Can you put different width tires on a 2005 Mercury Mountaineer
P21565R17on front P24565R17 on back
You can put different width tires on your car without causing any problem. The P21565R1 and the P24565R17 do not have big difference and thus, they should be able to work well. However, your car mph may go down.
as long as they dont rub your fine. it might change your speedometer 1 or 2 mph.
With that system you need to have same size tires front and rear. You can put bigger tires on just have to all be the same size. That is your problem you are confusing computer.