4WD is the abbreviation for 4-Wheel Drive and drives all four tires using transfer, etc. There are two types of 4WD, full-time 4WD and part-time 4WD. 4WD vehicles can also be classified into those based on FF (Front-engine, Front-wheel-drive) and those based on FR (Front-engine, Rear-wheel-drive). Furthermore, 4WD vehicles can also be classified into those for driving off-road and those for driving on-road.
1. Operation of differential
The vehicle uses the differential to absorb the rotational difference during cornering. With full-time 4WD, there is a center differential in addition to the front differential and the rear differential in order to absorb the rotational difference between the front and rear wheels. Providing three different differentials makes smooth driving possible by ensuring the equal transmission of power to all four wheels, even during cornering – this is the major advantage of full-time 4WD.
When part-time 4WD vehicles, which do not have a differential to absorb the rotational difference between the front and rear wheels, turn sharply in the 4WD mode, the tight corner braking phenomenon occurs and smooth cornering becomes impossible. For this reason, with part-time 4WD, switching between 2WD and 4WD in response to driving conditions becomes necessary.
2. Tires and installing tire chains
All four tires mounted on a 4WD vehicle must be of the same size and type. If the front and rear tires are of different diameters, the center differential will have to operate at all times, even on a straight, level road. And if the diameters of the left and right tires are different, the front or rear differential will have to operate at all times (depending on whether the tires that are of different sizes are in the front or rear). Full-time 4WD offers outstanding drive-through performance on rough and snowy roads, but in some cases, it is necessary to install tire chains. At such times, the following point should be considered. When a 4WD vehicle is based on an FF model, tire chains should be mounted on the front tires. When the 4WD vehicle is based on an FR model, the tire chains should be mounted on the rear tires. If a mistake is made, the tire chains could hit the body and damage it, so exercise caution at all times.
Types of 4WD
4WD can be classified into the following types according to differences in the drive type and control.
1. Part-time 4WD
With this type of 4WD system, the driver switches between 2WD and 4WD in accordance with road conditions by the transfer. Ordinarily, the vehicle is driven in 2WD, and 4WD is used for rough roads and snowy roads, etc. However, because the part-time 4WD system has the front and rear drive trains connected directly together, the tight corner braking phenomenon occurs during cornering, and the vehicle cannot be turned smoothly. For this reason, it is necessary to switch from 4WD to 2WD when driving on ordinary roads.
2. Full-time 4WD
The vehicle which can be used at all times under all road conditions and driving conditions, from ordinary roads to rough roads to low coefficient-of-friction roads, is full-time 4WD. Also, the full-time 4WD vehicles are equipped with the center differential.
3. V-Flex full-time
4WD V-Flex full-time 4WD system enables the vehicle to operate practically in the 2WD mode during normal travel when there is almost no rotational difference between the front and rear wheels. When a rotational difference is created between the front and rear wheels, such as during cornering or driving on a snowy road, this system transmits the drive force to the rear wheels. Thus, it ensures stable maneuverability while driving in various roads and driving conditions.