The above recommendations are great, but...
Depends on what terrain you ride. The big S has a good tire in the Purgatory in a 1.9 flavor. I run one out back on my Epic and it hooks up great in all conditions. Maxxis also makes some decent stuff too. The Ignitor comes in a 1.95 flavor.
For the front, I am a big front WIDE tire guy. Like pushing the front end into corners too much and want as much MEAT up front as I can get. As close to 2.4s as I can get generally...
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Wut