Four-wheel drive is not as simple as it sounds. There are many factors involved which make a four-wheel drive system incredibly complex, and this article is meant to give you an overview on the basics of the four-wheel drive technology. First of all, there is more than one type of four-wheel drive. When a manufacturer says that a car has four-wheel drive, it does not necessarily mean that that vehicle is always in the four-wheel drive mode. Generally, this means that the vehicle has a part-time system. The other type of four-wheel drive is all-wheel drive, also called full-time four-wheel drive. In this system, the vehicle is permanently in four-wheel drive. The former type generally meant for use in low-traction, such as in ice or snow, while the latter type is always on and meant to function in all conditions. Both of these systems can be judged using the same criteria, as the best system will send the correct amount of torque to each wheel, which is the most torque that can be sent to that wheel without causing it to slip. To understand four-wheel drive, a basic understanding of torque, traction, and wheel slip is required: -Torque is the force that the engine produces which moves your car. The torque of an engine is also multiplied and split up by the gears in your transmission and differentials between the wheels. -Traction is the maximum force that your tire can produce on the ground. Traction is affected by three things, the weight pressing on the tire (the more weight, the more traction), the coefficient of friction (basically the amount of friction holding two surfaces together), and wheel slip. -Wheel slip happens when the amount of force, in this case torque, applied to a tire exceeds the amount of traction, causing the wheel to slip against the ground. Most of the time people do not even come close to exceeding the available traction on the surface that they are driving on, but in low traction situations, such as off-road driving or driving on snow and ice, four-wheel drive becomes very useful. The value of four-wheel drives is easy to understand. Basically, since you are driving four wheels instead of two, the amount of force the tires apply to the ground is doubled, making it easier to make a vehicle move. That’s why four-wheel drive shines in situations in which the amount of available traction is reduced. One basic type of four- drive system works like this: The vehicle is generally rear-wheel drive. The engine and the transmission are hooked up to a transfer case, which is basically a device that hooks up to two driveshafts, which are what indirectly spin the wheels. One of the driveshafts hooks up to the front axle, while the other is hooked up to the rear axle. When four-wheel drive is turned on, the transfer lock locks both driveshafts to each other, making sure each one receives half the torque produced by the engine. This ensures that each tire receives the same amount of torque and creating a basic four-wheel drive system. Unfortunately, there are two major drawbacks to this type of four-wheel drive. It cannot be used on a regular road because because of how the transfer case works. Since it forces all tires to spin at the same speed, it creates wheel slip on turns. (Normally, during a turn, all the tires are spinning at different speeds due to the the dual nature of the forces being exerted on all the tires.) The second drawback is that since the torque is split evenly between the two wheels on axle, if one of those wheels comes of the ground or hits a slippery surface, the torque of the other wheel drops to the same amount as the one that lost it’s traction. Because of these drawbacks, most newer four-wheel drive systems come with innovations that improve upon this basic system. There are many other four-wheel system vehicles currently on the market, and hopefully you will now understand more about what makes them work, and how to use them. Four-wheel drive isn’t perfect, but it is an interesting and complex innovation used in many vehicles today. Category:Home › Autos • Will the trend toward economy-size car models lead Americans back to buying smaller-sized cars? — part 2 • You should never use after-market auto parts when maintaining or fixing your car • Should a new car be rust-proofed? • Will the trend toward economy-size car models lead Americans back to buying smaller-sized cars? — part 1 • Five safest cars in North America • How to ensure your teen drives safely after getting a license • Pros and cons of using an hydrogen generator for your car • DIY automotive maintenance: How to change the oil