All wheel / 4 Wheel Drive Vs Front wheel drive

I had many European (front wheel drive) cars, and believed they were great... until I purchased a 4WD Subaru: difference is amazing: smooth turns no matter how fast you drive. Car is stable in mud, snow or ice; uphill or downhill...

Despite my Impreza is not intended for off-road driving, I also drove it on loose sand and pebble roads with no problems at all.

In regard to your question: yes, they are much safer than any other type of cars under any road condition.

First let clarify 4WD vs AWD.

A vehicle that is 'All Wheel Drive' (AWD) will always have power distributed to all four wheels barring any mechanical issues.

4WD vehicles are normally driven in a 2 wheel rear drive configuration with the option to engage the front wheels.

doc is correct about AWD and 4WD vehicles handling better in mud, snow, ice, sand, wet pavement and other conditions with reduced or limitted traction. The main reason behind this is due to a more even distribution of two basic forces to all four wheels. First is the force generated by the engine and the second is the force generated by braking.

I have written a half dozen drafts trying to explain the dynamics of 4WD on ice but my mind seems to be in a fog today, maybe someone else could do a good job of it.

But let us distinguish between ice, as in sleet, and ice-like, as in snow or packed snow. No rubber-tire'd vehicle without chain/cable/studs on at least two (constant or variably-constant)drive-wheel tires can be safely controlled on extensive ice--period. If it's ice, the prudent course is to leave the 2-by, 4-by, or all-by in the driveway or garage. If you are in the south, and your employer has southern-supervisory mentality...better to forfeit the $hours than the sure-to-be much higher $repair and $liability bills.

Thats simply untrue. I live in snow country and belive me, 4wd is all you need to get around in snow and ice. And you don't need chains. 4wd works in a push pull effect. If your rear end wants to slde, technically it can't go very far because the front end is pulling it in the direction you are driving. If your front end wants to go, it can't because the rear is pushing it in the direction the tires are turning. It is possible to loose control if the whole vehical slides all at once, but thats where knowing how to drive comes into play. Most people freak out and slam on the brakes wich only causes a wreck. But if instead in a 4wd or AWD you use the concept of the push/pull effect and the gas pedal, you can easily control a vehical out of a slide. If it's icy out, you wont be going faster than 35mph anyway, so in 4wd or AWD in a slide, try keeping your cool, steer in the direction you want to go, and feather the gas, don't gun it, just feather it. And although front wheel drive isn't as good as 4wd or awd, it still does pretty good in snow and ice because your steer tires are pulling, thus, it's working to pull you in the direction your tires are facing. I do agree though that no matter what the conditions, using your head and staying humble is the safest bet.

The original motivation for 4 wheel drive was for off-road driving. You were advised to switch to 2 wheel drive for road traveling with speeds restricted to 45MPH.

The technology improved to such an extent that 4WD can now be used at high speeds.

In my lifetime the drive system advanced from rear to front to 4WD with remarkable progress each time. What next? Surround drive.

Hi PeterR,

As Richard L pointed out there is a difference between 4WD and AWD and generally 4WD vehicles only drive 2 wheels but have the ability to drive all four. Most 4WD vehicles drive the rear wheels by default but there are exceptions to this. The early Subaru 4WD vehicles drove the front wheels by default but could drive all 4 when needed.

The problem with 4WD is going round corners can be difficult and produce incredible strain on the drive train. The problem is cased by each of the four wheels following slightly different paths around a corner and so needing to rotate at different speeds. If they are all fixed together by the drive train then they can't rotate at different speeds. This can cause enormous torsional forces to build up in the drive train and can snap drive trains or strip gears.

With 4WD vehicles you get round this by only using 4WD on slippery or loose surfaces where the wheels can easily slip and stop the build up of these forces. How you engaged 4WD varied from vehicle to vehicle and in some cases you needed to stop and lock the hubs on the normally un-driven wheels to engage 4WD.

In the early 80s Subaru offered a system that could engage 4WD at any time by simply operating a push button switch that was located on the gear lever. This gave you the best of both worlds as you could drive normally in 2WD and as soon as you felt the wheels starting to slip you could pres the button and engage the 4WD.

At about the same time Audi developed a system that could be used to drive all the wheels all the time and did not have the wind up problems. The way they got round it was to install a third differential that connected to a front and rear differential one for each of the axles.

