Since silicone is about the best lubricant known why do they sell it for us to spray on our auto tires doesn't rain wash it into the tread and roadway below for the next driver to skid upon?

Answer 1

Silicone is not water soluable, so there will be very little that will be washed off of tires in the rain. The amount that might go from the tire to the road surface is so microscopically minute, especially across something as great an area as a road surface, that there will be no effect on other vehicles on the road, especially when you consider that a road surface is very pourous. Of far, far greater concern is all the other fine lubricants found in an automobile like engine oil, Transmission Fluid, power steering fluid, and so forth, that manage to find their way out of cars, onto the road surface. These fluids are the worst at city intersections, where cars stop, and stuff leaks out while they sit there. Then, when it rains, the surface becomes like ice, and can potentially cause an accident.