Ken Brubaker
Senior Editor, Four Wheeler
Recently, we were invited to the Cooper Tire & Vehicle Test Center (CTVTC) in Pearsall, Texas, to see the all-new Discoverer A/T3 and S/T MAXX tires.
The CTVTC was built in 1999 at a cost of over $13 million and it encompasses 1,000 acres. It is home to a number of testing areas, including many that apply to us off-highway fans. The Off Road Course includes just about every type of obstacle one could encounter off-highway, including a rock garden, rock hillclimb, mud, silt, and gravel. We tested the new A/T3 in the mud as well as on the 14-acre Wet Vehicle Dynamics Assessment Pad (commonly known as a skidpad). We were able to test the S/T MAXX on almost the entire Off Road Course in addition to a wet concrete hillclimb.
The all-terrain A/T3 and the mud and snow-rated S/T MAXX are the newest products to be rolled out by Cooper in the Discoverer line, which has a lengthy history of over 30 years. During the design phase of the tires, Cooper set out to identify what the average buyer for each type tire wants and then they integrated these features into the tires. Here’s what they came up with.
Discoverer A/T3
Overview: The A/T3 features a five-rib design, and the tread elements are coupled together to provide stability and confident on-road handling. The center rib is divided, and Cooper says that this improves off-highway traction without sacrificing on-road performance. The tire includes a couple of features designed to provide reliable soft-surface traction. One is the aggressive shoulder and the other is the wide “Chevron”-style circumferential grooves. Those grooves also help the tire clean itself when off-highway. The tire’s thin-gauge, zig-zag-shaped siping helps to accomplish a few things, including the reduction of stone retention, and it improves the stability of the tread blocks. And speaking of stone retention, the tire was designed with lateral groove protectors that have serrated steps to reduce the chance of stone retention and stone drilling. Another noteworthy feature of the tire is that the tread compound is a silica-based formula, which is a key to the tires wet weather performance.
Behind the wheel: The silica-based tread formula demonstrated its benefits on the Wet Vehicle Dynamics Assessment Pad, which contained a 2/3-mile, cone-lined course designed by Cooper. The course contained gradual and sharp turns, simulated lane changes, and areas to test acceleration and deceleration. We drove three identical Chevy Silverado pickup trucks, two fitted with competitors’ tires and the other with the Cooper Discoverer A/T3. When driven back-to-back, it was clear that the A/T3 had the upper hand in the wet stuff. The silica-based tread formula gave the tires a traction advantage we could feel, and the siping and design of the tread blocks were confidence-inspiring as we pushed the truck hard through the wet course. The improvement was illustrated by the fact that we averaged faster lap times using the Cooper Discoverer A/T3 than the other two sets of tires. We also had the opportunity to immerse the A/T3 in Cooper’s Mud Traction Area, which is a continuously-watered, 500x150-foot mud hole. We didn’t expect much out of the Cooper Discoverer A/T3 here—after all, it’s an all-terrain tire, not a mud-terrain. Imagine our surprise when the Cooper Discoverer A/T3 showed itself to be amazingly capable in the goo. We drove an A/T3-equipped Jeep Wrangler TJ on the course at length and were impressed by the tire’s ability to clean itself and get a fresh bite with each rotation.
Bottom Line: If you need an all-terrain that really does excel in all terrains, the A/T3 is worth a look. There are many neat ideas integrated into this tire. The A/T3 is slated to replace the Discoverer AT/R, and by the time you read this it will be available in 31 light truck sizes and 30 P-metric sizes with a 55,000-mile warranty.
»The Details
Tire: Cooper Discoverer A/T3
Size: LT265/70R17
Type: Radial
Load range: E
Max load (lb): 3,195 (single), 2,910 (dual)
Sidewall construction: 2-ply poly
Tread construction: 1-ply nylon, 2-ply steel, 2-ply poly
Approved rim width: 7.0-8.5
Tread depth (in): 16.5⁄32
Tread width (in): 10.9
Section width (in): 8.5
Overall diameter (in): 31.6
Static loaded radius (in): N/A
Revolutions per mile: 659
Weight (lb): 50
Discoverer S/T MAXX
Overview: The S/T MAXX features Cooper’s three-ply “Armor-Tek3” carcass construction, which means it has two normal radial plies run at 90 degrees from the bead and a third Armor-Tek3 protective ply at a unique angle to the two normal radial plies. Cooper says this arrangement adds strength and durability to the tire. It has a proprietary blended natural rubber and silica-based tread compound that offers great wet traction and excellent cut and chip resistance. It has a hybrid 4-5 rib tread design that helps create a quiet ride and positive grip, and it features stone ejector ribs, dual-draft walls, and non-parallel groove walls that combine to help resist stone drilling and retention. The outside edge of the tire features an enhanced buttress design that serves several purposes. It provides additional traction, helps resist abrasion, and helps prevent lug tearing. The tire also features a rut guard rib and rim protector.
Behind the wheel: We began our test of the S/T MAXX on the 100x16-foot Rock Crawl/Sidewall Durability Course. This limestone boulder course is designed to demonstrate low-speed rock traction and resistance to tire bruising, tread cutting/chipping and sidewall puncture. The tires were set at 15 psi and mounted on a Jeep Cherokee XJ. One of the first things we noticed was that the tire exhibited a noteworthy ability to conform to the rocks and pull the XJ along. And thanks to the aggressive outer edge of the tire, we were able to plant the shoulder on boulders numerous times without slipping off. We also appreciated the rugged construction, which decreased the likelihood of sidewall damage during these maneuvers. Next up was the Hill Climb area. Here, we drove up two 30-foot-long climbs that have an angle of 30 degrees with 1/10 inch of water flowing over the surface. These areas are designed to test the tire’s compound and tread pattern effectiveness. The first was a smooth concrete surface, and we expected that the more aggressive lug design would contribute to tire slippage. Conversely, the tire stuck to the wet concrete like glue and carried us to the top numerous times (even backwards) with no wheelspin. The other climb was a brushed concrete surface with embedded rock. This was a very challenging surface, but the tire did well as the compound and tread combined to latch onto the mix of surfaces and pull us to the top. Finally, we took the tire out to the 1.5-mile-long Trail Ride Course, which contained a variety of conditions including mud and water. Once again, we were impressed by the tire’s ability in all of those settings. Following an afternoon of crawling on a number of obstacles including sharp rocks, the S/T MAXX didn’t show any signs of “chunking” and the lugs were intact.
Bottom line: If you’re looking for a tire that can handle rougher terrain, but you also want a tire that’s designed to be quiet on-road with excellent wet weather traction, the S/T MAXX may be what you’re looking for. This tire will eventually replace the Discoverer S/T-C and selected sizes of the S/T. It is currently available in eight light truck sizes with more coming in early 2012. fw
»The Details
Tire: Cooper Discoverer S/T MAXX
Size: LT265/70R17
Type: Radial
Load range: E
Max load (lb): 3,195 (single), 2,910 (dual)
Sidewall construction: 3-ply poly
Tread construction: 1-ply nylon, 2-ply steel, 2-ply poly
Approved rim width (in): 7-8.5
Tread depth (in): 18.5⁄32
Tread width (in): 8.7
Section width (in): 10.7
Overall diameter (in): 31.8
Static loaded radius (in): N/A
Revolutions per mile: 652
Weight (lb): 55