This three differential system has evolved and now the center differential is constructed in a way that it can vary the amount of torque going to the front and rear wheels. It is systems like this that are referred to All Wheel Drive as they drive all four wheels all the time. They work by monitoring a whole host of parameters and supplying the appropriate amount of torque to each wheel. For example when you are accelerating and the rear wheels are supporting 80% of the vehicles weight then 80% of the torque goes to the rear wheels and 20% to the front.

AWD systems like this offer phenomenal performance and handling characteristics and cars like the Subaru Impreza WRX offer traction and handling characteristics that racing drivers could only dream of only a couple of decades earlier. An AWD system coupled with traction control, anti lock braking, anti spin control can be quiet frightening when unleashed by somebody that knows what they can do. You will also find that most of the cars that compete in the World Rally Championship are AWD vehicles like this.

Lamborghini also have an AWD system like this and from what I have been told all the vehicles they produce now come as AWD.

So, in summary, 4WD is a system that normally operates by driving 2 wheels but can drive all four wheels when on slippery or loose surfaces that do not offer good traction. AWD systems drive all four wheels all the time but have some sort of mechanism to control the amount of torque that is being supplied to each of the wheels.

As for safety and which is better it all depends on how you drive the vehicle. I personally believe AWD is a good thing and treat it as an added safety margin and they certainly do handle much better than conventional 2WD systems. However, they can be abused and if you push an AWD system to the point it lets go you will be in a whole lot more trouble than when a 2WD vehicle lets go. The reason is that for an AWD vehicle to let go you will more than likely be going a lot faster and this means a bigger mess and more dangerous accident.

Dear MASU,

I don't understand how the torque can be divided between the front and rear wheels in proportion to the loads on them. Another point is regarding the third differential. Will this not defeat the whole purpouse of all wheel drives? When say; one of the rear wheels slips in mud, the third differential would not drive the front wheels for the same reason as in a two wheel drive the differential would not drive the wheel which has grip.

Modern differentials are of the "limited slip" variety, so they will not allow all power to go to the one wheel which has lost contact with the ground.

Thank you. I have undrstood the limited slip differential. But it does rather dilute the original idea in that it would reduce the differential action. In the extreem I would imagine that it would cause tire wear when turning as the inner wheel which has less load on it would tend to spin too fast and scrub the tire.

I think you misunderstand the idea of a limited slip diff. This allows a speed difference between inside turn and outside turn wheels. I think you are thinking of a locked diff.

The limit on the amount of slip is set to equal the amount required for the turn being made, so almost guarantees that each wheel spins at the correct rate for the turn.

Hi Masu, as usual, I couldn't put it better myself. Any body want proof, follow the link.....

http://www.wrc.com/

A fact that alot of people don't know because of the name 4wd is that on most vehicals with 4 wheel drive, when 4wd is engaged, you are still only sending power to 2 wheels. One front and one in the back on the oppisit side. They are exceptions to this. But if you look into 4 wheeling as a sport, you will find that most 4 wheel guys, like myself, have "locked the differentials". They sell lockers you install in your diffs, most are vaccum actuated. But it is expensive. A locker runs anywhere from $500-over $1000. So you have guys out there like me who just weld the spider gears and get the same effect. The only issue is that now the diff is ALWAYS locked putting power to both rear wheels all the time.

AWD vehicals dont have the turning problems on dry pavment that the 4wd does becasue inside the transfer case there is a differential allowing the front and rear wheels to turn at different rates of speed.

I live in upstate NY were we have winter six months of the year. In principle I believe four or all wheel drive is better however too many people get a false sense of security. When I drive home from work during foul weather the vast majority of vehicles I see off the road stuck are four wheel and all wheel drive. You may have all wheel drive but everyone has the same four tires to stop with and when all those driven wheels are working against you when you loose control it's much harder to recover than with a two wheel drive vehicle.

So very true. You will go through deeper snow and up steaper grades with 4WD/AWD. It will not stop you quicker. Learn how to handle a AWD power slide ... i.e. zoom around in a deserted parking lot... before you start getting too confident on the roads.

Tires are the probably the biggest factor of traction. Anyone who says all seasons are as good as dedicated snows does not get a lot of snow.

