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

I bet you can understand i or j and how it represents the square root
of a minus number (something that is impossible in straight maths) but
you can't accept how a tyre can change it's effective circumference /
radius when it running at a lower pressure??

--
Tim Lamb