If you put the hook under the wheel it would never be held in place and would rattle, bang and carry on something fierce as soon as the car hit the tiniest bump in the road. All of the stuff in the spare tire well has to be held down FIRMLY or you'll hear it all through the car. That's the purpose of the little spring with the loop. The loop fits over the center of the tire wrench which in turn is nested into the bracket at the side of the trunk floor. The wrench portion goes to the back and the bottom of the jack mast nestles in there as well. Then take the hook end of the little spring and put it into the bar with the spring on it that is above the slot in the mast for the hook. Flip the ratchet on the mast to "raise" and hand crank the ratchet up until everything is tight. Then to get it out, flip the ratchet down to "lower" and crank it back down to get the tension off the little spring. It all comes apart in reverse order.