to detect
under inflated tyres.

On Sat, 23 Jun 2018 07:29:26 +0100, Chris Hogg wrote:

On Sat, 23 Jun 2018 16:08:44 +1000, "Jeff" wrote:



"The Natural Philosopher" wrote in message
news
https://www.youtube.com/watch?v=_2l5bOhHNxU

Answer. not by very much, if at all.

But the radius clearly does vary significantly.

Does it? The perimeter certainly changes shape from being
near-circular to having a significant flat side against the ground,
but if the radius changed significantly, that would also mean a
circumference change, and the read-outs from the various gauges such
as speedometer and odometer would no longer be accurate. There are
also steel reinforcing belts beneath the tread that would have to
stretch if the circumference increased.

My limited experience isn't with car tyres.
Now, the circumference doesn't have to change, only the effective rolling
circumference (see down-thread). (An ellipse, if not too far from circular,
has v. liitle change of circumference, IIRC, so view a softish tyre as a
one-sided ellipse and there's even less change).To me, the rolling
circumference is simply that which is calculated from the 'radius' at the
point under load, so if the axle is 10% lower the rolling circumference is
10% less.

On my bikes I measured rolling circumference (it's difficult to measure
radius to the ground of a loaded tyre as being sure that the bike is at 90
deg. to ground whilst loading the bars...
For example figures only, a 5-bar tyre might be 212 cm unladen and about 210
- 211 with ~30 kg on the bars.
A 6.5 - 7-bar tyre showed no measurable difference.
I haven't measured lower pressure tyres.

The difference at 5 bar is =1% but, as I logged my mileages, 1% on 20k
miles...
As for up on the pedals or sitting down on a 20% hill, too difficult to be
bothered!
--
Peter.
The gods will stay away
whilst religions hold sway

In article ,
PeterC wrote:
My limited experience isn't with car tyres. Now, the circumference
doesn't have to change, only the effective rolling circumference (see
down-thread). (An ellipse, if not too far from circular, has v. liitle
change of circumference, IIRC, so view a softish tyre as a one-sided
ellipse and there's even less change).To me, the rolling circumference
is simply that which is calculated from the 'radius' at the point under
load, so if the axle is 10% lower the rolling circumference is 10% less.

Yes. You are effectively making a triangle with the base being the flat
part of the tyre. And that base is going to be a shorter length than a
similar triangle where that base is a curve.

In other words, the radius at the point of contact to the road determines
the gearing. Whatever happens to the rest of the tyre is immaterial.

--
*A cartoonist was found dead in his home. Details are sketchy.*

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

On 23/06/2018 06:56, The Natural Philosopher wrote:
https://www.youtube.com/watch?v=_2l5bOhHNxU

Answer. not by very much, if at all.

This seems to be a perpetual urban myth.

It tyre pressure sensors are using this, it has to be a very very
complicated bit of software to detect - say - less than 1% change in RPM
relative to the other wheels.



I wasn't impressed by a bloke pushing a van who shows no signs of
understanding the meaning of "resolution". OTOH put "tyre rolling
radius pressure" in a well-known search engine[1] and the first hit is
a paper from University Politechnica of Bucharest giving the variation
in rolling radius for a range of pressures and speeds on a dynamometer[2].


Includes:

"When the inflation pressure is changed by ± 30 % with respect to the
nominal value, the increase of dynamic rolling radius has relative
values ranging between 0.88 % and 0.95 %, therefore close to 1 %.
It can be asserted that, for all the considered values of rolling speed,
the inflation pressure has an important influence on the tyre dynamic
rolling radius."




[1] I looked for it after reading the thread in u.r.c.maintenance about
pressure monitors, not in response to your "fake myth"

[2] G Anghelache and R Moisescu 2017 IOP Conf. Ser.: Mater. Sci. Eng.
252 012014

iopscience.iop.org/article/10.1088/1757-899X/252/1/012014/pdf

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

On 23/06/18 07:31, Robin wrote:
On 23/06/2018 06:56, The Natural Philosopher wrote:
https://www.youtube.com/watch?v=_2l5bOhHNxU

Answer. not by very much, if at all.

This seems to be a perpetual urban myth.

It tyre pressure sensors are using this, it has to be a very very
complicated bit of software to detect - say - less than 1% change in
RPM relative to the other wheels.



I wasn't impressed by a bloke pushing a van who shows no signs of
understanding the meaning of "resolution".Â* OTOH put "tyre rolling
radiusÂ* pressure" in a well-known search engine[1] and the first hit is
a paper from University Politechnica of Bucharest giving the variation
in rolling radius for a range of pressures and speeds on a dynamometer[2].


