To be honest, it wasn’t love at first run.. I went through three pairs of the Glycerin 12 and LOVED that model. I wasn’t thrilled when I slipped my foot into my first pair of the 13’s and realized that the entire feel was different. It was heavier and cushier (which was apparently exactly what I needed). Regardless I trained and ran my first marathon with the Glycerin 13 and I love it! I’m now onto my second pair along with a new pair of the Glycerin 14.