Calculate tire stress I'm trying to figure out how much stress is experienced by a tire while driving. Each tire can carry a maximum amount of weight, for a tire of 98kg this is 750kg per tire. A Tesla Model 3 weighs in at 1,611kg. I'm trying to calculate the stress on each tire while the Tesla is driving 80km/h but am not sure how I can calculate this?
 A: I think you are looking for an estimate of the circumferential strain on the inside of the tread portion of the tire as the car is driving.  Of course there will be an initial positive strain due to tire inflation.  Below, I will estimate the additional positive strain generated when your piezo element rotates from the top position to the bottom (adjacent to the road) position.
The top gray annulus represents the tire when unloaded.  The red line represents your element.  The thickness $t$ is the distance from the inside of the tire at $R_i$ to the outside of the tire at the tread.  Assume your element spans an angle of $\theta$ radians.
The bottom rectangle represents the same portion of the tire in contact with the ground.  This portion of the tire has been flattened out by the car weight.  We assume that the centerline of the cross-section shown in blue does not change length.  The accuracy of this assumption would depend on the exact construction and tread pattern.
When flattened out, the inside of the tire is stretched circumferentially and the outside of the tire is compressed.
The unloaded element length is
$L_0 = \theta{}R_i$.
The loaded element length is
$L_1 = \theta{}(R_i + t/2)$
The change in strain during driving is therefore
$\delta = L_1 / L_0 - 1 = ((R_i - t/2) / R_i) - 1$

