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

sabino56's post helps clarify some of the misconceptions occuring in
this thread:

https://www.hotrodders.com/forum/how...er-101007.html

and in brief:

1) the diameter does change with load/pressure/speed

2) the effective radius does change with load/pressure/speed

The effective radius has more affect on gearing than on diameter.



--
AnthonyL