"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.