To not believe in God, one would have to believe. It is not as simple as saying that you have NO belief, that would be an extension of Ignosticism, ignorant, hence no believe. You are saying that you don't believe, which must be something that you hold sufficiently strongly to say it in the first place... thus there is belief attached. If I say I can't see a table in front of me, because it is not visible to me, there is a lack of believe that it is there (if someone else is saying it is) but I would believe that statement, so belief is involved.
I think you should have the agnostic title, though really you are sure enough to say that there isn't, and are atheist, but don't like the title.
What most don't seem to understand is that there are three main titles, agnostic atheist ignostic, all of which have no believe as their definition. What is the point of three titles saying the same thing? None. So if you are sure, then you are atheist. If not, agnostic. This is extensions of what their main definitions are.
And your analogy of the car would be, I don't know