2.1 is an awfully narrow tire for a trail bike. I'm 165lb and I ride my XL Heckler with 2.35 Nevegals summer, and 2.4 Enduro Pros fall/winter. 26-28 psi for the rooty/rocky/slippery stuff we got in the Pac NW area. 30-34psi when I'm riding where snake bites might be a problem. If you are running 2.1's because you are worred about 'sluggish' response, you bought the wrong bike for the type of trails you're riding.