T I D B I T S    F E A T U R E
October 2001
By Jason Ang
Photos Courtesy of Mercedes-Benz, Toyota, Peugeot, Subaru, Porsche, Honda, Ford
Originally Published October 2001 Issue

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Are four driven wheels really better than two?  Manufacturers would have us believe so, not the least reason is that four-wheel vehicles can be more profitable than two-wheel drives.  A slew of marketing imagery from companies like Land Rover and Mitsubishi has given the four-wheel drive (4wd) vehicle an image of go-anywhere invincibility.  However, not all four-wheel drive systems are born equal, so we’ll show you some of the basics of 4wd, the benefits and disadvantages of having 4wd, and what to look for in a four-wheel drive vehicle. 

The idea behind 4-wheel drive systems is simple: by turning four wheels instead of two,  a vehicle can continue to propel itself forward even if two wheels lose their grip.  First of all, any 4wd system needs to have three basic components: a transfer case, an two differentials: one between the two front wheels, and the other between the rears.  

The transfer case divides the turning force from the engine, known as torque, and sends it to front and rear differentials.  The front and rear differentials then send the torque to each of the drive wheels. The differentials also allow a difference of speed between the left and right wheels, such as when the vehicle is turning.  When a vehicle turns, the outside wheel goes faster than the inside wheel because it’s following a larger-radius circle.  Most vehicles also have a center differential that allow for a speed difference between the front and rear wheels. 

Four-wheel drive used to be a feature only of military vehicles and large pickup trucks.  Audi was the first automaker to successfully introduce four-wheel drive in a car not with the intention for the owner to take it off-road, but simply to improve its roadholding characteristics.  They gave it the system the brand name Quattro, and indeed they branded the car itself Quattro.   “All-wheel drive” was coined as a marketing term to denote full-time 4wd, usually for improved roadholding instead of off-roading.  Many cars are now available with four-wheel drive, described variously as Quattro, Full-Time, Real-Time, All-Trac, etc.  There are two main types of four-wheel drive systems: part-time and full-time.

There are a lot of applications and uses of all-wheel drive as there are ways to make it more technologically advanced. The M-class uses its traction control to regulate the power giving the M-class good off-roading ability.

Unstoppable vehicles such as the original Land Cruiser shows the traditional use of all-wheel drive: safari hunting.

A more unconventional use of all-wheel drive must be its use in road cars to improve traction. Rally cars such as the Subaru Impreza uses all-wheel drive to dominate the competition in the WRC.

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