AWD, 4WD and 2WD systems explained Just in Time for Winter

Here’s a secret about me I’m kind of a girl gear head. Not like extreme or anything for example I don’t think I know what a torque wrench looks like but I know things. Well some things at least. Let me set the scene here for a second; one of my biggest childhood friend fights was about whether our dad’s trucks had 4 cylinder or 6 cylinder engines, I had a subscription to car and driver since before I could drive and I spent the majority of my off time in college on car forums. Specifically the Xrerra owners club and car and driver. A few years ago I was helping my mom pick out a new truck and for the first time in over a decade we were straying away from Nissans. Which meant unfamiliar territory. We were trying (well I was at least) to keep track of all the drive systems and compare them fairly and it was hard. Especially the AWD offerings. At the time she had a serious commute, sometimes in the winter, and we were potentially leaving a REAL 4WD system behind for the first time.

So I said I know things and I do and did about this stuff. I knew about differentials and what one vs 2 in a car can do. About the speed and selection restrictions of 4HI and 4LOW and manual vs push button selection. I knew how a symmetric and asymmetric all wheel drive systems work and direct power in the event of wheel slip detection and the particular pitfalls of RWD in the snow. I also knew/know there is a lot of myths out there about 4WD’s being the best but I was struck by two things. Just how hard it was to keep track of all the AWD particulars among brands and more importantly the dubious names for them bordering on misleading in some cases. I came away thinking “this should legitimately be regulated to protect people!” So as winter driving season is upon us once again now seems like a good time to go through this for everyone. We will go through what each one means and does in the level of detail you need to know to be informed and clear up some myths along the way. Finally we’ll spill some tea on the shady practices of how certain brands name their drive systems and why what they call them shouldn’t matter at all to you. Ps I’ve owned all but one of these drive systems in the winter and driven the last one longer term one winter too. Once you read this you might not know everything but you’ll know everything you need to!

2WD (Front and rear wheel)

Front wheel drive: Most cars (especially sedans) are front wheel drive (fwd) and are the default for 2WD cars. Common models include, Honda civics, accords, Toyota carollas, and camrys, accents and the like. There are LOTS of front wheel drive cars out there and they are very, very drivable in the snow. These cars sort of have a differential but it’s part of the transmission and called the transaxle but you don’t really need to know that. In these cars 100% of the power is directed to the front wheels 100% of the time. That’s totally cool though because most of the weight of the car (engine and transmission) is directly over the drive wheels. That means that they handle very well on slippery roads. With very good snow tiers on heavier models of cars with fwd you should have no problems in most conditions. Even on lighter cars having all that weight over the drive wheels makes them pretty stable. I and other more expert people generally consider a fwd car with good winter tiers to be a very safe winter set up. I drove a neon, Sentra and Carolla for a total of 7 winters with this set up no problem all with winter tiers. The nice thing with fwd is in the event of a skid you should do what your instincts say and steer where you want to go should you start to slide.

Carl had enough room in the trunk for my bike, was a great place to do headstands and stayed on the road in the snow!

Rear wheel drive: A truly and only rear wheel drive car is actually a pretty rare bird. You can expect to find this set up in sporty cars and pick up trucks not equipped with 4wd. More on that in the 4wd section by the way. Rear wheel drive is what it sounds like 100% of the power goes to the rear wheels 100% of the time. This is said to make steering more responsive but I don’t really know about that. RWD cars get a bad wrap in the snow and probably deserve it for a couple of reasons. One is that the drive wheels have almost no weight over them which leads them to sliding easily in the snow. The other thing is that when they do slide you need to steer into the skid which let me tell you is the LAST thing that feels natural to do. If you are in the process of sliding off the road or say into a fence overlooking a pool… it does NOT feel right to steer more towards that hazard!!!! Can you drive these safely in the snow, yes technically but it’s probably not ideal. Many pickup trucks are RWD and their owners carry something heavy like concrete patio stones around all winter in the box to minimize this effect. Yes that does cost a lot more in gas and wear and tear if you’re wondering. Even with knobby tiers these vehicles can loose traction easily outside of winter conditions on say flat wet lawns and leave you spinning your wheels. If you are going to attempt this set up great winter tiers are a must and I would recommend a few slippery driving lessons from an expert. I drove a RWD pickup for 1 winter in the snow last year (only when it surprised me) and now I have a 4WD one so you know how that went!

