In the classic game, a binary search is the most efficient, assuming randomness.
After reading your post again more carefully, I think I understand the situation better. Am I correct in supposing: For each attempt, you can change as many sliders as you like, and the hints won't change until you press some sort of "submit" button? Otherwise I don't see how 6 attempts is nearly enough to accomplish anything.
I'm also curious: is it safe to assume all variables are independent, or would we think that tyre pressure front should be comparable to tyre pressure rear, or something like that?
I can't think of a good algorithm offhand, but it doesn't hurt to know better what we're dealing with first.
Problem seems interesting, by the way.