krovek42: 4WD and AWD roughly do the same thing but in different ways, the car is proving power to all four of its wheels. The difference is how that power is divided between them. An all-wheel-drive car can allow each wheel to turn at a different rate, while a four-wheel-drive car generally has its wheel all turning at the same rate. This 4WD set up is better for offroad driving, but can cause problems in city driving, where the inside wheels need to turn slower around a corner than the outside wheels do. Because of this, a lot of 4WD cars are designed to be able to switch to rear-wheel drive when the 4WD is not needed.
samwstew: 4WD is typically selective (can be driven in 2WD or RWD) where AWD is always on. Typically 4WD uses a mechanical center differential with no slip (chain or gear drive) where AWD uses a viscous coupler (kind of like a wet clutch) where it can have some “slip” and direct power to front or rear as needed.
Obviously very basic description but hope you get the idea.
GodMonster: All-wheel drive is in some ways similar to the full-time 4WD system in that it also sends torque to all four wheels constantly. However, most modern AWD systems don’t offer drivers the option to operate in two-wheel drive and, unlike the 4WD systems, the differential between the front and rear axles cannot be locked.
beer_demon: If you have more than 4 wheels, then AWD > 4WD! 🙂
It’s about traction distribution, AWD is a type of 4WD that is on all the time, so usually changes traction distribution according to what use you are giving it.
makkLyfe: 4 wheel drive means the car normally uses 2 wheel drive, but has the option to go 4-wheel drive (newer cars usually switch automatically, old cars you would have to manually change it). All wheel drive is all wheels, all the time, i.e. 4-wheel drive all the time.
WRONG_ANSWER_OOPS: Different manufacturers and people use the terms differently, but in general:
4WD = off-road cars. The 4WD system can be turned on/off by the driver so the car is only driving two wheels normally, but engages the other two for difficult conditions. When engaged, the front and rear axles are connected mechanically – there’s no (or little) provision for different wheel speeds as you would experience when taking a turn in the road.
AWD = normal/sport cars. All four wheels are driven at all times, with a differential in between to allow “slippage” when taking turns. This is better for road use, but not as good for difficult terrain.
dont_get_captured: These days 4WD means you can switch between 2wd and 4wd. AWD you don’t have a choice.
As far as what wheels get torque and when – that is more a matter of what differentials you have in the front and rear axles.
LSD (limited slip) will allow wheels to slip a bit in tight low speed cornering – this helps with not destroying your tires in parking lots for AWD and 4WD systems
Locking differentials are a different beast and will actually force front or real axles to spin the wheels at the same rate and time.
NewAppForReddit: And what about dual motors and torque vectoring? (Ok ok I show myself out…)
PulledOverAgain: Prettt simply put, AWD has a center differential which allows front and rear axles to rotate at different speeds. 4WD does not have this center diff so at all times 1 front and 1 rear wheel have to rotate at the same speed.
Sometimes its how a manufacturer names it too. I know for a time at least the Jeep Cherokee could run in a full time 4WD mode which had an open center diff, putting it in part time 4WD mode would just lock that center diff.
tylerthehun: I’m sure different automakers will implement it slightly differently, so it’s really going to depend on the car in question. Mine has AWD which works by defaulting to front wheel drive and automatically engaging the rear wheels as needed if things start slipping. A typical 4WD set-up would simply engage all four wheels for maximum traction, at the cost of increased wear on hard surfaces.
howtospelldeciduous: There’s no official difference, but 4WD generally refers to a system designed to work best off of paved roads and AWD generally refers to a system designed to work on paved roads. AWD, like an Audi, puts the power to the wheels with the most grip, and 4WD, like a Jeep, locks the wheels so they always spin at the same speed.
Propagandis: The difference is in the relationship between the front differential and the back differential.
All-wheel drives usually have a horizontal differential that transfers torque to the axle with most resistance, making it better for driving on roads.
In a 4Wd both axles are supplied with the same torque at all times, making it better for off-road.
