The AT81 and AT81RC (Reinforced Construction) and AT81EX ( Endurocross) tires offer more all-around performance plus higher levels of ruggedness for off-road racing and riding.AT81 rear tread block shape and distribution plus flexible knobs help the tire The AT81 and AT81RC (Reinforced Construction) and AT81EX ( Endurocross) tires offer more all-around performance plus higher levels of ruggedness for off-road racing and riding.AT81 rear tread block shape and distribution plus flexible knobs help the tire