On 23/06/18 17:01, The Natural Philosopher wrote:
On 23/06/18 13:42, Chris Hogg wrote:
On Sat, 23 Jun 2018 17:04:38 +1000, "Jeff" wrote:



"Chris Hogg" wrote in message
...
On Sat, 23 Jun 2018 16:08:44 +1000, "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.

Does it?

It clearly does with the distance between the axle and the ground.

I think we're at cross-purposes here. Obviously, as you say, when a
tyre is flat, the axle is nearer the ground. But is it reasonable to
regard that as the radius of the tyre?

Not if you have any understanding of mechanics.Â* The whole tread, up to
and including a caterpillar track, goes round once per revolution of the
track or tyre.

THAT is what determines the RPM/speed relations ship.

A revolution is the movement of one object (*point* on circumference)
around a centre (hub).
Your caterpillar track is supported by wheels, each of which will do
many revolutions for one revolution of the track. The circumference of
the track is many times the circumference of each wheel.


What happens with tyre pressures is quite clear. The tread stretches
slightly under higher pressures. How much will be a function of the tyre
construction. And this is what the sensors rely on.

No.
Since no wheel is circular using radious as a concept is plain wrong. At
best you can calcualate a '*radius it would be if it were round*,' from
the actual circumference.

The use of radius is completely right.
The circumference doesn't change. The centre of the instantaneous circle
moves closer to the radius.
The tyre is a three dimensional structure and this debate is being
conducted in a two dimensional manner.


For it to be any other way the tyre must slip on the rim or on the road,
substantially.