I never thought about the tires throwing more stuff up!
I had those auras a couple of times years ago - migraines without headaches.
It is proving to be great fun 'Bent. The season might be over before I get back to get you a test - unless you're willing to get really mucky in the spring mud.
Bash: the tires throw a grimy rooster tail a good 15m back so you don't want to follow get close. For me the aura will become a headache if I don't address it within 10-15 minutes. If I catch it, I get away with a might of mush brain for 4-30 hours. I actually appreciate the early warning, even if it can be inconvenient.