To 4WD or to not 4WD

When looking for a vehicle there never seems to be much deliberation about four-wheel or all-wheel drive systems. Either buyer’s expect them or they don’t. Often times a singular experience drives their decision to four-wheel-drive (4WD) or not to four-wheel drive. People who feel they need 4WD may have in the front of their minds a positive or negative experience that dictates their choice. Maybe they had a personal struggle in a snowstorm that left them physiologically scarred. Perhaps they were riding shotgun in a friend’s 4x4 pickup that confidently blew through a foot of white powder past a bunch of front wheel drive sedans that could barely drive ten feet without spinning out. With so much emotion from an experience like this it may be helpful to have some logic to balance it out.

Two-Wheel Drive (2WD)

Drivetrain configurations determine how and to which tires the engine’s power is transmitted. The tires’ grip or traction on the road is what generates motion and control. More traction equates to better on-road performance. The question is: “How much traction do we really need?” 

Traction is the friction with the ground that is used to propel a vehicle forward. Let’s say you are walking and you step on a banana peel and slip. The foot that steps on the banana is receiving the downward force of power from the leg but the banana cause that foot to slip and the power is moved in an unintended direction. The slippage may happen so fast the other leg can’t recover and down you go. If you are walking at moderate pace when you slip you may be able to compensate for the loss of balance but the faster you are walking or running the more difficult it is to recover from a slip. 

This same phenomenon occurs in driving a two-wheel drive (2WD) vehicle, either front- or rear-wheel drive. As the name implies only two-wheels either front or rear are set up to receive power and thus create traction. If one of the drive wheels encounters a patch of ice or snow it loses balance and the wheel with the most traction will push the car to slipping side and the driver will lose control. Front- wheel drive (FWD) and rear-wheel drive (RWD) cars will behave differently as they have different weight distributions and drive wheel locations. In a FWD vehicle the heavy weight of the engine bearing down over the front drive axles naturally produces more traction by exerting a force that helps keep the tires in closer contact with the road. Conversely RWD configurations have typically been more susceptible to slippage because less weight sits over the rear axle. 

Four-Wheel-Drive (4WD) / All-Wheel-Drive (AWD)

Four-wheel-drive (4WD) and all-wheel-drive (AWD) vehicles offer the potential of better traction because all four wheels can receive drive power. Imagine you had two extra legs in the banana slip incident. In addition to drawing the attention of scientist the two extra legs and feet would give you a greater opportunity to recover balance after one foot slips. Traditional 4WDs divide the torque between the front and rear axles at a set percentage, usually near a 50/50 split.  Some 4WD systems allow the driver to select 2WD or 4WD performance based on the driving conditions. This feature is being slowly replaced by AWD and variable 4WD systems that can alter the split in response to slippage. These systems are marketed as advanced, smart, intelligent, real-time or active systems but they all perform essentially the same function.

Pros and Cons of 4WD and AWD

4WD and AWD configurations enhance traction, control and stability in a multitude of driving situations. In low-traction situations they send power to all four wheels to maximize traction and minimize slippage. AWD and variable 4WD systems actual transfer power to the wheels with the most traction by quickly responding to any wheel slippage. However 4WD and AWD systems can add in upwards of $2000 to $4000 in cost to the bottom line of a vehicle. They also have lower fuel economy due to the fact they are heavier and slightly less efficient than 2WD systems. The challenge with 4WD is that the extra cost and weight is always there even when you do not need it. So when considering your next vehicle it would certainly be beneficial to understand your region’s climate and landscape. Areas that receive heavier snow and rain throughout the seasons may benefit from 4WD and AWD. However an area with a milder winter but a hilly topography may also warrant strong consideration of 4WD and AWD. Getting up a slick hill may be nearly impossible for some 2WD cars. Many local governments aren’t as equipped as others when it comes to snow and ice removal. Snowplows and salt trucks just aren’t as much a priority in Georgia as they are in Massachusetts. Living in an area with unpaved roads can get tricky with any kind of precipitation. Gravel and dirty can quickly transform to mud and puddles. 

Traction Control and Electronic Stability Control (ESC)

2WD vehicles equipped with computerized control enhancing equipment may be a less costly alternative to a 4WD or AWD vehicle. Traction Control and Electronic Stability Control (ESC) utilize the vehicle’s brake and engine control systems to counteract slippage and instability. Going back to the banana slip scenario the instant a foot begins to slip on the banana your nervous system would react by stopping the slipping foot or even slowing the both feet to give you a chance to recover before you get too far out of balance. Similarly traction control and ESC employ an array of wheel speed, vehicle speed, steering wheel and directional sensors to continuously monitor for wheel slippage or any unintended vehicle movement. Once identified theses systems brake the appropriate wheel or wheels and may even reduce power to the engine to bring the vehicle back under full control. The government has mandated that all new cars have ESC for the 2012 model year and beyond. And since the early 2000s ESC and traction control were standard or available on several model vehicles.

When shopping for that next ride match your personal situation and preferences to all of the great drivetrain and vehicle control options out there. If possible make sure your test drive includes some less than ideal road situations. And watch out for those banana peels too.