A tread for a pneumatic tire includes a first circumferentially continuous groove, a second circumferentially continuous groove, a central rib interposed between the two circumferentially continuous grooves and extending continuously around a circumference of the tread, a first circumferentially extending shoulder rib disposed laterally outside of the first circumferentially continuous groove, and a second circumferentially extending shoulder rib disposed laterally outside of the second circumferentially continuous groove. The central rib has a plurality of circumferentially spaced sipes arranged in a first circumferential row and a second circumferential row. The sipes of the first row originate at the first circumferentially continuous groove and the sipes of the second row originate at the second circumferentially continuous groove. The sipes of both the first and second rows extend axially inward to a circumferentially extending and continuous variable center groove. The variable center groove has a minimum circumferentially extending opening at a radially outermost portion. As the tread wears and the radially outermost portion of the tread moves radially inward, the circumferentially extending opening of the variable center groove widens to a maximum circumferentially extending opening greater than the minimum circumferentially extending opening.