On 23/06/2018 21:47, Tim Streater wrote:
snip

Dunno what "rolling circumference" means, but the circumference can't
change, as it is fixed by the loops of steel belts in the tire (may
stretch a bit but not much).

*That* is the point.


Three points:

a. you seem to be assuming the steel is perfectly inelastic. When it
usually is made up of thin steel wires woven into cords and then into
belts I'd like to know it's actual modulus;

b. I posted a link to a paper which modelled tyres and reproduced
observed pressure effects. It noted that "the belt structure strongly
influences the effective rolling radius". But it also pointed to the
effects of pressure on the deformation of the tread - ie the stuff
between the belts and road. It seems to me credible that behaves
differently with changes in pressu eg just look at the sidewall when
pressure is low;

c. I introduced the term "rolling circumference" because how iTPMS works
can be discussed perfectly well without any reference to circumference.
So ISTM it behoves those who introduce "circumference" into it to define
what they mean. The circumference of the static, unloaded tyre? Or the
distance travelled for one rotation of the wheel - which all the
evidence shows does vary with pressure?



--
Robin
reply-to address is (intended to be) valid