I tested and reviewed the Continental Rubber Queen's (now known as the Trail King in the US) about a year ago, and thought they were a great tire. Brett Hahn the US Brand Manager for Continental, asked me to try out the UST version of the RQ's. Since then, I have bashed and smashed the tires through just about any terrain imaginable, and they have turned out to be stout, durable, with excellent traction and best of all are big and meaty!
For more details refer to my original and in depth article, Continental Rubber Queen Review.
The RQ/TK (Rubber Queen/Trail King) UST comes in 2.4 and 2.2 sizes. The 2.4 is a monstrous tire, both in weight (1130 grams) and girth (2.45"), and feels more like a downhill tire than its non UST version. The 2.4 is made in Germany with the Black Chili compound, the Apex sidewall and three plies of 110 tpi (3/330). The 2.2 seems tiny in comparison, but still comes in at respectable (and accurate) 2.2", and is decently light (802 grams). The 2.2 is made in Taiwan out of a normal rubber compound (no Black Chili), and also uses three plies of 110 tpi (3/330). The tires use a modified paddle shape tread pattern (thanks Shiggy), and have a round profile in which the knobs don't stick out as far as casing.
The Black Chili (BC) compound does help a tad on wet roots and rocks, and gives a slightly more pliable sidewall (defter touch), but the burlier and thicker UST sidewalls make it not as noticeable of a difference, so the non BC 2.2 isn't missing that much. Meaning that BC doesn't make a wholesale difference in how the UST tire performs, at least in direct comparison to their non UST tires (BC vs non BC), due to the stout UST sidewalls.
Installing the 2.2 was sort of a wrestling match the first couple of times, since the bead and sidewalls are not as pliable as the 2.4. I swore more than a few times prying them on! Once either version is installed, they pop up on the tubeless rims pretty easily. I used a compressor, since a good shot of 70 psi throughput helps seat them at 30-35 psi.
The 2.4 are huge and heavy, big and meaty, and let you roll over anything, especially at high speeds. I liked the slightly smaller 2.2, since they rolled better, were lighter (better acceleration), and still had an exceptional tractor pulling power, even in loose conditions. The 2.4 had a very slight edge due to the Black Chili, but 2.2 wasn't far behind. I preferred the 2.2 as a pair, or I sometimes used a normal 2.4 in front with the 2.2 UST in the rear. I have also had issues getting the 2.4 to sit evenly on the rim, since they have tended to wobble a minutely, much like fat downhill tires tend to do. The 2.4 are nice to have if you know you are going to be living in rock gardens or doing some extreme riding, else they are a bit ponderous and have poor rolling resistance.
The benefits of a true UST are the ability of running low pressure (25 psi and less) without burping, no sealant (or at least less) is required and a tougher tear resistant sidewall.
Either size is extremely durable and near bombproof. There was a reason that a lot of bike vendors were using the 2.2 UST at the 2009 Interbike Outdoor Demo, they are tough, and they work. The Demo riders were not coming back with flats nor tears, which regularly happen at the notoriously abusive volcanic rock terrain at Bootleg Canyon.
2.4 UST - 1132.8 grams and 1129.1 grams, Carcass 2.45"
2.2 UST - 801.4 grams and 802.4 grams, Carcass 2.2"
I liked the 2.2, it rolled well, was stout and had some good tractor like traction. The 2.4 was the girth monster, that could take any anything tossed at it, although it was a sluggish roller. Both tires are grippy, big and meaty, puncture resistance, and have the tough UST casing and bead. The 2.4 is huge, so make sure your rear triangle has clearance for them.
The Rubber Queen/Trail King UST is an excellent choice for an "All Around" tire, especially where abusive terrain can slash sidewalls and cause pinch flats.
Rubber Queen/Trail King Specs:
2.4 UST - 3/330 tpi casing, with Black Chili compound and Apex sidewalls, foldable, 26x2.4"
2.2 UST - 3/330 tpi casing, with Apex, foldable, 26x2.2"
Rubber Queen url: https://www.conti-online.com/generator/www/de/en/continental/bicycle/themes/mtb/downhill_freeride/rubberqueeneng/rubber_queen_en.html