Includes:

"When the inflation pressure is changed by ± 30 % with respect to the
nominal value, the increase of dynamic rolling radius has relative
values ranging between 0.88 % and 0.95 %, therefore close to 1 %.
It can be asserted that, for all the considered values of rolling speed,
the inflation pressure has an important influence on the tyre dynamic
rolling radius."


Well that is what I said.

Around 1% *at best* circumference change, Though why they have to call
it a 'dynamic rolling radius' is beyond me. There is no such thing as a
constant radius on a tyre. It isn't round.

1% will be totally swamped by wheelspin, slip under traction or bråking
or cornering itself.

If you are lucky in a straight bit of road it might spot a wheel 30%
underinflated. Not two though.

But I can tell if a wheel is 10% underinflated by the way the car handles




[1] I looked for it after reading the thread in u.r.c.maintenance about
pressure monitors, not in response to your "fake myth"


In fact your data supports my position. And the video. There is bugger
all (1%) change in circumference with +- 30% pressure.

That this may just be enough with sophistcated sofwtare to light a
warning light on a cheap car when one tyre is so flat only the most
totally crap driver hasn't spotted it, is a tribute to modern software,
not a foregone comnclusions from a 'change in radius'


[2] G Anghelache and R Moisescu 2017 IOP Conf. Ser.: Mater. Sci. Eng.
252 012014

iopscience.iop.org/article/10.1088/1757-899X/252/1/012014/pdf



--
€œIt is hard to imagine a more stupid decision or more dangerous way of
making decisions than by putting those decisions in the hands of people
who pay no price for being wrong.€�

Thomas Sowell

"The Natural Philosopher" wrote in message
news
On 23/06/18 07:31, Robin wrote:
On 23/06/2018 06:56, The Natural Philosopher wrote:
https://www.youtube.com/watch?v=_2l5bOhHNxU

Answer. not by very much, if at all.

This seems to be a perpetual urban myth.

It tyre pressure sensors are using this, it has to be a very very
complicated bit of software to detect - say - less than 1% change in RPM
relative to the other wheels.



I wasn't impressed by a bloke pushing a van who shows no signs of
understanding the meaning of "resolution". OTOH put "tyre rolling radius
pressure" in a well-known search engine[1] and the first hit is a paper
from University Politechnica of Bucharest giving the variation in rolling
radius for a range of pressures and speeds on a dynamometer[2].


Includes:

"When the inflation pressure is changed by ± 30 % with respect to the
nominal value, the increase of dynamic rolling radius has relative values
ranging between 0.88 % and 0.95 %, therefore close to 1 %.
It can be asserted that, for all the considered values of rolling speed,
the inflation pressure has an important influence on the tyre dynamic
rolling radius."


Well that is what I said.

Around 1% *at best* circumference change, Though why they have to call it
a 'dynamic rolling radius' is beyond me.

Because that is the distance that matters.

There is no such thing as a
constant radius on a tyre. It isn't round.

They dont say it is constant around the wheel. The radius at other than
where the tyre is on the road is irrelavant and clearly visibly different to
where the tyre is on the road.

1% will be totally swamped by wheelspin, slip under traction or bråking or
cornering itself.

But when the rotation rate is ignored in those situations it is still
possible to detect a flat tyre when it is observed that the rate of
rotation of that wheel is different to the others.

If you are lucky in a straight bit of road it might spot a wheel 30%
underinflated. Not two though.

But it isnt two, it is one out of four.

But I can tell if a wheel is 10% underinflated by the way the car handles

But not all drivers can do that.



[1] I looked for it after reading the thread in u.r.c.maintenance about
pressure monitors, not in response to your "fake myth"


In fact your data supports my position. And the video. There is bugger all
(1%) change in circumference with +- 30% pressure.

That this may just be enough with sophistcated sofwtare to light a warning
light on a cheap car when one tyre is so flat only the most totally crap
driver hasn't spotted it, is a tribute to modern software, not a foregone
comnclusions from a 'change in radius'

And yet Andy has seen it do a lot better than that.

[2] G Anghelache and R Moisescu 2017 IOP Conf. Ser.: Mater. Sci. Eng. 252
012014

iopscience.iop.org/article/10.1088/1757-899X/252/1/012014/pdf

On 23/06/18 08:17, Jeff wrote:
That this may just be enough with sophistcated sofwtare to light a
warning lightÂ* on a cheap car when one tyre is so flat only the most
totally crap driver hasn't spotted it, is a tribute to modern
software, not a foregone comnclusions from a 'change in radius'

And yet Andy has seen it do a lot better than that.

