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Cooper Discoverer STT Tire Test

A mud tire we can easily live with on the street

Jimmy NylundPhotographer, Writer

Cooper makes enough tires to rank eighth among the world's many manufacturers, yet you don't see many of them on the trails. That may well change with the new Discoverer Super Traction Tread.

We were lucky enough to get our hands on the first set of production tires last summer, and if the performance of those 31x10.50R15s is any indication, you should see more Coopers on the trails soon. So what is it that makes this Discoverer work so well? Polyester has been a favorite casing material in the tire industry since 1963, so there's really nothing new about the STT's 3-ply polyester construction, and two steel belts is pretty much the norm for radials. That means the nicely rounded tread area is largely responsible for this Cooper Discoverer's performance.

Generally, a flat tread area works better on pavement, as does a mild tread design, but the Discoverer STT doesn't seem to follow those rules. With a generous crown radius and a quite aggressive 20/32-inch-deep tread, we certainly hadn't expected a quiet ride, but were rewarded with less noise than many all-terrains emit. For the first few hours, we noticed a slight floaty feeling, but it disappeared (or, we got used to it). Rolling resistance was also surprisingly low-again, better than many all-terrains. Between the low noise and rolling resistance, the STT should theoretically deliver good mileage, and our gas log indeed confirmed that assumption. Yes, it requires fuel (energy) to make tire noise.Cornering was stable and secure, tracking was practically nonexistent, and irregularities in the road were soaked up quite well. There just wasn't anything to complain about as the large-siped lugs and tread blocks simply did their thing on asphalt and concrete. These Discoverer STTs did it smoothly too, with one tire showing a mere 3 pounds of Road Force Variation, the others averaging 22 pounds. Tire technology sure has come a long ways since traction treads debuted in Europe in 1904.

Hard-packed dirt was probably the STT's favorite substance, where the 8.3-inch-wide tread would rarely slip. As the layers of loose dirt got deeper, the rounded casing helped maintain a good grip, and even in shallow sand the STT worked better than some all terrains, despite the aggressive tread. Having about 1,600 pounds of weight per tire on a smallish 31x10.50's footprint didn't work out all that well in the truly loose stuff, however, pretty much regardless of inflation pressure. That's not the Discoverer's fault, as they now come in sizes much better suited for heavy vehicles on soft ground, such as the 34.85-inch-tall 35x12.50R15 with a 10-inch-wide tread. Our high contact pressure really paid off in the rocks, however, where the siped lugs would not readily slip even on smooth boulders.

While it'll likely have rained in sunny SoCal when you read this, the five-year drought didn't provide any mud in time for the STT test, but the tread looks very capable and has good self-cleaning features built in.

In a way, the Cooper Discoverer STT is more of an all-terrain tire than many A/Ts are, largely because of its rounded casing, which helps quite a bit in the dirt. Despite its aggressive tread, the STT is also quiet and very well-behaved on the street. Most likely it is a good mud tire too, and that's about all you could ask from a tire. Heck, the STT even has raised white letters, if you need them.

Tire: Cooper Discoverer STT
Size: 31x10.50R15LT
Type: Radial
Load range: C
Max load (lb. @ psi): 2,270 @ 50
Sidewall: 3-ply polyester
Tread: 3-ply polyester, 2-ply steel
Approved rim width (in.): 7-9
Tread depth (in.): 20/32
Tread width (in.): 8.3
Section width (in.): 10.9
Overall diameter (in.): 30.5
Static loaded radius (in.): 14.0
Revs per mile: 681
Weight (lb.): 48