More specifically, what are the pros/cons of each? Why do some cars use one system over the others and which is “better”?
EDIT: Thanks everyone for the explanations. It’s been very useful.
In: 10
FWD = only the front wheels are driving the car. A driveshaft comes from the engine and connects to the front wheels. This is the lightest & least complex system available, and therefore the cheapest. There is no long driveshaft or axles that run to the back of the car. If driving in the snow, this system will have significantly better traction than a RWD system because the entire engine bay is over the driven wheels, unlike a RWD system which usually has only an empty trunk as “weight”. Handling isn’t as good as a RWD system.
RWD = the front wheels steer, and the rear wheels drive the car. Superior handling at high speeds and through turns is the only advantage. This system is slightly more expensive and complex since there’s a driveshaft and multiple clutches connecting the engine at the front of the car, to the driven wheels at the back. Plus there is a usually a “hump” in between the seats to account for the driveshaft. This system usually has poor snow traction since there is no weight on the driven wheels. It also weighs more and has more pieces.
AWD = This implies that all four wheels, or both axles are being powered simultaneously. Full-time = this happens constantly. Part-time = one axle is powered only until “slip” is detected or the system requires the other axle to engage, in which case it engages. The part-time system saves gas by only driving one set of wheels until the full system is required (for example if the rear wheels spin in the mud). This system generally has poor fuel economy compared to a FWD system (which has the best), or a RWD system (which has 2nd best). This is because there are two axles, at least 2 drive shafts, and multiple clutches that power this system. Unlike a FWD system which has a driveshaft usually less than 3 feet, this system might have 30 feet of connections. As a result, energy is lost at each connection point. This is why a FWD Toyota Corolla will always have better fuel economy than an AWD Subaru Impreza. The advantage of this system is better handling in poor weather. So if you constantly drive in the snow or mud, this system is superior for safety. All four wheels can receive power (either full-time or part-time), meaning it’s less likely for the car to get “stuck”. An AWD uses open or limited slip differentials so that each wheel & each axle can turn at different rates. In an AWD system, the engine is connected to a transmission, and there are often multiple drive shafts to connect to each axle. There are at least 3 differentials on all AWD systems (a front, a rear & a center).
AWD & 4WD are sometimes interchangeable terms in 2023. However 4WD may sometimes refer to a 4×4 system on trucks and jeeps. This is a very rudimentary system that DOESN’T employ a center differential. This means that unlike a Subaru, both axles spin at the same rate. This type of system was created years ago, and gives 50/50 torque to each axle so that the truck or jeep can power out of the mud of the snow. The main limitation of this system is that it’s not designed to be driven on roads with traction. Since each axle turns at the same rate, the rear right wheel, the front left wheel, and the rear left wheel try to turn at the same rate. If you try to make a turn, you’ll notice that the truck or jeep starts to “lurch” or “squeal” since when a normal car makes a turn, all four wheels are moving at separate speeds. Most trucks in 2023 still have this system, and even in the owner’s manual, it’s recommended to only turn it on when you’re in deep snow or mud, and NOT drive it on regular road. In this type of system, you would drive the truck or jeep into deep mud or snow, and then you’d flip a switch and “engage” the 4×4 system. The system would be “locked” with 50% of the torque going to the front axle and 50% going to the rear axle. Each axle would spin at the same rate to power the car out of the mud or snow. Once you get back onto smoother roads, you would disengage the system and it would go back to a two-wheel drive system.
I’ve driven FWD cars, I’ve had 2 pickup trucks with a 4×4 locking system, and I’ve owned 4 Subarus which have an AWD system. The Subaru’s are the safest and require zero input in order for their system to work. The trucks require constantly turning the 4×4 system on and off.
In 2023, the biggest success of traction depends on the type of tires you are using. Even a sophisticated AWD system won’t help you much if you are using (for example) worn summer tires in deep snow. If the are you live in routinely gets snow or gets below 5 degrees celsius, you should use winter tires for months with snow and low temperature.
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