Lyric discussion by plonkeh 

Cover art for Slide lyrics by Ani DiFranco

I think that line refers to being a slave to her sexuality, being unable to resist the "tractor pull". Much like in the song "Out of Habit" where she says that her cunt is like a wound that wont heal.

It's not there for shock value- she's trying to explain how she feels compelled to have sex. This could either refer to doing sex work, or just having sex in general. I think the talk about the bicycle ride in the rain (if you try to stop you slide) is about how difficult it is for her to stop (to put the breaks on, cause she'll slide).