Given that the car drops nearly 50% value as it leaves the lot, I'm not sure how this every pencils out before maybe 10 years 100k+ miles...Maybe these days given how hot the used car market is (driven by the expensive nature of newer vehicles), but again this is a chicken/egg problem.
Your loan is exceedingly abnormal or from a past time as the average loan % in the US is much higher on that time scale.