I'd go as far as saying that in 6 inches of snow or less (taking away the advantage of truck's/SUV's ground clearance) a front wheel drive with excellent snow tires would handle snow better than a 4WD.

Also, snow tires have come along way, but they still are rubber. As someone previously stated... the only thing that will work with ice are studs, chains, cleats.

Also, snow tires have come along way, but they still are rubber. As someone previously stated... the only thing that will work with ice are studs, chains, cleats.

Not a completely true statement. The "BLizzak" tire came out 15 plus years ago and uses wlanut shell in the rubber compount to provide better traction and braking power on ice than any studded tire. Rubber compounds have advanced to the point that the old studded tire is becoming obsolete. The only reason that the studded tire remains is because it is cheap. I'm currently running Bridgestone Revo dualler tires on my truck and have driven over mountain passes and on roads covered with frozem rain with better control than any studded tire. Then again I'm talking about a tire that costs $165.00 USD each as compared to the $50 USD each studded tire.

As noted in another post driving a 4WD or AWD on a slippery surface is different from from a 2WD vehicle but with a little training and practic an AWD vehicle can recover from a slide quicker than a 2WD vehicle. 2WD,4WD, AWD, FWD or RWD, it really dosen't matter if you don't know how to drive in the first place.

The other problem with studded tires is, in the northern states like Wisconsin and Minnesota, studded tires have been outlawed because they tear up the roads when driven on dry roads. Other than that little problem studded SNOW tires are great.

I am curious Richard... what part of Oregon? I grew up in Klamath Falls, and had no choice in learning to drive in the crud. Now in the Portland area, it seems like everyone forgets how to drive in it, and with the first snow every year, all hell breaks lose.

Sincerely

Bill

Born and raised in Yakima and have lived in Denver as well as many other cold and snowy places over the years. My driving experience and training as an emergency responder in the military and as a civilian in addition to personal driving experience of over twenty five years qualifies me to make the statements I did. Does this answer your implied question? (what I perceived as an implied question)

No implications intended... I just noted that you were from Oregon, and was just curious if you were from "my part of the world". I did just the opposite... born and raised in Klamath Falls, but I am now in Washington (Vancouver). I think that we both agree though, that if people would only use a little common sense when driving in the crud, it would make life easier for the rest of us...

Bil

I currently reside in Portland OR just a stones throw away.

Anyone truly interested in seeing the need for and the benefit of AWD/4WD vehicles need only come visit my corner of the world. Where I live, Iqaluit, the capital of Nunavut in the the Canadian arctic, we could not survive without our 4WD vehicles.

In this place... blizzards can last 3 days or longer and quite literally the whole place shuts down. This winter, for example, we had 6, or was it 7, snow days. A "snow day" is just what like it sounds like. Everyone listens to the radio in the morning and if your employer has called a snow day, they inform the radio and they announce it on the air, then you hunker down until ends. From what I have been told... the longest a blizzard can roll for is 6-7 days.

Oh... by the way, "winter" has not ended here yet. We had an bit of snow yesterday and the temperature has not made it over freezing for more then 5 hours yet.

Normally... no one calls a snow day until the city announces it is suspending all municipal services and is pulling all of their vehicles off of the road, including snow plowing equipment. Drifts across roads here have gone 25-35 feet high in spots.

The end result of the blizzards is roads that are impassable by anything other then a vehicle equipped with AWD/4WD capability. It is quite common here to have a to do a fair amount of snow plowing with your vehicle to get into and out of driveways, parking lots and the occasional side street until the snow moving outfits cleans the place up. As to shoveling... forget it. Snow banks by the road at the entrance to our driveway have made it 5-7 feet in height and 7-9 feet deep. So when its really bad... we go nowhere.

As to "all season tires", forget them, here... winter snow tires, with "studs" if you can get them, is what fits the bill.

Obviously, the AWD scenario offers the best of both worlds and is the superior option. My employer, the territorial government, buys vehicles equipped with both AWD and 4WD. Most people movers (Explorers, Blazers and Jimmies for the most part) are all AWD and the pick-ups are all 4WD.

In town... the regular folks buy just about anything. My own vehicle is a Suzuki Vitara 4WD equipped with high profile winter lugs and the combination is great. The little bugger is a fairly stable mountain goat. The only complaint I have with the Suzuki is... its a tad underpowered.