Taylor was a good truck for yoga and summer but with only RWD winter was not her time to shine!

(REAL) 4WD

These are actually a very rare bird in SUVs now. You might even think you have this even though you don’t. There are lots of misleading names out there but read on for that. A 4wd has one thing that a awd will never have and that is the ability to lock the front and rear drive trains together using a locking center differential or more often a transfer case. Once locked (by either pushing a button or pulling a lever) the front and rear axels and tiers must turn at the same rate at the same time through the front and rear differential. This means that any wheel that has traction will propel the car giving you movement in the worst of conditions. Because of this a vehicle with 4WD engaged can do things and go places that no AWD ever will! Correctly this is technically a part time 4WD system but I believe this is the ONLY set up that should be allowed to call itself 4WD! The components that make up a 4WD system are heavy and expensive and therefore rare in truck and the odd car models. Many, many SUV models that claim to be some sort of 4WD lack a transfer case or locking center differential which means that the front and rear tiers are still allowed to spin independently and therefore DO NOT actually have 4WD no matter the badging they carry.

4WD is pretty great but it’s not without it’s drawbacks. When not engaged these vehicles are actually RWD meaning that unless you do push a button in advance these cars have the set up that’s most likely to get you into trouble. Unexpected ice really can drive you off the road. Engaging 4WD in conditions where its generally not needed like dry pavement causes binding in the transfer case as wheel slip is limited during turns in regular driving conditions. This causes damage to the very expensive drivetrain and can lead to major repair bills over time. The drier the road and the faster the speed the more damage is caused to the system. Often there are top speeds at which the vehicle can be driven without causing damage and though shift on the fly is possible many experts argue that it’s best to engage the system while stopped limiting the driving conditions it can even be used in.

Many owners of these sorts of vehicles believe that since they have 4WD they don’t require snow tiers like my dad and instead use either all seasons or mud and snow tiers (just knobbier) which are made of a harder rubber compound. That’s what we did for a long time until my new to me Xterra came with brand new winters. The difference was night and day and my entire family was converted! It is true that with 4WD engaged you may be able to power through conditions with all seasons on but this set up is far from ideal. Putting winter tiers on these rigs to really is the best bet because should you find your self in a low friction situation without 4WD engaged (it happens) specific winter tiers help you maintain control in your currently rear wheel driven vehicle. I’ve driven a few 4WD SUV’s and have a 4WD pick up for this winter. They include a Nissan Pathfinder, Xterra, Jeep TJ and GMC Sierra for a total of 11 winters. While they are unquestionably the most capable in winter conditions with 4WD engaged the ongoing decision of whether or not to engage 4WD or not does sometimes add to winter driving complexity.

Clyde the Jeep was pretty great in the snow!

All Wheel Drive

Buckle up folks because there are almost as many AWD set ups with variations in technology as automakers that use them. We will get into specifics here but I’ll err on the side of understanding rather than specifics and provide you with external links if you want to learn more. There are so many AWD systems out there running the gamut from pretty much useless to functionally more useful that 4WD and we will get into that. Automakers use all sorts of names for these systems, some are incredibly descriptive while others are pretty much out right lies. Manufacturers also don’t have to disclose exactly how power is distributed between the axels and wheels citing trade secrets so sometimes it’s almost impossible to know exactly what you’re buying but there is a work around to that (read on for roller tests). The good news is some are very clear about exactly what you’re buying and how it works so not all hope is lost. Let’s get into it then shall we.

