Hello, Racer,
For bending of a flat plate (let's say the undertread), the strain energy is proportional to the plate thickness squared. Your story fits perfectly with the theory.
That leaves open the question of exactly how the grooved tread participates because the strain is mostly taken up in the groves where no work is required, or at least much less.
Since the wear of the tire is in the grooved part, we would expect thickness change there to have somewhat less effect--and it could depend on the the tread design.
Well, heck, you could probably teach us a thing or two about how tread design affects tire rolling resistance.
Ernie Rogers
Quote:
Originally Posted by CapriRacer
Anecdote:
You may be aware that I work as an engineer for a major tire manufacturer - who will remain nameless. Background to this story: At least one major vehicle manufacturer requires tire suppliers to monitor the RR of the tires being supplied - and that task is assigned to a QA engineer.
I was once asked to document all the changes made to a particular tire - and I ran across an entry where a new tread die was made to bring the tire back into RR compliance. I asked the QA engineer in charge what was with that - and he proudly whipped out a graph showing the RR by date and a gradual upward trend. He stated that the die used to extrude the tread component wears over time and gradually the tread gets heavier (and thicker). By making a new die, the tread was brought down in weight and the tread thickness decreased, and the RR was reduced.
BTW, the mold doesn't change so what would be measured as tread depth would not change. All the change in the volume of rubber in this anecdote is between the bottom of the groove and the top of the casing. This dimension is commonly called undertread.
Ergo: Change in tread rubber weight (volume) = Change in RR
I've encountered this principle in several studies of RR, but it's usually expressed as a "throw away / background" comment - as though this is so fundamental that it doesn't need validation. Perhaps it is because the studies that back this up are quite old and out of print.
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