Back in 1926, when I. J. Cooper produced his first tire, his policy was "Good merchandise, fair play, and a square deal." We found this to be true in this century when we used our first set of Cooper Discoverer A/Ts (Jan. '02).
As you can tell from this photo, the Cooper STTs do a great job of self cleaning.
So impressed were we with these Coopers in cold-weather operation, we wanted to try a more aggressive tire that would perform well in all types of terrain. Well, we weren't disappointed at all when we mounted up a set of 33x12.50-15 Discoverer STTs on some 8.5-inch American Eagle Alloys. STT stands for "Super Traction Tread," and indeed it is. Just looking at the tire, we knew Cooper had a winner here.
Starting out, there are the three-ply polyester sidewalls that Cooper calls Armor-Tek 3. There is also the rim-guard design, which depresses the bead seating area around the rim flange for better protection from rock damage. Under the tread are three more poly plies, along with two steel belts, that make for a C-range load capacity.
As to the 9.7 inches of tread design: It's unique in that the lugs extend off the tread and follow down the tire's sidewall. This provides not only sidewall protection, but additional traction in certain conditions. One of the problems we've seen in the past with tires that have sidewall lugs is that when air pressure is lowered, these lugs provide a bit more sidewall stiffness. That can cause the center of the tread to cup inward, resulting in less tire contact. Not in the STT. It took a bit more air reduction than usual to get the sidewalls to bulge, but these tires put down the perfect rubber contact patch.
The tread's design also offers numerous biting edges at various angles, which makes the tire quite aggressive in every type of terrain-maybe a bit too aggressive for sand, but they did quite well in our favorite mud hole, self-cleaning with a bit of heavy throttle application in all but the thickest mud.
In the snow, the tire grabs and holds snow, and then releases it on the next revolution to
Ice and snow: We ran these tires throughout the summer months last year, just waiting for winter to arrive and some heavy snow to try them in, and we were not disappointed with the results. The excellent flotation quality of the Cooper STT is a benefit to staying on top of snow, and the tread didn't cause excessive digging. It's our opinion that a good snow tire has to grab snow, hold it in one full turn, and then discharge it before it's compressed to ice. The tires scored some high points here. One of the problems with a wide footprint on ice is the lack of ground pressure that prevents good traction. The numerous biting edges, plus the tread block sipes, even surprised us as to the tire's ability to provide excellent traction and stopping power on icy roads.
Noise? So far, average, but tire noise can change either for the better or the worse as mileage builds up.
Road manners are surprisingly quite good for tires as aggressive as these. Tracking is straight and true without a tendency to follow pavement ruts. Hard braking on pavement brought straight and true stops. Sidewall stability is what we would expect from a quality tire that measures just under its advertised 33-inch diameter. We are sure the three sidewall plies have something to do with that.
Tire: Cooper Discoverer STT
Load range: C
Max load (lb @ psi): 2,205 @ 35
Sidewall: 3-ply polyester
Tread: 3-ply polyester, 2-ply steel
Approved rim width (in): 8.5-11
Tread depth (in): 21/32
Tread width (in): 9.7
Section width (in): 12.08
Overall diameter (in): 32.76
Static loaded radius: N/A
Revolutions per mile: 1,231 (approx.)