AWD vs 4WD - What's The Difference?

hello everyone and welcome in this video we are talking about the differences between four-wheel drive and all-wheel drive and beside me is the bmw m5 which actually has four-wheel drive which is very rare for a car usually cars will have all-wheel drive but usually you don't see four-wheel drive unless it's in perhaps a truck or an suv now bmw's uk website actually says that four-wheel drive and all-wheel drive and 4x4 all mean the exact same thing so perhaps this is all just marketing terms but i think there are you know what are considered traditional differences between a four-wheel drive system and an all-wheel drive system and so that's what we're going to get into in this video so here we have two simple drawings illustrating the difference between all-wheel drive and four-wheel drive and so there are a lot of similarities and don't pay attention so much to the scale of these rather to you know the things that are actually different between them and how the layout actually functions so both of them you start with your engine of course and that could be you know laid transverse it doesn't have to be longitudinal from the engine you either pass what we have in green it's either the torque converter or clutch depending on if it's a manual or automatic then goes to the transmission in purple so so far they're completely the same and then this is where they start to differ so in an all-wheel drive vehicle from the transmission it goes to a center differential in a four-wheel drive vehicle it goes to a selectable transfer case so it's going inside of this transfer case and then it's going to pass from the transfer case directly to the rear differential and if you put it in four-wheel drive it will also send power to the front differential in all-wheel drive your center differential is going to be sending that power to one of the axles pretty much all the time and then you'll have another clutch pack which can choose to send additional torque or rather to redirect that torque to the other axle so it could be the front or the rear which one you're choosing to send more to but traditionally you're going to have it be front wheel drive and then send torque to the rear differential as needed but there are many many different setups as far as all-wheel drive is concerned for more information i'll include certainly links in the video description as far as you know the different types that exist out there but the big difference between these two is that all-wheel drive the driver isn't choosing what's happening the system itself is always determining where it wants to send that torque with four-wheel drive using this transfer case the driver actually chooses do i want to send power just to the rear wheels or do i want to also send power to the rear wheels and the front wheels so what are the advantages of each well starting with all-wheel drive one of the big advantages of course is that the driver doesn't have to do any thinking the vehicle itself is choosing where does power need to go based on the traction that it's seeing but the big advantage of all-wheel drive is that it works great both off-road as well as on-road and so the reason why it works great on-road is because it allows for slip within the system so you don't have any binding like you may have with a four-wheel drive system now this means you get the performance benefits of the all-wheel drive system while you're driving on the road specifically traction so you can have improved acceleration now four-wheel drive on the other hand generally shouldn't be used on the road and the reason for this is because this transfer case often acts just like a locked differential and so what that means is if you have a speed differential between your rear axle and your front axle for example when you're going around a corner you have binding within this transfer case because it's not able to send different speeds to each differential they both get the exact same speed and as a result these tires have to rotate at similar speeds going around that corner and so because of that you have binding within it and you don't want to have that happen you'd rather just have these tires rotate now off-road you don't have to worry as much about binding because you're just going to have the tire slip on the loose surface so whether you're on dirt or rocks or things like that the tire is going to end up slipping not the drive train so it's not as hard on the vehicle the other advantages of the off-road system is that it's actually selectable between two-wheel drive so you can choose as a driver i only want to send power to the rear wheels which for an example like with this bmw that's fun to do because you can slide around you can spin those rear tires and also it's more efficient to send power to just two tires rather than to all of them and then finally the benefit of having four-wheel drive is that many of these often come with a low gear range so some folks will to say that a four-wheel drive system a true four-wheel drive system does have a low gear range which means off-road you can select that low gear range you have much more torque and you can crawl very slowly over specific obstacles now this does not have a low gear range but it does have that selectable two-wheel drive or four-wheel drive so does all of this mean that the bmw m5 can't use four-wheel drive on the road well no actually they've done something super clever and so what they've done is they put a multi-plate clutch within this transfer case and what this does is it allows for a different torque split and varying speeds between the front and the rear axles so it can send different speed to each axle and as a result that means you can go around corners without binding this transfer case and you can fully vary the torque distribution so that's a really neat thing that bmw's done it acts a lot more like an all-wheel drive system when it's in this four-wheel drive mode but it has that traditional transfer case where you can select to just use those rear wheels now if you enjoyed this video i have all kinds of videos covering different types of all-wheel drive and four-wheel drive systems that different manufacturers use and it's also important to realize that different manufacturers use different systems internally for different products so you know there's not just one company that makes the best four wheel drive system there's all kinds of variants even within a single company so it's all about the individual system not about you know what's the label of it what's it called is it called you know 4matic or xdrive or symmetrical all-wheel drive they all mean you know that's just a marketing term that means four wheel driver all-wheel drive the actual differences can be much greater than just simply that title so if you are interested i will include those links in the video description thank you all so much for watching and if you have any questions or comments of course feel free to leave those below

Channel: Engineering Explained

Views: 1,769,092

Keywords: awd, 4wd, best awd system, best 4wd system, subaru symmetrical awd, audi quattro, bmw x-drive, ram 4wd, ram 4x4, dodge truck, ford 4x4, ford truck, awd vs 4wd, awd vs 4x4, 4x4 vs 4wd, jeep 4x4, jeep, jeep 4wd, best jeep, best suv, best 4wd suv, best 4wd tuck, how it works, engineering explained

Id: Jk246sutET0

Length: 5min 51sec (351 seconds)

Published: Sun Nov 04 2018