I'm long winded to get to my point but bear with me:
When i purchased a used bike this past summer ( a 2009 Trek Fuel Ex 6.5 ), It came with a pair of the 2.1 Kenda nevegal Stick-e tires. Riding them regularly throughout the summer I noticed what most people do with these tires, that they were wearing down FAST, eventually, knobs started shearing off the rear tire and it was time to start shopping around. I saw a review for the Specialized Clutch 2.35 tires over at Pinkbike and as I had been wanted a beefier tire, I thought these would be a perfect fit for my next tire.
:out:
I rode these for a month, and the entire time I was thinking that there was something physically wrong with me. I actually stopped a ride midway through at Jacobsburg, dry heaving, because I was working so freaking hard to keep up with the gang. No matter how hard I pedaled, it wasn't enough to keep up with the group. Then my buddies finally convinced me to "consider" that it was in fact my tires that were slowing me down. I'm new to all all things Mountain Biking, so this was hard for me to swallow because really, how in the world could a little extra rubber or a knobbier tread really impact your ride?? On my next ride I threw my decrepit Nevegals back on and I literally turned into Rocket Man. Uphill and Downhill (a little scary with all my knobs torn off), I could not be stopped or caught up to. This lead me to 2 very important revelations:
1) If you really want to kick some butt around the trails, strength training with a Set of Clutch tires can't be beat.
2) There might be something to this theory of "rolling resistance"
So with that in mind, I'm again looking for beefier tires but I simply cannot endure (again) what I did with the Clutch tires. I don't want my tires to slow me down or kill me with exhaustion. I came across the WTB Weirwolf 2.55 LT (discontinued but still available for around $35/tire). Its got great reviews on MBTR but I'm hesitant of the Low Tread design. http://www.mtbr.com/cat/tires-and-wheels/tire/wtb/weirwolf-2-55-lt/PRD_4...
So the real point to my whole diatribe is....how important is tread depth (Front Tire only) for your typical riding in our area. My rides break down like this:
70% CamelBack Gamelands (Fireroad only out of necessity)
10% J-burg
10% Allamuchy
5% Glen Park
5% Sals (just started here, and will go loads more if I can get over the creepy dudes in their hoodies 
)
As this is my first season really riding, my skills are still developing and I'm not an overly aggressive rider, but i'm trying!
Your thoughts?