Cooper Discoverer STT TEK3 Ultra High Performance Tire - 325/65R18 127N E2 "Armor-Tek3" Carcass Construction. The heavy duty carcass of the Discoverer STT is constructed of two radial polyester body plies and one angled polyester body ply to provide 3 full plies of protection for superior resistance to impact breaks and bruising. The shoulder tread lugs of the Discoverer STT are scalloped so that one section always has a clear shot at fresh ground for superb traction in soft surface applications and additional gripping power in off-road applications. Resistant Tread Compound Rim Flange Protector. A raised rim protector helps protect the wheel and tire from hazards in off-road driving conditions while enhancing the Discoverer STTs appearance. The new Discoverer STTs computer designed, non-directional tread employs a combination of features including deep buttress lugs, notched and scalloped shoulder lugs to create a bold, aggressive tire for tough off-road applications.