No, That is pretty much wot he said


--
"Socialist governments traditionally do make a financial mess. They
always run out of other people's money. It's quite a characteristic of them"

Margaret Thatcher

Robin quoted:

"When the inflation pressure is changed by ± 30 % with respect to the
nominal value, the increase of dynamic rolling radius has relative
values ranging between 0.88 % and 0.95 %, therefore close to 1 %."

A car with e.g. 35R18 tyres/wheels progresses just under 2m per
revolution, with the ABS sensor receiving e.g. 48 pulses per revolution,
at 30mph that's about 320Hz.

Even if the distance travelled per revolution is reduced by just 1% due
to low pressure, a shift on one wheel of +3Hz wouldn't be hard to
detect, especially when it has other clues such as steering wheel angle
sensor so it knows when the differential(s) is/are doing their thing in
a corner.

The Natural Philosopher wrote:

https://www.youtube.com/watch?v=_2l5bOhHNxU
Answer. not by very much, if at all

looked to be half the width of a piece of insulating tape per
revolution, what was even the point of only measuring the rolling
distance once?

This seems to be a perpetual urban myth.
It tyre pressure sensors are using this

And iTPMS systems *are* using it

it has to be a very very
complicated bit of software to detect - say - less than 1% change in RPM
relative to the other wheels.

Little extra complication within the ABS unit, how many pulses per
revolution does it process from an ABS reluctor ring? 40 to 60 "teeth"
seems common. If the ABS unit can detect wheel slowing (i.e. a skid
starting) then it can detect a wheel speeding up (e.g. from a puncture)

Nobody is suggesting it decides if it's a puncture within a single
revolution, it detects over a period of time, 1% isn't that tiny.

I noticed the actual TPMS trigger often tended to be when you put your
foot down going round a corner/roundabout.

On Sat, 23 Jun 2018 07:38:15 +0100, Andy Burns
wrote:

The Natural Philosopher wrote:

https://www.youtube.com/watch?v=_2l5bOhHNxU
Answer. not by very much, if at all

looked to be half the width of a piece of insulating tape per
revolution, what was even the point of only measuring the rolling
distance once?

This seems to be a perpetual urban myth.
It tyre pressure sensors are using this

And iTPMS systems *are* using it

snip

The problem with Turnip is that he is a left brainer and once he can't
comprehend something, it must be wrong or simply can't happen and he
will find other (bogus of course) examples to try to support his case.
;-)

It's *obvious* such things work because they just do ... and the fact
that he can't understand how or why, doesn't stop that from being a
fact! ;-)

If you want to calculate the rpm of a wheel at a particular mph you
use the 'effective rolling radius' to do so, not the nominal
circumference of the tyre (with conventional tyres [1]).

https://www.tut.fi/ms/muo/vert/11_ty...ing_radius.htm

I did this when designing an electronic speedometer for the electric
racing motorbike I built.

I measured the 'rolling radius' with the tyre at the optimum (high)
pressure and with all the normal loads on the bike (me, batteries,
fairing's etc). I then used that to determine the rpm/mph and used a f
to V converter to take my rotational sensor output and feed it to a
DVM, calibrated to represent the mph (all done on the bench using an
oscillator and DVM). On the track a RADAR gun determined I was doing
37mph and my display said I was doing 37.4. ;-)

At no time did I measure or use the circumference of the wheel
directly. ;-)

Cheers, T i m

[1] With dragsters the driven tyres expand quite a lot to effectively
increase the gearing speed. ;-)

Not looked at this, but seeing as an over inflated tyre is not as grippy as
the designed inflation and also given that hot air adds pressure I have also
often wondered about the detection. Of course a couple of ideas do come to
mind. Monitor the tyres and compare them. If one is not behaving like the
rest then something is definitely not right.
The other thought is that if the car is still and one tyre is changing, say
over night, then you got a leak in that tyre. Its not so much a pressure
sensor issue, but a comparison one.
Brian

--
----- --
This newsgroup posting comes to you directly from...
The Sofa of Brian Gaff...

Blind user, so no pictures please
Note this Signature is meaningless.!
"The Natural Philosopher" wrote in message
news
https://www.youtube.com/watch?v=_2l5bOhHNxU

Answer. not by very much, if at all.

This seems to be a perpetual urban myth.

It tyre pressure sensors are using this, it has to be a very very
complicated bit of software to detect - say - less than 1% change in RPM
relative to the other wheels.


--
"When one man dies it's a tragedy. When thousands die it's statistics."

Josef Stalin

Apologies to Lonnie Donegan.
:-)
Brian

--
----- --
This newsgroup posting comes to you directly from...
The Sofa of Brian Gaff...

