The reason automobile and motorcycle tires have grooves is to channel water out from under the tire to prevent hydroplaning. Although we avoid riding in the rain I can only assume the grooves on pneumatic tires are intended for the same purpose. Otherwise it would be better to use slicks. I have noticed that pneumatic tires on skateboards aren’t always mounted with the grooves mounted in the same direction. The Six Shooters I mounted on my BIW (build in work) really highlight the issue because the groove direction is so obvious.
I found this explanation of grooves on motorcycle tires, which are mounted differently for the front or rear.
The stated reason is that most of the acceleration comes from the rear tire and the braking from the front. Since we brake and accelerate from the rear that doesn’t apply. IF I follow the logic correctly our front tires should always be mounted like motorcycle rear tires, with the grooves channeling water outward while the tire rolls forward. I guess the rear tire mounting depends on whether you are more interested in accelerating or braking. I think I know the answer for most people using 12s6p batteries on their boards. We should mount front and rear tires like motorcycle rear tires. If you consider the grooves as an arrow the arrow points in the direction of rotation.
That is a lot of speculation. Does anyone know the answer instead of guessing like I am?