One consolation is you can claim that depreciation against your income. By the way, what type of car do you own? That's a huge drop.
If I understand your concept correctly the flaw in your plan is that new cars depreciate dramaticly, especially expensive ones. If you have an interest only loan in 5 years you will owe $60K and the car will be worth $20K if you are lucky. I drive a nice 5 yo car that when new was $50k. Have just been offered $8k as a trade in. Think I will keep it a while.