The ability to choose.
You can't be serious. Yes, of course the design of the car doesn't have an impact on your decision-making process. But I'm not talking about the design of your car. I'm talking about the design of your brain, or your soul, or whatever you think is the origin of your decisions. The structure of that has been designed, not by you, and that structure dictates the way in which you make choices. You cannot make a choice free from the design of that structure, so your will is not free.