The Discoverer tire's aggressive, deep tread put this tire above the rest. Many other tires tested over the years have also performed admirably, but they had also been ambivalent in both design and performance.
Discoverer STTs offer deep shoulder lugs and a unique center traction zone that creates a bold, aggressive tread for superb traction, even in gumbo mud. The open design keeps the tread pattern clear while the tire's rotation slings away even the stickiest mud.
On the downside, the Discoverers are noisy on the freeways (they vibrate at slower street-driving speeds), and they offer stiff riding until you drop the air down to about 15 psi. Off-road, however, they work with a vengeance.
How is this, you ask? They were tested from Baja beaches to Rubicon rocks, which included sand, boulders, washboard, pavement, mud, not-so-dry lakes, and everything in between. In the year that these Cooper tires have been guided through their paces-18,286 miles worth-the wear-and-tear miles were accumulated in various functions: as daily runners to and from the salt mine, towing a camping trailer (both on- and off-road), while flat-towing the Scrambler, and off-roading.
These tires were tested from Baja beaches to Rubicon rocks, some of which are shown here. With air pressure set at 18 psi, rocks-sharp, pointy, or round-presented little problem for the rugged Cooper tires. The Cragar aluminum wheels, however, took a pretty good pounding through the sluices.
The Scrambler on which the 33x12.50R15LT Discoverer Radial STT (Load Range C) tires and 10x15 Cragar Trucklite aluminum wheels were tested weighs in at 3,840 pounds with its Superwinch and TJM front bumper/grille guard. It is equipped with a 258ci inline six-cylinder engine, T5 five-speed transmission, 4.10 gear ratios, and Lock-Rights in both differentials. These details are mentioned because weight, engine/transmission type, and lockers can cause different performance and mileage results. For instance, V-8s can sometimes spin tires more aggressively, resulting in accelerated tread wear. Likewise, auto trannies normally use up less tread than do manual transmissions, and lockers chirp off rubber around almost every turn. Compare this equipment with your own vehicle, and determine how these tires would wear on your rig.
With this engine/gear ratio combination, it was determined that 33-inch tires, while not being ideal (an inline 258 six is stretched pretty thin with 4.10s and 33s), would work OK on the freeway and great in the dirt.
A bit of showing off in Dry River Canyon in the Los Padres National Forest on a trash-pickup day. El Niño storms had toppled solid chunks of compacted soil from the high vertical cliff-face, which needed to be broken up, or future rains could create flooding from the water buildup.
These tires are available in several different sizes, which means they can be matched to almost any truck/engine/gear ratio combination. We chose the 33x12.50R15LT Discoverer Radial STT tire because of its aggressive tread and height. These tires are Load Range C (which gives them a maximum weight-carrying rating of 2,225 pounds at 35 psi), with an overall diameter of 32.5 inches, overall width of 12.8 inches (13.7 inches loaded), and a tread width of 10 inches. They are also designed to mount on 10-inch wheels.
Speaking of wheels, we mounted the Discoverers on 10x15 Cragar Trucklite aluminum wheels. This was done for two major reasons: looks and reliability. For many years, Cragar has offered some of the best-looking and most reliable aluminum and mag wheels to the off-roading public, and these Trucklites are no exception. They've withstood Rubicon rock rash, boulder bashing, and Baja beach sand as well as any steel rim we've ever used. The only downside is having to use special, deep lug nuts for mounting. Normal-sized lug nuts and lug locks will not work on these wheels.
Traction was so impressive with these tires, we were able to negotiate the entire Rubicon Trail with a USA VentureCraft TrailBlazer tent trailer in tow. Although, with the weight of the trailer and the 33-inch height of the tires, the Scrambler's six-cylinder engine and 4.10 gears were just barely strong enough to pull us up some of the steeper sections.
These tires gave us such traction confidence that we tested them on some of the most adverse trails in the two Californias, and-other than in sand-without lowering the air pressure. A conscience decision was made early on to test the mettle of these awesome-appearing radials at full on-road pressure-32 psi. Even though this caused a rough ride on the Scrambler, it gave the tires their "bona fides." From sky-high Sierra Nevada rocks, to Baja California sand, or to a desert trail that combines rocks, boulders, and mud, these tires lived up to their name. The higher pressure protected the tires while sliding over rocks or slicing through obstacles hidden in mud. They are also more resistant to puncture when full of air.
Tire tread is measured in 32nds of an inch. New tread depth for the Discoverer STT tires is 20.5 (32nds). We averaged 6/32 inch of wear during the 18,286 miles accrued during the test (the rears used 1/32 inch more than the fronts). This left 2/32 inch for safety and the wear bars, which means a third of the available tread depth in 18,000 miles was used. Translation: you should expect approximately 55,000 miles for these tires when mounted on a similarly equipped Jeep.
Cooper's blend of synthetic rubber with other compounds contributes to the STT's long mileage and durability. The ride control and flexibility of the STT's radial construction make these tires an excellent choice for mud/sand/snow/rock traction-all of which (except for the snow) were encountered on this trip along the Mojave Road, a National Heritage Trail.
The bottom line is that they work and how!