The hallmark of an all wheel drive system is the inclusion of a second differential which allows the car to send engine power to the front wheels, rear wheels or both at least some times. This is the case for every AWD vehicle as is the fact that under no conditions can the speed of the front wheels be locked to the rear wheels because they lack a locking mechanism entirely (see above). These cars detect wheel slip on an ongoing basis and when detected shift how much power goes to the front and rear wheels compared to normal driving conditions. That’s pretty much where the similarities stop though and what you get to know is up to the specific manufacturer. There are no laws or even conventions about what these different set ups are allowed to be called.

In the simplest and least useful forms AWD drive systems some AWD systems send 100% of the power to one set of wheels, usually the front wheels and when the computer detects wheel slip that power is then 100% directed to the other set of wheels meaning that the power is never shared between the two axels at the same time. Since all wheels can be powered sometimes this qualifies as AWD but it does very little to make the car safer overall.

A slightly more useful set up is to have the car generally powered by one set of wheels under normal driving conditions and then when wheel slip is detected a specific percentage of engine power is sent to the other wheels. This is more likely to be the default drive system for most manufactures now. Exactly how that power is distributed might be spelled out for you or it might be an impossible to find out as was the case for me with Jeeps new active drive system. After an hour of searching I gave up. AWD may get assistance from differential breaking, ABS and throttle control in helping the car to find traction. Some models do a much better job than others in this regard. 

The best way to figure out how your car performs compared to others is to search your make and model on youtube with the words roller test. (Link to an example. For example “Jeep renegade active drive roller test”. Since how these systems work can be such a guarded secret the creators on YouTube have found a way to compare how these systems work directly and that is putting two or three wheels on rollers. Add the word hill to that to take the test up a notch. Keep in mind these videos don’t even need to be in English for you to see what’s up! Sometimes a car will fail the test until the electronic stability control (breaking and throttle control) is turned off. If the car can’t get off three rollers on it’s own in any set up we can essentially call that an asymmetrical all wheel drive system and that’s what we’ve been talking about here. Keep in mind these cars will take longer than their symmetric counter parts to get off the rollers as wheel slip has to first be detected, then corrected before the vehicle gets traction and that can be several seconds rather than miliseconds as you might think. These cars will handle better than a FWD car in the snow especially from a start. At speed however the AWD system may be too slow to compensate to make much of a difference depending on how it’s set up. One winter I drove a rented Nissan Murano with summer tiers for over a month when I crashed mine. It was the worst car I ever drove in the snow! You could lock the AWD on which made it tolerable but it would kick itself out at 30 km/hr. This was 100% about the tiers and not the drive system just so we all know.

Pretty typical winter driving in my neck of the woods!

Symmetrical AWD (or pretty much)

On to the best of the AWD systems then, symmetrical AWD. So a bit of history is in order here and we have to clear up a few myths too. Symmetrical AWD is actually a trade name for an AWD system coined by Subaru. It does NOT mean that the power is split 50/50 evenly between the wheels or that it’s on all the time. In Subarus (and probably some other makes) the power is active on both axels all the time though. This means that the amount of time the car takes to find traction is greatly reduced if not eliminated. If you are looking for the gold standard to compare your ride to in those roller tests a Subaru is the best choice because with a Subaru you know exactly what you are comparing it to. The symmetrical part of the name comes from the fact that the components of the drivetrain are laid out symmetrically which doesn’t really matter to you for the sake of understanding what to buy. This set up lets Subarus get moving even when only one wheel had traction a feat no one else could do at the time and very quickly. Now more systems can manage this however the hardest test is when it is only a rear wheel with traction. So if a car with AWD is powered at both axels all of the time not just when wheel slip is detected and it can pass the rear wheel only roller test I think we can say that it is pretty much it is symmetrical equivalent at this point or at the very least much better than average. Do you actually need this level of functionality to drive in the snow? Probably not after all FWD works pretty great too but… if you’re paying for it you might as well know what you’re getting right? Since the system is always on in these sorts of cars one could argue that they are the safest option. Don’t let yourself be sold a bill of goods! I’ve driven a symmetric all wheel drive Subaru with winter tiers for three years now and it’s pretty great!

