August 27, 2015

Buyer’s Guide to Trucks and SUVs: 4WD vs. 2WD vs. AWD

As pickup trucks and SUVs become more popular in Thailand, these segments attract new customers who previously only drove passenger cars such as sedans. Customers who are new to these segments usually cite the higher seating position, rugged design, increased cargo capacity and off-road capability as reasons for purchase.

Chevrolet Colorado High Country owner Boonlert Sudjaidaee from Nakorn Pathom Province said the premium pickuptruck has been very helpful in his work. “When my customers and employees come to my fish farm they have to drive a tough, steep road, and their cars often get stuck. So, I have to tow them. That’s why I need reliable 4WD truck. I tested the High Country and realized that Chevrolet’s 4WD is really good. When I drive up or down hill, it has systems that help me do it safely. Also, the suspension is firm and gives good grip.” Boonlert said.

Pickups, such as the Chevrolet Colorado, and truck-derived SUVs or PPVs, such as Trailblazer are available in 4WD (4x4)and 2WD (4x2) variants, while car-based SUVs, such as Chevrolet Captiva, are available in AWD variants. When shopping for a first truck or SUV, it is smart to know the differences between these systems to make the right choice.

4WD vehicles are popular with customers who need maximum traction and capability in off-road conditions.

4WD vehicles can drive power to all four wheels, typically using a two-speed transfer case with high-range (4x2 and 4x4Hi) and low-range (4x4 Low) for additional torque. The 4WD variants of Colorado and Trailblazer have a part-time 4x4 drivetrain that generally operate in rear-wheel-drive (RWD) until four-wheel traction is needed, such as in off-road conditions or on slippery pavement.

On full-time 4WD vehicles, all four wheels are driven all the time. The transfer case in the center of the transmission system decides how much torque is split between the front and rear wheels. Typically, more torque is sent to the rear. It changes to a 50/50 split in off-road and slippery conditions, where maximum traction is required. In full-time 4WD vehicles,the driver must still engage the low range (4x2) manually.

2WD vehicles use power driven to only two wheels, usually the rear wheels (RWD), and are a popular choice for customers who do not need the maximum capability offered by 4WD and do not expect to drive in extreme off-road conditions.

RWD vehicles can more effectively handle higher engine power and higher vehicle weights than front-wheel-drive vehicles such as passenger cars, which is why it’s still favored in large trucks, larger and very powerful performance vehicles,purpose-built race cars and law-enforcement vehicles designed for pursuit.

Under heavy cornering conditions, RWD vehicles generally tend to oversteer. It basically means the vehicle turning or steering more than commanded by the driver. In extreme situations, this may result in a slide or a spin. Oversteer is more difficult to control than understeer and; therefore, it is a more dangerous dynamic.

Not to be confused with 4WD, vehicles that have AWD use a full-time single-speed system that supplies power to all four wheels. AWD scores high with buyers who want excellent on-road capabilities with the added traction on grass, mud, sandor gravel in light, off-road conditions where a front- or rear-wheel-drive vehicle may get stuck. AWD vehicles tend to behave more like a FWD vehicle, in that they understeer when pushed beyond the limit.

Fuel economy can be improved by shifting torque to the front wheels when driving in normal conditions while greater traction can be achieved by automatically shifting torque back and forth during adverse driving conditions. The system works in cooperation with Active Torque on Demand system, which has the ability to increase torque delivery to individual wheels to increase stability. Generally, an AWD drivetrain operates as a FWD or RWD system – most are FWD, like the Captiva. An AWD system preemptively sends power to front and rear axles on every launch to prevent wheel slip and then reverts to FWD if no slip occurs. Power is transferred automatically via a single-speed transfer case (a transfer case connects to the transmission to split power between the front and rear wheels).

Source: Chevrolet Thailand via Chevrolet Philippines

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