The Victoria Napolitano Bookstore THE DRIVING COMPANY WORKBOOK

TORQUE, TRACTION, AND THE 4WD SYSTEM Understanding the relationship between torque and traction is necessary to effectively drive in a variety of off-road conditions. “Torque” is the amount of twisting force supplied to the wheels. “Traction” is the amount of friction between the tire and the road surface. If more torque is applied to a wheel than the amount of friction present between the tire and the road surface, then the wheel will lose traction and spin. The differential allows the wheels to turn at dif- ferent speeds and equalizes the torque between the wheels. This can be detrimental in off-road situations where one wheel has traction and one wheel starts to slip. When one wheel on an axle loses traction, less torque is required to make it turn. Because the differential equalizes the torque, less torque will then be present at the wheel with better traction. The torque present at the wheel with traction may not be enough to move the vehicle. This is where 4WD comes in. On a part-time 4WD system, there is a transfer case that allows torque to be sent to both axles. The drive shaft going to the front differential and the drive shaft going to the rear differential are rotating at the same number of revolutions per minute (RPMs). The differentials then split the RPMs between the two wheels. The sum total RPMs of the wheels on the front axle is the same as the sum total on the rear axle. If one wheel loses traction, then you will still have torque present at the other wheel on the same axle because the wheels on the axle must turn at the same total RPMs as the other axle. When you turn the vehicle, the wheels will start turning at different RPMs. Whichever wheel has the least amount of traction will be dragged or pushed across the ground due to this equa- tion. You can hear this happening when off- road, but if you are on pavement with a lot of traction it will be very difficult to turn as you fight against these forces. TheDrivingCompany.com 2

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