Blind user, so no pictures please
Note this Signature is meaningless.!
"Brian Gaff" wrote in message
news
Not looked at this, but seeing as an over inflated tyre is not as grippy
as the designed inflation and also given that hot air adds pressure I have
also often wondered about the detection. Of course a couple of ideas do
come to mind. Monitor the tyres and compare them. If one is not behaving
like the rest then something is definitely not right.
The other thought is that if the car is still and one tyre is changing,
say over night, then you got a leak in that tyre. Its not so much a
pressure sensor issue, but a comparison one.
Brian

--
----- --
This newsgroup posting comes to you directly from...
The Sofa of Brian Gaff...

Blind user, so no pictures please
Note this Signature is meaningless.!
"The Natural Philosopher" wrote in message
news
https://www.youtube.com/watch?v=_2l5bOhHNxU

Answer. not by very much, if at all.

This seems to be a perpetual urban myth.

It tyre pressure sensors are using this, it has to be a very very
complicated bit of software to detect - say - less than 1% change in RPM
relative to the other wheels.


--
"When one man dies it's a tragedy. When thousands die it's statistics."

Josef Stalin

In article ,
The Natural Philosopher wrote:
https://www.youtube.com/watch?v=_2l5bOhHNxU

Answer. not by very much, if at all.

This seems to be a perpetual urban myth.

It tyre pressure sensors are using this, it has to be a very very
complicated bit of software to detect - say - less than 1% change in RPM
relative to the other wheels.

You must be in the sales side of speedometers if you think a 1% change
difficult to detect these days.

--
*They told me I had type-A blood, but it was a Type-O.*

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

On 23/06/2018 06:56, The Natural Philosopher wrote:

https://www.youtube.com/watch?v=_2l5bOhHNxU

Answer. not by very much, if at all.

So the short answer to your question is "yes".

This seems to be a perpetual urban myth.

Which you have just agreed with by claiming there is a small change.

It tyre pressure sensors are using this, it has to be a very very
complicated bit of software to detect - say - less than 1% change in RPM
relative to the other wheels.

Can't see that being too difficult in itself - especially as you
probably have input from other sensors and know the steering angle input
and so can assess when you are driving straight and not under high
acceleration etc.

Type pressure monitoring will need to be more sensitive to rate of
change than absolute difference since unequal tyre wear would otherwise
be flagged.


--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

On 23/06/18 14:28, John Rumm wrote:
On 23/06/2018 06:56, The Natural Philosopher wrote:

https://www.youtube.com/watch?v=_2l5bOhHNxU

Answer. not by very much, if at all.

So the short answer to your question is "yes".

This seems to be a perpetual urban myth.

Which you have just agreed with by claiming there is a small change.

No the urban myth says that since there is say a 10% change in what
peooplle think is 'the radius', therefore the RPM will be 10% slower.


It tyre pressure sensors are using this, it has to be a very very
complicated bit of software to detect - say - less than 1% change in
RPM relative to the other wheels.

Can't see that being too difficult in itself - especially as you
probably have input from other sensors and know the steering angle input
Â*and so can assess when you are driving straight and not under high
acceleration etc.


Why would there be monitors on steering angle?


Type pressure monitoring will need to be more sensitive to rate of
change than absolute difference since unequal tyre wear would otherwise
be flagged.


Well teh way it aseems to work is that one wheel will overotate with
respect to its diagonal consisetntly.

But not by very much.




--
Its easier to fool people than to convince them that they have been fooled.
Mark Twain

The Natural Philosopher wrote:

Why would there be monitors on steering angle?

For the stability control system.

But once they're a standard part of the car you can use feed the data to
other systems, such as overlaying the curves on the reversing camera
display, or knowing when you're travelling straight and therefore the
TPMS doesn't have to worry about different wheel speeds caused by the
action of a differential.

On 23/06/18 17:13, Andy Burns wrote:
The Natural Philosopher wrote:

Why would there be monitors on steering angle?

For the stability control system.

But once they're a standard part of the car you can use feed the data to
other systems, such as overlaying the curves on the reversing camera
display, or knowing when you're travelling straight and therefore the
TPMS doesn't have to worry about different wheel speeds caused by the
action of a differential.

All to modern for me. Never seen steering angle sensed yet on any car
I've driven.


--
€œProgress is precisely that which rules and regulations did not foresee,€�

€“ Ludwig von Mises

The Natural Philosopher wrote:

Andy Burns wrote:

The Natural Philosopher wrote:

Why would there be monitors on steering angle?

For the stability control system.

All to modern for me.

It's because there are so many inputs available to the electronics,
wheel speeds, steering angle, yaw rate, accelerometer(s), that figuring
out a flat tyre has just become another part of TCB to the ABS unit.

Never seen steering angle sensed yet on any car I've driven.

I thought you have/had a Disco?
Surprising if such a relatively high centre of mass vehicle didn't have
stability control (or whatever LR call it)