This allows the trucks to start moving from a standstill with heavy loads in difficult forestry conditions.
The system is unique for series-produced heavy trucks. This new version of I-Shift makes it possible to add up to two new crawler gears. With the new crawler gears, the truck can drive at speeds as low as 0.5 to 2 km/hr (0.3 to 1.2 miles/hr). The improved driveability and startability with the new crawler gears makes the driver's job far easier when operating in difficult terrain on slippery surfaces with heavy loads. For transporters carrying out heavy transport operations on demanding surfaces as well as regular highway driving, such is often the case in forestry; the crawler gears also offer considerable flexibility and the possibility of improved fuel economy. Depending on the application, I-Shift is available with one or two forward crawler gears, and with or without two reverse crawler gears. Reverse crawler gears make it possible to reverse extremely slowly, which is a major advantage when reversing requires high accuracy.
The crawler gears are integrated into the I-Shift transmission. In order to handle the high loads involved, several components are made of high-strength materials. The gearbox is 12 cm longer than a conventional I-Shift unit. The I-Shift with crawler gears is available for Volvo Trucks' 13- and 16-litre engines in the Volvo FM, Volvo FMX, Volvo FH and Volvo FH16 series. In a gearbox with one crawler gear the ratio is 19:1 in a direct-drive gearbox, or 17:1 in an overdrive gearbox. The ratio of the lowest gear in a regular I-Shift direct-drive gearbox is 15:1. In a direct-drive or an overdrive gearbox with two crawler gears the lowest ratio is 32:1. The ratio of the lowest reverse gear is 37:1 in a direct-drive gearbox. Source: http://www.volvotrucks.com/trucks/global/en-gb/newsmedia/pressreleases/Pages/pressreleases.aspx?pubId=20165