On Wed, 27 Jun 2018 10:13:44 +0100, Tim Lamb
wrote:

In message , T i m
writes
On Tue, 26 Jun 2018 09:05:15 +0100, The Natural Philosopher
wrote:

snip

My point is that once te tyre is on and deforming, that relationship has
no validity or meaning. I applies to circle only. And the flatter the
tyre is the less circular it is.
Snip..

So, the tread under the load point shrinks reducing the unloaded
(true) circumference to an effective circumference and the real
unloaded radius to an effective radius.

This might be the answer:-)

Might? ;-)

The actual circumference varies with
pressure irrespective of the axle road distance.

Yes, the pressure affects the peripheral distance (effective
circumference) and that in turn affects the height of the axle over
the road (effective radius). ;-)

Cheers, T i m