Shortening the loan
I just shortened by car loan by 5 months by paying a chunk off the principal. The odd thing was that there were two options available to me on the finance site - "regular payment" or "principal payment". With the "regular payment" option, some of the money would go to the principal and some would disappear in interest. I'm not sure why that's even an option - if you're paying extra money into a loan you always want to pay it off the principal.