"T i m" wrote in message
...
On Fri, 29 Jun 2018 10:00:30 +1000, "Jeff" wrote:



"T i m" wrote in message
. ..
On Fri, 29 Jun 2018 06:43:35 +1000, "Jeff" wrote:



"T i m" wrote in message
m...

Bingo.

I was walking round the park with our daughter earlier and I gave her
the nutshell iTPMS overview and asked her how she thought it might
work ... how the circumference could become shorter for the iTPMS to
'sense' the increased RPM.

"As the tyre gets flatter it spreads more and that makes the
circumference shorter and so the revs higher?"

Not convinced and that summary makes no sense either.

Then come up with a more credible one?

I prefer to measure, not speculate.

Come up with the measurements then?

As I said, not possible, because while my car has ABS,
the wheel rotation rate of the individual wheels isnt
displayed on the OBD2 data.

the tyre 'spread more' as it gets flatter and why would the
circumference
get shorter even if it did

What part of 'pantographing' don't you get OOI?

I've never been convinced by your pantograph line.

It's not mine, it's what those people who know know.

The steel belts arent panto graphs.

Ok. The belts are woven between the beads in a ziz-zag, working their
way round the tyre till they join up again. these cross at roughly 90
degrees and form a parallelogram.

But they arent joined where they cross like those pop rivet setters.

When you load a tyre that causes it
to widen, it has to get the material from somewhere and because the
rubber is 'bound' to some degree by the bets, the only way that can
happen is some foreshortening of the length of the tread from where
it's distorted.

Never been convinced about that either. Yes, when the tyre pressure
is reduced a bit, there is more tyre in contact with the road, and the
walls clearly bulge more, but there isnt any evidence that there is
more tyre in contact with the road across the tyre itself.

What do you have as an alternative explanation?

As I said, I prefer to measure and then, when that measurement does
show that the wheel rotation rate does vary with the circumference
and not with the distance between the axle and the road, look for
an explanation of why it happens like that.

Have you ever seen one of those expanding pop rivet guns ... of the
joke boxing glove on an expanding arm?

When those things get wider they get shorter.

Yes, but the steel belts in car tyres are nothing like that.

They are everything like that (but maybe you just don't realise it)?

There is no pivot at each crossing point like there is with the pop rivet
setter

Imagine one bent round into a circle (like the internal structure of a
tyre). What would you get if it was made out of flexible materials at
the flat section at the bottom, where the thing spreads out?

I really can't think of any other way to make it any simpler for you?

Trouble is that it nothing like a real steel belt in a car tyre and is
encased in rubber too.