• What you should know about AWD, FWD, RWD, 4WD


    AWD, FWD, RWD, 4WD, full-time 4WD. So what do all those acronyms really mean?

    Knowing what type of drive system a vehicle is can allow a motorist to drive safely (and even faster) when taking those turns and straightaways. But with car makers following their own “acronyming” can sometimes confuse those who are not necessarily “gear heads.”

    For this issue, Fast Times will try to inform readers on what those acronyms really mean, even if car makers insist on their own labelling or “acronyming.”

    FWD – simply means front-wheel drive, or the front wheels propelling the vehicle. Front-wheel drive systems are more popular today because of their compact design and lesser use of parts; there is no need for that lengthy propeller shaft or the rear axle for vehicles that have their engines mounted at the front of the car.

    FWD thus allows car makers to lower production costs because lesser metal is used. Also, FWD makes for lesser weight, thus improving fuel economy (theoretically).

    The quirk of FWD cars is that most of them are prone to understeer, or the vehicle going outside the line of a curve when pushed hard. Theoretically along a sharp turn, a car that understeers can make you intrude into others’ space, making possible an offset collision with a vehicle coming from the other direction.

    RWD – simply means rear-wheel drive. While there are cars with engines that are mounted at the rear (as in the case of a big number of sports cars), most RWD vehicles have their engines mounted at the front. This arrangement makes necessary a propeller shaft and a rear axle, thus increasing the overall weight of a vehicle. No wonder, RWD vehicles are generally more expensive than FWD cars.

    The weight of the propeller shaft and the rear axle can be more than two times that of the axle assembly of FWD cars. In SUVs, the solid axle can weigh as much or more than the engine.

    The quirk of most RWD cars is that they are prone to oversteer, or the vehicle entering a turn sharply if not handled properly or pushed hard into a turn.

    4WD – simply means four-wheel drive and is generally not full-time like all-wheel drive or AWD. This type of system is popular with SUVs that are also meant to be driven off-road, and usually have a normal and low setting for taking really nasty or challenging roads that are not paved, have loose surfaces or muddy.

    Most 4WD systems are also RWD, and shifting from RWD to 4WD can be done by flicking switches or turning dials given the electronic systems developed by car makers. Switching from high to low also requires the flick of a switch or turning the dial.

    FWD vehicles that can be switched to 4WD are still rare. Meanwhile, SUVs that have either FWD or RWD are labeled at 4×2 standing for two-wheel drive.

    All-wheel drive and four-wheel drive differentiated
    AWD – simply means all-wheel drive and is also labelled as full-time 4WD. But full-time 4WD should aptly be labelled as AWD. While there are SUVs that have AWD, a good number of high-performance vehicles bearing the Nissan, Subaru, Audi, Porsche and Lamborghini brands, among others, have AWD for one simple reason: having power on all four wheels gives the best grip on the road.

    Of course, AWD systems are complicated and are also governed or co-governed by complex electronic systems. The drawback of AWD systems is increased fuel consumption, because the vehicle is heavier and powering all four wheels needs gobs of torque and lots of horsepower.

    There are also AWD systems for SUVs that have the normal and low setting found in traditional 4WD systems.

    There are cars whose AWD systems that can be turned off for the vehicle to be powered either by the front wheels (FWD) or rear wheels (RWD). This can be aptly called part-time AWD and should not be confused with 4WD that have normal and low settings.

    AWD is supposed to provide neutral steering behavior – or the absence of both oversteer and understeer.

    Which is best
    For normal city and highway driving, there is little difference between FWD, RWD, AWD and 4WD. But for driving under special conditions, each drive system has its virtues.

    FWD cars, because of their lighter weight, can help achieve better fuel consumption (unless you are a mad or pedal-to-the-metal driver). RWD still finds favor for larger vehicles like vans, trucks and SUVs, because fitting a large engine with an FWD system is a complicated design that can increase the cost of a vehicle.

    AWD is mostly favored for high-performance driving. But then, most high-performance muscle cars from the United States are RWD, and Formula One and IndyCar open-wheel race cars, considered the fastest in the planet using internal combustion engines, are also RWD.

    One reason why Formula One and IndyCar racing machines are only RWD (instead of AWD) is that motor sports is also about driving skills, not about complicated machines. Just imagine if all race cars had AWD and various electronic interventions that will make it easier for even an average Joe to propel a car past 400 mph?

    There are also electric cars that offer AWD and hybrids that have electric motors powering the front wheels to complement the rear wheels powered by the vehicle’s internal combustion engine. One advantage of electric motors is their compactness, which allows car makers to mount a number of them to power both the front and rear wheels.

    While FWD, RWD and AWD have their own steering behaviors, there is this view that a skilled driver who knows the three steering behaviors can still track a car safely into a turn by doing the following: always slow down or brake along a straight line; shift to a lower gear before entering the turn; take good hold of the steering wheel with two hands when maneuvering the vehicle into a turn; and apply power when the vehicle is pointed toward its intended directions. Of course, there are “gifted drivers” who know how to alter that procedure and still take their vehicle fast into a turn with almost total control (well, that is worth discussing in another article).

    Add-on technologies
    Realizing that motorists cannot always judge road conditions ahead accurately, car makers have installed traction control systems to control power on the wheels that should result in minimizing or arresting behaviors caused by understeer or oversteer.

    Then there’s torque vectoring, which distributes torque to the wheels depending on road conditions. This is also supposed to minimize or arrest behavior related to understeer or oversteer.

    Leading car makers are also making four-wheel steering a feature in a number of their high-end vehicles. The technology allows the rear wheels to either turn in the opposite or same direction as the front wheels, thereby improving maneuverability.

    Electric steering has also made it possible for car makers to set modes for different speeds, or making the steering more taut for higher speeds and lighter for lower speeds. This helps drivers from making just the right steering inputs based on speed.

    More technologies to make vehicles handle more brilliantly are surely being developed by car makers, which could one day negate the usual characteristics of FWD, RWD, AWD and full-time RWD, or at least part of it. That is definitely good news for motorists.


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