I had always run the same size F and R but recently switched to a 2.3 Specialized Ground Control up front and keeping a 2.1 on the back. I found that I corner faster and more securely, roll over stuff easier and descend with more confidence. Amazingly, the 2.3 was no harder to push even though it is wider and a few grams heavier. I actually go faster with this tire. I'm a XC racer who keeps it on the ground--any air I get is incidental, lol.