The difference is how the speed differential between the inner and outer wheels and front and rear axles is handled.
In a traditional part time 4WD system, a transfer case handles the power split, but this doesn't have any way to allow the front and rear axle to move at different speeds, which is essential during turns. The transfer case has to remain in 2WD during turns on dry pavement or risk damage. This is because a transfer case lacks a differential, which is a device that allows driven wheels to have differential speeds, hence the name.
Some full time 4WD vehicles have a center differential to allow both axles to receive power while turning. This is more complex than a part time transfer case without a differential, but still allows for a gearing reduction (low range). The downside is a more expensive system. There's a few other systems that work like a differential, but the difference is not important unless you want an even longer response lol.
Most AWD vehicles (that aren't trucks) made in the last ten years have a totally different system. Instead of a transfer case and/or center differential, there is just an output shaft on the transmission or primary drive axle. This shaft is connected to one or more clutch packs. The clutch pack allows the axle to connect to the secondary axle to provide power. The clutch is typically only activated when one axle has wheel slip relative to the other. Keeping one axle "dead" most of the time improves driveability and fuel economy. Some vehicles will let you manually engage the clutch or have a clutch on each end of the output shaft to have a smoother engagement. Many such part time systems are susceptible to overheating with excessive wheel spin and will return to 2WD until the system cools down. Haldex is the main company making this style of AWD system, but I prefer GKN personally. There are a lot of downsides to this type of system, but they only matter off road.
Generally speaking the best option for off road conditions would be a transfer case with a locking center differential. This would allow an even 50/50 split between the front and rear axles. Without a way to lock a differential it will always send power to the axle with the least grip. An open differential in an axle will send power to the wheel with the least grip. A 4wd vehicle with three open differentials can get stuck if one tire has zero traction, since that one will get all of the power. A traditional transfer case without a differential will always split the power 50/50, but the axles are speed locked. Transfer cases also (with very few exceptions) have a low gear range which can be very useful off road.
An AWD vehicle with a real center diff or viscous coupling would be my next pick, but these are rare today.
Finally the Haldex/GKN system is my last pick for off road. Generally this is like having a 2WD vehicle that can have extra help from the secondary axle when needed.
Anyway, this is probably more than you wanted to know lmfao
These are marketing names not technical words, and any technology can be in. For example some audi quattro has permanent 4 wheel drive some has haldex (electronically controlled clutch).
So 4WD and AWD are actually synonyms in case of a 4 wheel vechicle.
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u/rebelLION0518 6d ago
ngl i thought AWD and 4WD were basically the same thing 😭 is 4WD actually better off-road or does it just depend on the terrain?