There are two 2015 Acura MDX OEM tire sizes—P245/60R18 and P245/55R19—but to know which one you’ll need, you first need to understand your vehicle’s rim size is. Fortunately, figuring that out isn’t very hard and there are only two sizes they can be—18 inches or 19 inches in diameter.
If you don’t know what size your rims are off the top of your head, you can use a measuring tape to find the diameter yourself—simply measure from bead-seat to bead-seat across the face of the wheel.
If your 2015 Acura MDX has 18 inch rims, your OEM tire size will be P245/60R18—but if you have 19 inch rims, your OEM tire size will be P245/55R19.