Abstract: A tread belt drive system for heavy mobile equipment includes an endless tread belt made up of a plurality of identical links joined together by link connecting pins. Each of the links has a ground engaging bottom and a top having a cog, or cog portion, positioned medially of the link ends, which cog has fore and aft driving surfaces. A pair of longitudinally extending tumbler rim and roller engaging surfaces which extend above the cog are positioned on the top of the link, one on each side of the cog. The links have fore and aft pin connections with the pin center below the engaging surfaces in alignment with the driving surfaces. The drive system also includes rollers which support the weight of the equipment and drive and idler tumbers each having a rim and teeth.