It's kinda funny how so many people confuse all-wheel drive and four-wheel drive. Even the well-meaning marketing teams of manufacturers get the terms confused. Plus there's not even an international standard, so people in Britain use 4WD and AWD interchangeably, while here in the US they represent very different systems. But never mind all that -- most people just have absolutely no f*cking clue what any acronym ending in "WD" means.
For the vehicularly illiterate among you, there are basically four types of drivetrain layouts that harness the power from your car's engine and transfer it to your tires: FWD, AWD, 4WD, and RWD. Each one has its benefits and drawbacks. This isn't about what's wrong or what's right (cough, RWD, cough); just think of this as a handy guide to the unknown.
Rear-wheel drive (RWD)
First up, we have the oldest, the most tried and true, and by far the most beloved to car enthusiasts the world over: rear-wheel drive. Here, the rear wheels do all the pushing, leaving the front wheels to do the turning. When you think about what that means for the tires, the reason it’s such a good set-up for performance is obvious. Tires only have a limited amount of traction, so letting the rear tires focus purely on acceleration while the front tires focus purely on turning allows for the most efficient use of both sets.
Yes, there are drawbacks, like getting stuck in snow without much weight in back to push on the tires for added traction, but in the vast majority of situations, RWD remains king.
Front-wheel drive (FWD)
FWD is the most common drivetrain layout, and it's pretty self-explanatory: with the exception of braking, the rear tires are mostly along for the ride in a FWD vehicle, while the fronts do almost everything. In cars with lots of power, the wheels are sometimes pulled to the left or right by the sheer torque of the engine. This is something called torque steer, and if you floor your car and pay very close attention to the steering wheel, there’s a good chance you’ll feel it in your car. Sure, with modern engineering, some FWD vehicles are quite good.
FWD offers some advantages over RWD in snow, since the weight of the engine pushes down on the wheels, but in normal conditions it’s still a compromised set-up from a physics standpoint.
Why does it exist in the first place, and why is it so popular? Well, in the beginning, it was cheap. It’s far easier for a manufacturer to assemble a FWD engine/transmission combo and simply load it into a car on the assembly line, whereas the other drivetrains require a special tunnel running through the center of the car. It’s also lighter, which means better fuel economy -- during FWD’s rise to prominence in the years surrounding the gas crisis, that was kind of a big deal.
All-wheel drive (AWD)
So, on paper, AWD and 4WD both mean that all four wheels get power, and like I said, many parts of the world use the terms interchangeably. The difference is that AWD uses a specialized mechanism in the center of the car that distributes the power to both the front and rear, sometimes equally and sometimes biased towards one end or the other. This allows you to accelerate better, and when you're driving in conditions like ice or dirt, you can also get sideways for really long periods of a time -- and that's ridiculously fun, so long as you’re not hitting anything.
I should also mention it's a common misconception that AWD is safer for winter driving, but let me set the record straight: neither AWD nor 4WD are any better at stopping or turning in snow and ice than RWD or FWD. They’ll only help you accelerate and can give you a false sense of security.
Four-wheel drive (4WD)
A proper four-wheel drive system is what you'll get in a Land Rover, Land Cruiser, or Jeep. You can manually put it in a two-wheel drive mode (2H) that operates just like RWD. Or you can put it in what’s called 4H, which in addition to being a popular high school club in rural areas, is meant for street driving, and means all the wheels are operating a little differently from each other -- much like AWD.
But what differentiates it from AWD is a separate mode known as 4L, or four low. In this mode, all four wheels are locked together and will spin at the same rate at all times. You don't really want to use this on the street, but if you’re stuck in very deep snow or mud, this is the best way to get out, because there’s no adjusting, just the pure pulling power of all four tires working in unison.
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