The Cooper Discoverer STT radial light truck tire is the latest and greatest incarnation of the Cooper Discoverer line. It's available in a variety of sizes ranging from 30- to 37-inch diameters and fits 15-, 16-, 17-, and 18-inch wheels. C, D, and E load ranges are available.
The Cooper Discoverer STT is the latest version of the company's Discoverer tire lineup. In addition to a very functional and visually appealing tread design that includes deep buttress lugs that extend down the sidewall, the new Discoverer STT uses the company's unique Armor-Tek3 carcass construction. Armor-Tek3 employs use of two radial polyester body plies and one angled polyester body ply. In all, three plies encompass the tread area to achieve excellent resistance to impact breaks and bruising. The computer-designed, nondirectional STT tread is the best off-road design yet of the Discoverer tire line. STT stands for "Super Traction Tire," and Cooper isn't far off with this designation.
The Cooper Discoverer STT performed exceptionally well in hard-packed and soft dirt terrains and also shined on the rocks. Initial rockcrawling attempts on obstacles while at a higher psi were acceptable but improved greatly as we lowered the tire pressure. The Cooper Discoverer STT seems to have a natural ability to conform to rocks and even more so once the ideal off-road pressure is determined. We felt comfortable dropping to 10-12 psi using our nonbeadlocked Pro Comp wheels and would perhaps go even lower should the terrain call for it (and at a time when we are better prepared to slip the tire off the wheel, should that occur). Nonetheless, the 10-12 psi range appeared to work well for this tire while in the dirt and rocks; the loose dirt, almost sandy, sections were also easily conquered with the Discoverer STT tires in this psi range.
Another benefit of these tires are the beefy, scalloped shoulder lugs that extend from the tread down the sidewall. These tread blocks are great aids in a variety of conditions but were especially helpful in obtaining and maintaining traction on rocks where it was necessary to ride the sidewall to clear the obstacle. The side lugs also offer increased obstacle coverage when aired down, which not only helps save the sidewall area from undue wear or damage but also permits continued traction across the entire contact patch of the tire.
The STT's street manners were also up to par for an aggressive-tread tire of this type. On-road handling was easily manageable and seemingly unaffected by the larger tire size or tread. Steering response also remained fairly nimble and road noise was minimal compared to that of similar tires we've tested.
In all, the Cooper Discoverer STT proved itself a very capable and user-friendly tire. It has the attitude of a mud-terrain tread but still responds with authority to highway and other on-road driving situations. Aside from its impressive performance abilities, we also really liked the design and appearance of the Discoverer STT and received similar impressions from all others we encountered who noticed the new treads.
Due to the design of the tread, rocks caught between the lugs are easily ejected upon a complete rotation of the tire. An integral stone ejector rib is in place from the center lugs to the buttress blocks and helps stones from becoming lodged. The center and side lugs also feature sipes to further its capabilities. | 
The deep lugs offer ample digging ability in mud, sand, and snow, and the notched and scalloped shoulder lugs further its capabilities in rocky terrain where, when combined with lower tire air pressure, they help the tire conform to whatever obstacle is at hand. A rim flange protector is also in place to help alleviate damage to expensive wheels. | 
The 35x12.50R15LT size offers a C load range and measures just under its claimed 35 inches, making it nearly a 36-inch tire by some manufacturers' sizing guidelines. The tire can be installed on an 8.5- to 11-inch rim and handle loads up to 2,535 pounds. |
ORW in San Diego mounted and balanced the 35x12.50R15 Cooper Discoverer STT tires on a set of 15x8 Pro Comp Rockcrawler Xtreme steel wheels. | 
The soft rubber compound helps the tire better conform to rocks and other obstacles, and the deep center and side lugs also create aggressive capabilities. We aired down to about 12 psi to maximize the tires' footprint for increased traction. | 
There was no stopping the Discoverer STTs through this rocky trail. The tires met the obstacles capably and never left us without traction when it was needed. |