Nelly0112: The mid 90’s Jeeps came with a few different options for 4wd. The 2 most common were the Select-Trac and Command Trac systems. Select-Trac gave you the option of a Part-time 4wd which ocked both front and rear axles together. It also gave you a Full-time option which acted like 4wd but through a series of clutches, allowed it to function like AWD. The Command-Trac system was a Full-Time 4wd system that utilized a Vicious Coupler and only gave you an option to lock everything together in 4 Low.
argon_infiltrator: For a car to be able to take a turn you want each tire to rotate at different speeds. Think that you are driving in a circle. The outside tire needs to cover longer distance than the inside tire. Also on the rear the tires need to be able to rotate slower than on the front. This means that all tires need to be able to rotate at different speeds at any given time.
When you have a front or rear wheel drive car you have a differential connecting the driven axle. This differential allows the tires to rotate at different speeds while still both tires receive power from the engine. The differential connects the driven wheels to the power input. In all wheel drive car you actually have 3 differentials. One for front wheels, one for rear wheels and one that connects front and rear axle (middle differential or center differential). This is because each tire needs to be able to rotate at different speeds so the front and rear axles also need to be able to rotate at different speeds. Middle differential allows this while still connecting all the tires to the power input. So front differential connects the front wheels to the middle differential, the rear differentials connected the rear tires to the middle differential and the middle differential connects front and rear differential to the engine via gearbox (to put it simply).
Differentials come in three basic flavors. One type is open which means both tires can rotate at different speeds while still being connected to the power source. Second type is fully closed diffs where both wheels rotate exactly at the same speed. Third option is where the rotation speeds are linked in some way. Basically you have partially locked differential. You could have a torsen differential which uses gears inside the differential to distribute the torque between the tires more equally or you could have limited slip differential which basically has brake discs inside the differential that connect both sides with friction. Differential can also be computer controlled in various ways by adjusting how locked or open the differential is at any given moment. 4wd uses differentials that are either permanently locked or can be manually be opened or locked.
Awd cars usually use open differentials and that is good enough for daily driving. Awd can be enhanced by making the differentials “smarter” by making them computer controlled. Awd cars also use other tricks to get similar effect as locked diff by using brakes for example. These are more complex and more expensive solutions that are mostly used in SUVs that need some basic terrain driving capability.
The problem with awd comes when you have rough terrain, slippery roads or so uneven terrain where one of the tires lifts off the ground or sits on a slippery surface. A typical differential in such situation acts in such way that the tire not touching the ground (or the one with the least amount of grip) spins really fast. There are driving techniques that can help here but mechanically the simplest thing is to lock the differentials. Locking the differentials means all tires rotate at the same speed. Awd typically can not do this while 4wd can.
4wd can be fully locked. However the difference between awd and 4wd is not so clear cut in practice. Some awd cars have smart computer controlled differentials and brakes which for the most part act almost like 4wd. A 4wd is typically a purely mechanical solution that is either on or off, open or locked.
tl;dr: 4wd means diffs can be locked. Awd usually means that is not possible. With modern technology the difference is not so clear cut however.
xekushnr: Okay, I’ll actually answer your question in a very simple way.
4-wheel drive vehicles (typically pick up trucks or SUVs) are selectable in either 2WD or 4WD modes. If you’ve been inside a 4WD truck you have probably seen a switch that will let you change between them (unless it’s older, than probably has manual hubs.)
All-wheel drive is basically 4WD always on. There is no switch, you cannot trigger 4WD to turn off, hence the distinction in terminology.
There is a little more to it than this, but that’s the big difference and reason for a different term.
endmatter: Four wheel drive, aka 4×4, is a dumb brute force mechanical system that can be turned on or off and normally has high gear or low low gear. It’s bad for most 4×4 vehicles to run with 4 wheel drive turned on at highway speeds or on surfaces where they have a lot of traction (that is why you can turn it off and on). 4×4 vehicles are good for things that need raw brute force like off road stuff and very low traction surfaces.
All wheel drive is a computer controlled system that is designed for maintaining traction at highway speeds and on roads. Normally your all wheel drive car is actually only using the rear axle and only engages the front axle (some systems can control each wheel independently) when it senses it is needed.
Ihavenowand: Four wheel drive: four of the wheels drive.
All wheel drive: all of the wheels drive.
Hope this helps.
straphanger82: If the car has 4 wheels, it’s the same thing. Subaru people like to tell you their car is “All Wheel Drive” – this is true but doesn’t mean much. All the fancy features (torque split etc etc) you get as part of a modern 4WD system make it much cooler but at the end of the day it’s 2 different terms for the same thing.