WASHWORKS® Vehicle Product Information
Vehicle Product Information - Vehicle Drive Systems
When automobiles first came on the scene, they were all two-wheel (2WD). Power from the engine (in the form of torque) was sent via a drive shaft or chain to two of the vehicle's four wheels. These were commonly the rear wheels, which pushed the auto along the road.
Front-wheel drive, in which the vehicle is pulled along by the front wheels, wasn't far behind. In 1898, Latil, a French company, began making front-wheel drive units. And just four years later, the Dutch introduced the Spyker, which sported fulltime four-wheel drive, also known as All-Wheel Drive (AWD).
So just what is the difference, and which one is best? The answer depends upon how, and where you plan to drive your vehicle.
If you're going straight from Point A to Point B, never leaving dry, flat, well-maintained pavement, then 2WD makes perfect sense. Trillions of miles have been traveled in that mode. But roads are not always straight, flat nor dry. That's when 4WD and AWD became alternatives.
 |
Temporary power up front + full-time power in back = 4WD
Most automakers agree that the term "four-wheel drive" usually indicates a part-time system, meant only for use in low-traction conditions, such as off-road or snow or ice. It is engaged manually, when the driver decides. In its simplest form, a four-wheel drive vehicle has the ability to send power to all four wheels. The ideal system will send exactly the right amount of torque to each wheel to prevent tire slip. And traction is what its all about.
In a typical 4WD system, power from the engine feeds into a transfer case, which, in turn, is connected to two drive shafts - -one that supplies torque to the front tire on a temporary basis, while the other drives the rear wheel full-time. This transfer case locks the two drive shafts together so the wheels spin at the same rate. This means that the outside tires must slip laterally when the car goes around a turn. While great in sand, snow or in ice where this sideways scraping can occur safely, you definitely don't want to drive around town or along the highway on a sunny day with 4WD engaged. Because not only will the steering become Dangerously jerky as the tires slide and grab, you'll also wind up shelling out a lot of money on replacement tires and drive-train repairs. Which brings us around to AWD (again)!
Full-time power up front + full time power in back = AWD
When we talk about all-wheel drive, we're referring to vehicles that have permanently four-wheel drive capability. In other words, it can't be shut off - unlike 4WD. And this makes it a good thing. Because while AWD continually monitors wheel slippage (going forward) and transfers power to the wheel where it's needed most under poor road conditions, it also provides exceptional control and traction when driving on hard, dry pavement or icy roads. You get the best of both worlds.
So how is this possible? It all has to do with the transfer case that splits the engine's power between front and rear wheels.
Recall that in 4WD, the transfer case locks front and rear wheels together so that they all turn at the same rate. Ideal for slogging across a muddy streambed, not so good for turning corners on a dry road. In AWD however, the transfer case contains either a fluid or mechanical device that allows for a speed difference between the front and rear wheels.
And what about "traction control"?
A luxury safety feature on many upscale cars, such as the Acura TL Premium, Toyota's Avalon XLS and the Nissan Altima 3.5, is an item referred to as "traction control" or "vehicle skid control." This feature monitors a car's steering angle, g-loads and yaw (sideways movement), and uses a car's Anti-lock Brake System (ABS) to selectively apply braking power to wheels that start to skid. Some vehicles also decrease engine speed to help keep the vehicle safety under control. While a nice feature to have, traction control should not be confused with AWD or 4WD
So what's it going to be?
Again, It all depends upon where you roam. If you play in deep sand or have a loose dirt trail, then 4WD is probably your best choice. If you're not so adventurous, but still want superior traction and control over the widest range of road conditions, then AWD is definitely the way.
Reprint from Automotive Showcase Magazine