I can attest to the fact that 4WD does present issues as far as torque delivery being rougher and more of a brute force system versus the AWD offering. While snow drift busting earlier on this winter, I snapped a drive shaft on a front wheel. A quick $1000 out the window.

Been there done that-In Colorado Driving mountain passes with 2-3 ft of snow was all too common. Other traffic and ice beneath the snow or black ice were the main problem's debate over awd or 4wd boils down to -if you are going down a mountain and are locked out of 4wd (2wd only ) you can hopefully get out of a spin on ice by easing off on the throttle and only use brakes sparingly (you could wind up down a 1,000 ft cliff before you could correct if you lock up your brakes and go over!) The awd is great under most circumstances and it would be my second choice-but I have seen many an awd down a canyon when the torque outran the tire friction-that is either the awd put the vehicle in a spin on ice or the front differential locked up and caused just a slight difference that started a spin.

I have driven front wheel drives in mild snow and have had the least amount of trouble. But when the really bad stuff came and the snow got deep big tires and chaining up is the only answer and deep snow without underling ice can actually help to stop a skid!!

The blizzard tires work AFTER the snowplow has done his job and the are good for traction starting and stopping. Wide tires will get you up on deep snow and could get you killed on an icy intersection.

My experience after 30 years in some bad stuff is that there is no panacea they all have good and bad points depending on the conditions!!

4WD is to sugar as AWD is to sweetener.

In other words, AWD is the "DIET" version of 4WD!

Not necessarily. However, AWD and 4-WD are very subjective terms. There are many variants of each and they work differently.

I would say, as a generalization, 4-WD is a more primitive version of the all wheel driving family. 4-WD used to come in two flavors. Jeep had a Select Trac and a Command Track 4-WD system, for example.

If memory serves, the select track, when engaged, will send power to one front wheel and one rear wheel. The selected wheel is generally the one with the lower friction content. That seems odd, but that is how a traditional rear wheel car works. The tire with the least traction gets the power, unless you have limited slip, which will turn the non spinning wheel by distributing torque via a clutch in the rear differential.

Command Track actually locks up the differentials so that both left and right tires get power as well as a front to rear lock up. The downside with Command Track is something called wind up. Not only when you turn do the wheels need to spin at different speeds, but slight differences in tire circumferences will produce torques that cause the tires to skid slightly. These forces can wear the mechanical parts of the car and its tires.

AWD uses more sophisticated approaches that usually require a computer. The sensors employed for ABS and other sensors that monitor G forces and throttle and brake controls divide the engine torque through a system of clutches. When a wheel slips power is diverted to the other wheels. Another approach is to selectively apply the brakes to the slipping wheel via a computer.

AWD and traction and stability control all have a lot in common. A computer controls the power applied to the wheels and the brakes or sometimes limits the engine's fuel supply to keep the vehicle going where the computer thinks the driver wants to go.

These systems are invasive and generally work pretty well, but if you are performance driving on a track they can rob time from your laps. Some of the better systems will improve lap times, but they are pretty complex and designed for performance. The Formula One cars are a good example of how you can reign in too much horsepower and make an unwieldy car drivable.

So, generally, AWD is a better system than 4-WD, but there are exceptions depending on the vehicle, the conditions, and the task at hand. For safety, the most useful tool a driver can have is the wet-ware that lies between their ears. What you drive is not as important as how you drive!

My Ford Expedition had 2WD AWD and 4WD High&Low range. Most 4WD vehicles have and auxiliary transfer case that provides "Low Range". A snow covered trail in Montana seemed like a great place to cruise in AWD. We had to shift to 4WD "Low Range" for the torque required to churn through the deep snow.

Two wheel, front wheel drive, provides better traction than rear wheel drive. The weight of the engine over the drivers and pulling rather than pushing contribute. I crossed the Canadian Rockies from Vancouver to Calgary with a foot of snow in a Ford Escort with street tires and no chains. Stupid? Yes but impressed with front wheel drive. You could spin the drivers while directing them with the steering wheel.

Finally; When crossing a deep ditch or an icy or muddy slick spot, especially up hill it may be possible to push the front end across and then pull the rear end across with 4WD.

Without a limited slip differential or other power management system more miles have been logged with ONE wheel drive (One rear wheel or the other but not both.) than any other. Most 4WD are TWO wheel drive with one in front and one in back driving.

