Rain usually just cakes the dirt. Unless it's a downpour, it doesn't move with enough velocity or volume to remove the dirt. So the dirt just gets damp, maybe moves a few cm with gravity, then dries as a mud cake.
replySee this all the time in Phoenix metro: A light rain just pulls down all the dust in the air and deposits it on the car. It has to be fairly sustained to wash away the initial dust collection, and even then you can still see dust on the paint.
replymy experience is that unless you get some really torrential rain, it's not enough to clean the sand/dust/grime
replyCan confirm, my car doesn’t get cleaner unless there’s a downpour
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