Quote:
Originally Posted by Ernie Rogers
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
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Here's the deal about the tread elements - the opposite of the grooves.
When you bend a flat plate, the surfaces are either put in compression or tension. In the case here, the "plate" is being unbent, and the base of the tread elements is being compressed.
But there is another factor to consider: Pantographing. That's the word that is used to describe what happens because of the cords in the tire.
If you consider the individual cords to be attached to the adjacent layer, what you have a a series of parallelograms. So as the tread enters the footprint, the undertread "unbends" and gets shorter (it is traveling along the "chord" and not the "arc" of a circle), so the width gets wider.
That means that not only is there movement in the radial direction (We're calling it "bending") and movement in the circumferential direction (because of the "chord" effect), but there is also movement in the lateral direction.
Another thing to consider is that compared to the cords, rubber is very flexible. So changing the tread rubber has an unusually high proportional affect on the energy not returned, compared to its effect on stiffness.