I don't get the, "Mud in the tires."
When Vinny and Lisa first come to town they comment how there must be something wrong with the wheels.
A passing black man, dressed in a mechanic jumpsuit, says something about mud in the tires.
Vinny questions this then the black man explains that it's just an expression while he also said there is mud in there.
Meaning there is not actual mud in the tires but they make it seem as if there is mud in the tires.
If there was mud in the tires then why would he say it's just a figure of speech?