On 27/06/18 19:36, Tim Streater wrote:
You can also imagine that if you could get hold of a tire of the same
overall diameter but to go on a much smaller wheel, that the spiralling
effect when flat would be much more pronounced as the tire wall would
be bigger. But, once spiralled up, one turn

I've been thinking about this a lot trying to make it simple enough for
even a remoaner to understand.

The fallacy is in Huge's basic premise that because the axle is a given
height above te ground, that represents the 'effective/rolling radius*'
of the tyre.

It does not.

The 'effective/rolling radius' is /always/ the circumference divided by
2 PI.

How can this be? Quite simply because the tyre is attached to the wheel
all round, and the tyre is dragged along by the sidewall such that the
tread is moving faster (angular velocity) than the rim at the point of
'flatness'.

So Huge's assumption that the tyre tread speed is actually it's distance
from the axis of rotation, times the speed of rotation of the wheel, is
simply a mistake. It is in fact *greater*, at that point, and its the
sidewall flexure that takes up the strain, and the attachment of the
tyre at other points of the rim that creates that strain.

Should the wheel deflate completely, then the strain in the sidewall and
the friction between the tread and the rim as the two models
compete...leads to rapid separation of tread and wheel.

You then end up then with a wheel rim and tyre tread rotating at
completely different angular velocity. The triumph of 'Huge's model' is
to rip the tyre sidewall apart to allow that to happen.


If you follow F1 you can see this regularly - you end up with the
sidewall disintegrating and a more or less intact tread separating from
the car wheel entirely.


This leads to the conclusions that what affects wheel RPM - in a non
slip case - apart from car speed, is change in *circumference* alone,
and that will be a function of tyre tread elasticity, tyre pressure and
tyre RPM only, due to 'centrifugal force'.

Loading won't affect it at all.

And whoever dreamt up 'effective' or 'rolling' radius deserves to be
strapped to a centrifuge.

A little knowledge is a dangerous thing.

So is relying on 'experts' who are equally ignorant.

A lot of engineering is highly counter intuitive.


*and this is an utterly misleading term to start with and the cause of
most of the confusion.



--
The lifetime of any political organisation is about three years before
its been subverted by the people it tried to warn you about.

Anon.