In 1985, Caterpillar expanded its revolutionary elevated sprocket undercarriage concept to its medium track-type tractor (MTTT) line with the launch of the H-Series models. Still unique to this day for the 130 to 350 hp (100 to 250 kW) dozer class, the high drive design conformed to the ground better, improving durability, serviceability, and performance compared to low-drive and oval track designs.

The Cat® D4H, D5H, D6H, and D7H dozer models were the first to feature the high drive design, and in 1987, the D8L model was added to the family. In addition to bringing many of the same large dozer advantages to the medium line, the elevated drive sprocket allowed movement of the front and rear track idlers. This helped to fine-tune machine balance and ground pressure for specific applications more easily than oval track machines. For the first time, variable pitch angle tilt (VPAT) blades were made available to high drive dozers with the D4H and D5H models for finishing jobs faster by grading at higher speeds.

Thirty-five years later, Caterpillar celebrates the unrivaled success of the elevated sprocket design in the medium dozer class by producing three commemorative 175,000 units in May 2020. “One of the original taglines to promote the early high drive tractors was ‘Beyond Known Capabilities,’ because these units set a new standard for efficiency, productivity and ease of operation,” says Wes Holm, chief engineer, Caterpillar medium tractor products. “With our next generation medium dozer line, which includes the new D5, D6, and D7 models, we continue to push these envelopes through adaptation of technology to drive productivity and efficiency to another level.” For more, visit