No tread on the tires
Refers to the tightness of a girl's vagina. If a girl has a loose vag, she is said to have very little (if any) tread on her tires.
Hey, how was hooking up with Sarah last night?
Let's just say there's no tread on the tires.
She was that loose?
It was like throwing a hot dog down a hallway.
Gross.