PART-TIME FOUR-WHEEL DRIVE Part-time four-wheel drive is the most common type of all wheel drive. It usually operates only in two-wheel drive mode and it can be switched to all-wheel drive whenever the situation requires. By employing a center differential or a transfer box, these types of all-wheel drive systems can transfer power to either the front only, rear or to all the drive wheels, depending on the driver's wishes. On older designs, the all-wheel drive mode had to be manually engaged and the vehicle had to be stopped in order for the (usually front) wheel hubs to be locked, but it can now be done from the inside of the vehicle and on some vehicles even while they're moving. Permanent Four-Wheel drive PERMANENT FOUR-WHEEL DRIVE Permanent four-wheel drive systems send power to all four wheels in a continuous manner. There is no need for the driver to engage two or four-wheels drive mode, since all of the wheels are always p