Dogs save it up and pee on everything they can, a little at a time. So tires are just one more thing.
I don’t have a dog but I’ve walked my sister’s dog on visits. The peeing I get. I don’t get what’s up with the poop. The little monster seems to only get the urge to take a crap while on the nicest lawns in the neighborhood. I have actually stood around in the small wooded area and nothing happens, but the second he’s on a nice, well-maintained lawn the haunches go up and the butt points down.