On 25/06/18 06:50, Jeff wrote:


"Tjoepstil" wrote in message
news
On 24/06/18 22:18, Jeff wrote:
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, you don't.

Yes you do, as you should be able to see with a rim with no tyre at all.
As the rim diameter changes, the rotation rate will obviously change.

Thats becausd in that case the wehel is in fact round. Ther is a perfect
relatinship between circumgerencve and radious


Once iuy has a non round tyre on, your assumptions are invalid.


a tyre and wheel is not a sun and planet reduction gear,

It is a rack and pinion tho.

the tyre is not
rotating relative to the wheel,

Correct.

ergo every revolution of the wheel one
circumference of tyre must move along the road.

Yes, but it is the distance between the axle and the road
that determines the rotation rate.

No it isn't.

it is NOT a sun and planet gear. It is a squashy tyre on a wheel

https://www.youtube.com/watch?v=XNy4sdDJg2o

Look at the video 8:45 in and see what YOU are describing happening.


If you think thats how a flat tyre behaves god help you.


The ABS sensors do not detectÂ* a massive change in radius, but a small
change in circumference due to the tread shrinking very slightly.

They actually detect the substantial change in the rotation rate
the is due to the substantial change in the distance between the
axle and the road.

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

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



--
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