53" Pro version, fitment on a 2021 Hyundai Palisade. It is so much nicer to have it standing up and not laying on the ground. The new Aero model is far far superior then the Air, the sound is much clearer and sounds more meaty. According to the tape measure, her waist was 37", so we ordered her the 4XL which states that it is for 35"-37" waists. It is loud, very loud. These shoes are very comfortable and I really love the pinkish colour I bought. The dual mics were the determining factor that swayed me in buying these than a competitor brand. Im so glad I purchased these, since I love the sound and low latency of the earbuds they are covering. In the past, I also own Hoka One Ones (100+ miles) and previously ran on the Brooks Glycerin series (500+ miles per shoe). Nichts hat gedrückt oder gescheuert.