Nearly every major automaker has adapted some form of all-wheel driveline to one or more of their product lines. Ford uses Control-Trac, Control-Trac II, and Intelligent-Trac, General Motors the Auto-Trac, BMW has the X-Drive, and Mercedes-Benz equips their luxurious models with the 4Matic, and this is only to mention a handful.
To the average consumer, choosing the right driveline can get really confusing. So, how do you determine which driveline is right for you? Front-wheel drive, rear-wheel drive, on demand four-wheel drive, or all-wheel drive; which one best meets your needs?
Driving habits, weather conditions, and the geographic location must be considered prior to making your purchase. Making the correct choice can mean the difference between enjoying years of dependable service and getting stuck with a vehicle which consistently comes up short. This three-part guide is for potential new and used car buyers with an emphasis on helping you to choose the right driveline.
Part three of this guide, on drivelines, will cover all-wheel drive systems. Check out Part 1, which deals with two-wheel drive (both front and rear) vehicles, as well as Part-2 about on-demand four-wheel drive systems.
All-Wheel Drive
All-wheel drive systems vary from on-demand four-wheel drive in several ways:
- All-wheel drive typically signifies a full-time four wheel drive system; on-demand utilizes a system which may be converted from two to four-wheel drive (and back) by the vehicle operator.
- On-demand four-wheel drive vehicles are very similar from one manufacturer to the other; all-wheel drive systems vary, to a great degree, one manufacturer from another.
The Control-Trac (I & II) and the Intelligent-Trac, designed by Borg-Warner, feature a design which closely resembles that of an on-demand four-wheel drive unit. Of course, the key difference would be the all-wheel drive system’s ability to effectively utilize traction from all four wheels at highway speeds and on paved surfaces. Control-Trac and Intelligent-Trac systems are commonly referred to as automatic all-wheel drive systems. Data from the four vehicle speed sensors is calculated by the Powertrain Control Module (PCM), which controls the all-wheel drive system. This system uses a conventional rear differential, with constant velocity axles, and an electronically controlled dual-clutch differential in the front. Traction is modified between the four wheels using vehicle speed inputs from the four corners, making a rolling comparison, and applying the required amount of torque to the designated wheel.
GM uses a similar design to Ford’s Intelligent-Trac for their mid-sized SUVs and some pickup trucks. The Auto-Trac system was used in many S-10 and S-10 Blazer vehicles.
Many Jeep vehicles and Dodge pickup trucks use the Chrysler Command-Trac a selectable automatic all-wheel drive system. This system also bears striking similarities to the Intelligent-Trac system; the vehicle operator may choose from an automatic four-wheel drive option or manually choose full-time four-wheel drive in high and low gear configurations.
BMW
The xDrive all-wheel drive classification refers to BMW’s automatically adjustable, electronically controlled full-time four-wheel drive scheme. It uses data from the anti-lock braking system and the dynamic stability control system to calculate and respond to traction requirements at all-four wheels. BMW uses a dual-clutch gearbox to transfer power to the front and rear wheels according to the degree of variation between front and rear wheel speed, as well as left and right wheel speed sensors.
The 4Matic four-wheel drive system is used by Mercedes-Benz in their coupes, sedans and SUV models. It also uses vehicle speed sensors to determine how much power to apply to each wheel in an effort to maintain efficient traction and vehicle speed and stability.
All-wheel drive vehicle are excellent for areas where severe weather is common. Heavy snow and rain are easily and effortlessly managed by this type of driveline. Many performance driving enthusiasts also prefer an all-wheel drive vehicle for stability and traction; however, serious racing aficionados balk at the added bulk of the front axles, transfer case, and drive-shafts.
