RPMrush, what size tire came on your 18x4 rim? I recently found a spare tire from a 2013 Genesis sedan (18x4 alloy) and the tire size is 155/80-18 (Hankook S300). This tire is a much larger diameter than the standard 19” tires and there is no way this tire/wheel will fit in the spare tire well like in your pic (I’m not even sure it’ll fit on the car). I’m guessing your tire is actually a smaller size? When you put it under the floor, does the floor lie flat or does it end up sitting raised up from normal? I’m guessing you fit it in fully inflated?