A very high percentage of miles driven do not require the additional traction and extra energy required for auxiliary output. For highway driving a system with two wheel drive front or back is easier on tires and saves energy. An AWD system that can be turned on for wet or slippery conditions would be good.

To increase any driver ability some exposure and practise under controlled conditions help anticipate the action and necessary reaction required if the vehicle slides or spins. An unplowed shopping center parking lot or hard frozen lake are two areas where breaking, slip sliding and power wheelies can be practised.

Without a limited slip differential or other power management system more miles have been logged with ONE wheel drive (One rear wheel or the other but not both.) than any other. Most 4WD are TWO wheel drive with one in front and one in back driving.

Side note driving tip #1. If one of your wheels is just spinning due to lost of traction try gently applying you brakes. This may be able to direct enough power to the wheel with traction to get you moving.

Just from my own experience with a '91 Jeep Cherokee and a '99 Grand Cherokee. There are different settings of 4wd, Full time(high & low) which has a differential slip on the front wheels to prevent tire and drive train damage on roads. And a part time 4wd setting that is supposed to only be used on sand, mud and snow, off road. My understanding is the part time 4wd locks the front drive axle so there is no differential slip between the front wheels, handy in loose ground conditions but destructive on asphalt or other rigid surfaces.

Little naive me: I thought that the furthest away the point of traction is from the center of mass, the greater the mobility and stability.

Was I totally wrong?

Isn't this what AWD and Quatro all about?

This reply is from someone that has been driveing front wheel drives since about 1963. If I never have another rear drive car that will be ok. The only thing that 4 or all wheel drive vehicles do is make you more brave, and get you in farther before you get stuck. Front wheel drive is a good system in a car, if driven within the capabilities of the car. (I only got stuck twice this last winter thru my own stupidity) once I was able to get out on my own and the other time I needed help. As long as you can keep the front wheels firmly planted on the ground,you can keep going. If snow builds up under the front of the car,and lifts the front weight off of the wheels you are all done. The biggest problem with all/4 wheel drives is, you have to drag a whole extra drive train arround all year so you will have it the 15 minutes when you need it. Other than that you are looking at a lot of extra weight and wear on the whole system. Not to mention you have to pay extra to get 4/awd in the first place,then your insurance will be more expensive because of the added expense of repairs from an accident. If you temper your driving to conditions,and don't try stupid stuff,front wheel drive should do you just fine. Learning to drive in snow goes a long way towards not needing 4/awd.

"The only thing that 4 or all wheel drive vehicles do is make you more brave, and get you in farther before you get stuck."

Hi Hilltopper,

I must say I do not agree with your posting: you can get into deep S#*t driving any car (even a Hummer)!

A good driver also knows the limitations of the vehicle he is driving; and will avoid any situation that puts himself or third parties in danger.

Te best place for driving a car to under adverse climate conditions is a parking lot.

Those who feel braver for driving any car should get an appointment for an electroshock ASAP.

If dragging extra weight (or increasing fuel consumption) is an issue, why are so many people driving 2WD cars around weighting as much as a pick up truck?

A much better choice is an AWD compact car that weights less and provides a much safer driving experience under any road condition.

You may agre or not, but AWD is here to stay!

4W drive seems better off for road handling and off road conditions , but there is one more concern regarding fuel effeciency that all wheel drive have lower milege as 2 W drive version , may be due to frictional losses while transmitting power to all wheels , all wheel drive with wider tyres is far better option for snow region driving

Simple answer - four wheel drive (four driven wheels, forget the tacky acronisms) is better provided it is provided with vaguely up-to-date technology for the differentials and the weight distribution is somewhere near even (which it isn't on any of the conversions of front-drive saloons). Harry Ferguson proved it conclusively with the Jensen FF, far and away the best road car you could buy in 1967 forgiving the thirst. It was also neatly endowed with anti-lock brakes.

As so many have commented, this all fundamentally depends on what use you're putting the vehicle to or where you live.

is chaining up all 4 wheels on a 4 wheel drive a good thing to do?

Chaining up all tires is pointless. Mostly chains are used for traction in starting out or getting you moving. They don't keep you from sliding. Nothing keeps you from sliding. You can lose control in anything you drive. It's all about keeping your head together and knowing your limits. You only need to chain your drive tires, on a 4wd, I wouldn't even bother with chains.