On 28/06/18 23:06, Vir Campestris wrote:
Imagine a wheel that was flat at the bottom so that it had half its
original radius. The rolling radius of the wheel is the radius where it
touches the ground - half the normal radius.


Oh dear...

This bit at the bottom is the only bit that counts. The rest is not on
the road.


Oh dear

A tank track doesn't have a radius. It isn't a circle.


Neither is your example above.


The effective
rolling radius of tank wheels is exactly the same as it would be if the
track wasn't there - it's just they are rolling along a track, not the
road. This is why it is called a track laying vehicle.

Right. And that is exactly the same effect as a tyre that has completely
lost its sidewall and is in fact just got a tread left.

So what we have, if you can picture it, is the rim rolling long inside a
tread that is ciurcular and bugger than te rim diameter,.

Ok so far? Now this is a ring gear and pnion in effect - a reduction
gera where the tyre is turning slower than the wheel

How can the tyre be turning slower than the wheel *if it has a sidewall
connecting them*

It cant.

What happens is taht all te other nbits of te tuyre connected to te rim
are actually pusing the ytrye tread around faster than the rim is going
so there is a relaticive angulra velocity between the flattened part of
te tyre and the rim above it.


This is wahy your 'bit at the bottom is the only bit that counts' is so
completely and utterly WRONG..

The bit at the bottom is not bolted to the rim. Its attached via a
flexible elastic medium, and its the flexing of that medium that allows
motion from all parts of the wheel and tyre to be transferred to the
contact patch.

Nothing says that the instantaneous angular velocity of the tread has to
match the instantaneous angular velocity of the rim, and in fact it
doesn't at the contact patch. All that has to happen is that the
AVERAGE angular velocity of the whole tyre has to match the angular
velocity of the wheel.


And that is where your thinking is totally flawed. You learned the
mechanics of solid wheels at O level, you failed to learn the mechanics
of more complex rotating systems thereafter.

Worse, you think you understand when you do not. Like dennmis, Huge,
harry T i m and all the other remooaners who run on received wisdom and
cannot actually think for themselves


--
The theory of Communism may be summed up in one sentence: Abolish all
private property.

Karl Marx