Leslie the Subaru did a pretty great job dragging my gear around for a while but you just can’t beat a full box!

A few notes about traction

You’ll hear things like I don’t care about your tiers or your 4WD nothing helps you stop or on ice. Well that is just not true it’s just not the drive system that is helping you stop. The softer rubber compound on winter tiers absolutely makes a huge difference in stopping distance cutting it down by up to half especially on ice. ABS is pretty much a given no matter how gently used your car is now and that greatly reduces stopping distance by preventing the brakes from locking up. Your ABS system can also be a crucial part of the traction control system. So service this system if the light comes on and don’t ignore it! On ice those same winter tiers do help you stop as well and ice does have some friction available. So buy some good winters. Sure it’s a pain getting them changed twice a year but each set lasts twice as long. Also remember that should you have an accident your deductible is at least $500 and that could cover a set of winters alone!

It is the case that 4WD can slip more with the system engaged at very low speeds in turns. This is sort of a moot point because this is really only a factor at speeds under 10 km/hr. You’re not likely to be on public roads driving at these speeds and you’ll have plenty of time to correct. Even if you were to hit something I highly doubt you would do any damage and I am certain you would be totally fine.

No matter what you’re driving, the conditions and how your car is or isn’t outfitted probably the biggest thing you can do is to adjust your driving style and mindset. Rather than aiming to control a skid I think you should aim to never slide at all. Go way, way slower, anticipate where water may be frozen across the road and slow down. Give miles of room between you and the next guy and break slower than you even think is necessary. Be okay pulling over and letting cars pass if you’re not comfortable and err on the side of caution. I live in Canada and I’ve done some crazy things over the years mostly in 4WDs with winters in the snow. Once My Xterra was completely covered in snow after a storm and packed in at the back from plow snow. I shoveled enough to get in it, put it in 4low and rocked it back and forth until the truck burst out the back. Another time I backed that truck up in snow so deep that it was piling up over the back of the truck as I went. Then I essentially used the grill to plow the 500 foot driveway and get out onto the road. I even drove a friend’s Suburban in RWD on a frozen lake once and she did A LOT of sliding around. It was quite fun! Notice though NONE of those more extreme maneuvers ever took place on public roads!

This winter I suspect I’ll mostly be driving Chris in the snow with 4WD, fresh winter rubber and a 500 lb concrete block in the back I suspect he’ll be more than capable! Though as of this minute I’m still more comfortable in the Sube which also has some new winter grip!

You know what else I’ve done, I’ve abandoned a vehicle in winter conditions mid journey when conditions became unexpectedly unsafe. I 10 out of 10 don’t recommend but sometimes life just gets you in a bad spot. Last winter three days after we bought our very well used RWD truck with pretty bald tiers on it I was towing a wood splitter back to the shop. At our house it was raining and well above freezing but just a few km inland it was changing over to snow and coming down fast. I should point out that new winters were going on the very next day. After a few minor slides, then some more major ones around 20 km/hr I couldn’t make it up a slight hill on a turn at all staying in my lane. I used the shoulder to find some traction and didn’t even attempt going down the hill to my friend’s house. Instead I pulled over onto someone’s lawn and knocked on the door and explained myself. My friend was home and they drove us home in their Subaru but if not I would have called a cab or hunkered down until conditions improved. Sometimes conditions are just too bad to continue and giving up is better than damaging your car, someone else’s or hurting someone. If you know you and your car shouldn’t be out there, don’t be, full stop.

What ever you’re driving stay safe this winter!

This is so important I believe that all wheel drive systems should be regulated, tested and labeled according to performance in such a way you can easily compare them. Things like ‘All time all wheel drive’, ‘on demand 4WD’ or quattro mean literally nothing and do a disservice to customers plus a lot of them are misleading! What do you drive?  What is your all time best winter ride and what’s your number one winter driving tip?

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