Broken Cord on Michelin Tire

[Neil & Pat]

Hi David, thanks for your interest in this very important topic.

In response to your questions, please consider:

1) Yes you can measure deflection but it is not easy to do with precision.
Deflection is the "change" in section height and can be measured in the
footprint (bottom) side of the wheel/tire as installed by taking the
distance from the road surface to the metal rim and comparing that to the
same measurement on the "unloaded" portion of the wheel/tire (top). That
figure, when expressed as a % change should be very close to a nominal value
of 8% for truck tires.
2) Yes the above measurement of deflection would change at speed due to the
centrifugal forces action on the unloaded portion of the tire. However,
deflection is a "static" measurement intended to be taken in a laboratory
environment not as we drive.
3) Your are once again correct, deflection of the tire is the ultimate
limitation for a tire because that is the primary factor in creating heat
thus effectively limiting the weight carrying capability of the tire.
4) In normal service there is no need to be concerned about the dynamic
effects of deflection or any other variability i.e. altitude, ambient
temperature changes, barometric pressure, etc. these issues are all fully
considered by the tire designer when the tire is first designed. It is then
fully tested to verify the accuracy of that work. All that remains is for
the tire builders to get it right and for the operator to do the right thing
by following the load/pressure charts provided by the manufacture and of
course avoid all the road hazards out there. Easy right?

Hope all this helps a little.
Regards,
Neil
Author, The R.Ver's Ultimate Survival Guide
www:rvsafetyinfo.com
Thanks Neil, that helps a great deal. Glad to see you here
on this list. Just a couple of questions:

1) can I measure "deflection"?
2) does "deflection" change as the tire rotates at speed?
3) sounds like the sole purpose of tire pressure is to maintain
the correct deflection?
4) if I were able to dynamically adjust runtime tire pressures,
would optimum tire life/performance be achieved by maintaining
the correct deflection under all ambient operating conditions?

.