It would be quite handy to know what type of terrain, trail conditions and trail surface you wish to have a tire perform well in, for example do you wish to have one that works great for fast down technical (rocky and rooty)? One that grips well in muddy conditions? Do you want light-weight, fast rolling for dry, smooth singletrack? You will find that there are a good number of very, very good tires but each has its characteristics and compromises..A big fat cushy, sticky and knobbly downhill tire tends to be superb for technical downhill applications but are heavy, have sweat inducing rolling resistance on flats and steeps and generally suck for regular tame smooth trails..just the wrong tire for the wrong application yet it'll get 5-of-5 stars once reviewed and used for it's specialty. Fast tires tend to not have the best grip, puncture somewhat easily.
Right off the bat, the x-kings do look like a pretty nice tire. I have just had no experience with it say one way or another how it performs.
You really end up getting the "right" tire for the particular trail you ride and the type of riding you do.
Sorry not very helpful in stating what a 'top shelf' tire is, but again it all depends, it truly does. Schwalbe, Maxxis, Continental, Panaracer, Kenda are just some of the very well regarded brands.
I'll give you a for example of the tires I have on my bikes, although I like the tires I have a lot other more experienced riders might have more experience with a broader array of tires out there. I certainly am only familiar with a few because I use them, others have the experience of using dozens and have more fine tuned advise that I can offer.
On my SS Rigid 29er I have 2.1" Maxxis Crossmarks F&R, I tend to use my SS on fire road, gravel paths, and moderately technical (roots and rocks) in SE PA singletrack. These tires roll very well and I have not had any torn sidewalls altough I go thru pretty rocky areas. I really like these tires I dont tend to ride when it's actively raining out but I hear some folks say that on especially steep terrain on looser soil and across wet logs they have a tendancy to lose traction. I have not pushed this particular bike across that threshold in this scenario so for my application it has so far been stellar.
I have an FS AM bike that has WTB Prowler 2.5" in front and WTB Stout 2.3" in the Rear. They are quite heavy tires, are not appropriate for smooth singletrack as they have a high rolling resistance, you notice the extra effort and energy you expend pedaling and on soft ground and especially sand it'll wear you out...BUT when bombing down long steep technical descents I have cushion, control and grip to a degree that it is confidence inspiring. They are fat, cushy, sticky, knobby, heavy tires that are good at it's specialty but a chore for regular trails. I only ride this bike if I know I'm going to bomb down fast steep rocks, roots, loose descents...alas for me in order to go down I have to climb up and it kicks my @$$ when I do it...so into the granny gear I go and grind away until I make it up (or walk it up)...dems tha breaks! These tires on a big burly FS bike that probably weighs not too much under 40LBS is going to be a lot of work.
My XC 29er has Continental Race Kings 2.2, a great tire for smooth to mild terrain. roll quite well, have shallow tread that does not work so great in the wet or highly technical. Good at rolling over obstacles but not especially at "clawing" over them. A good lighter-thus-thinner tire to give you speed and control within it's performance envelope. Generally pretty grippy compound so does show some wear faster than others I have but not excessively so. A great tire if you need to race and ride a while when the weather and trail conditions are good (dry to damp)
That's just some...I have other bikes with other tires but you get the jist.. Also what is not uncommon is to get different types of tires for front and rear depending on the characteristics.. Easier rolling thinner (2.1" for example) on the rear with a grippier slightly more aggressive tread pattern for the front to give traction and control for descents and higher speed (2.3" for example) especially if you ride a trail with terrain varied enough to give you reason for specialization at either end of the bike..not an uncommon thing to do for Trail, AM and DH bikes.
The folks at forums.mtbr.com are great at drilling this detail down as they are purely dedicated to mtb and have a lot of knowledgeable folks.
Remember..state what bike you have, as best you can your terrain/trail and what characteristics you wish for..speed, traction in ups and/or down, wet/mud, bombing across and over roots and rocks...
Last edited by Moozh; 07-02-11 at 09:06 PM.