Tigercat achieves improved tractive effort and travel speeds with their new drive system.The EHS drive system consists of two variable displacement motors providing input into the transfer case. The front and rear output shafts are connected directly to the front and rear axles. The EHS is capable of providing the tractive effort of the deepest gear ratio available in Tigercat's standard transfer case, and the top speed of the shallowest gear ratio in the standard transfer case. This is made possible by using sophisticated computer logic and the ability to take one of the drive motors offline when high tractive effort is not required. When this occurs, all pump flow is directed to one hydraulic motor, increasing the travel speed and motor efficiency.
If conditions demand high tractive effort, both hydrostatic motors are working, and when tractive effort requirements are reduced (for example when travelling empty), all the pump flow is directed to one motor for higher travel speeds. Tigercat is offering EHS standard in the 610C and the new 615C. Source: http://www.tigercat.com/index.php/News-Items/new-ehs-skidder-drive.html