Why is All Wheel Drive better on snowy and slushy roads?

[Chuckanut]

The local mountain pass now requires traction devices on ordinary cars due to light snow and slush on the roadway. However if one has an AWD vehicle they are not required.

Can anybody explain technically why AWD is so much better that chains are not needed under the above conditions? My personal experience has been that slippery roads are slippery roads. But, I have never had an AWD vehicle until this year.

 

[brewer12345]

You are a lot less likely to get stuck in the snow with AWD/4WD. What the authorities care about on mountain roads is making sure that you keep moving so that the road does not shut down.

 

[copyright1997reloaded]

Two drive wheels vs one. Doesn't mean much (if anything) in terms of stopping.

My philosophy is AWD/4WD plus snow tires on all four wheels (which does make a difference in stopping). Also weight in the back of my truck (4WD) and a set of chains just in case (which I've never had to use).

 

[copyright1997reloaded]

You are a lot less likely to get stuck in the snow with AWD/4WD. What the authorities care about on mountain roads is making sure that you keep moving so that the road does not shut down.

What Brewer said. Once you get stuck others get stuck behind you. I've been on roads such as going to Snowbird/Alta, and all it takes is one clown with no AWD and/or crappy summer tires and everyone gets stuck behind them, including the plows trying to keep the roads clear.

 

[samclem]

You are a lot less likely to get stuck in the snow with AWD/4WD. What the authorities care about on mountain roads is making sure that you keep moving so that the road does not shut down.

+1. If even one vehicle can't maintain traction going uphill, they block the road and other vehicles behind may also have trouble getting moving again from a standstill once stopped on the ice/slush.

 

[MRG]

In AWD or FWD one wheel from the front and back axle can drive if needed. On DWs Wrangler I can be spinning a wheel on the rear axle shift into FWD and take off; because of the traction supplied by the front axle.

 

[like2]

This guy explains how AWD works and the advantage you gain traction wise in slippery conditions

https://youtu.be/UL9LmT3fzbQ

 

[Just_Steve]

Just a little AWD video.

 

[Jerry1]

And it works well. We had a very slippery snow and the ramp to get on the freeway had a pretty steep incline (not like a mountain of course) and my AWD Equinox handled it like a champ whereas many cars were not able to make it. Kept moving in a steady controlled manner and all was good.

 

[pb4uski]

Climbing hills... 4 drive wheels are better than 2
Level ground.... same thing
Doing downhill... a small advantage if you are downshifting and using your engine to control your speed... no advantage in stopping
Curves... better control with traction to 4 wheels

Collectively enough to be a significant difference... I've driven in the snow in rear-wheel drive, front-wheel drive and AWD/4WD with all seasons and snow tires and I'll take AWD/4WD anytime.

Though I will offer that in the early 70s my dad had a Peugeot 504 diesel with snow tires... rer wheel drive if I remember right... while that old diesel had an excrutiatingly slow 0-60 and barely enough tourque to spin the tires in snow, it was a great snow car and would go about anywhere (albeit not quickly).

 

[Bamaman]

Front wheel drives do very well in snow with most of the weight of the vehicle on the front end. And the front tires climb on top of the snow instead of plowing through the snow.

Rear wheel drive vehicles still have most of the weight on the front end, and they cannot get the front tires on top of the show. They just don't have sufficient traction.

State officials must make one rule for all non AWD or 4x4 vehicles. And they choose to prohibit vehicles without 4 drive wheels from entering some areas.

 

[DrRoy]

You have more points/area of energized contact with the ground. It is not as good as chains but better than 2WD.

 

[Music Lover]

+1. If even one vehicle can't maintain traction going uphill, they block the road and other vehicles behind may also have trouble getting moving again from a standstill once stopped on the ice/slush.

Even on level ground. If the first car in line at a a stop light is FWD or RWD and has non-winter tires it takes them longer to get started and clear the intersection which leads to traffic backing up. A green light that is designed to clear 20 vehicles per hour may now only be able to clear 12 per change.

 

[ERD50]

The local mountain pass now requires traction devices on ordinary cars due to light snow and slush on the roadway. However if one has an AWD vehicle they are not required.

Can anybody explain technically why AWD is so much better that chains are not needed under the above conditions? My personal experience has been that slippery roads are slippery roads. But, I have never had an AWD vehicle until this year.

IMO, this needs to be re-phrased, and broken down for clarity.

A) AWD/4WD is better for getting moving in snow than 2WD. That is hopefully obvious, you've got 4 tires pushing forward rather than two.

But in all cases you still have 4 wheel brakes, no difference in stopping power, and this gets a lot of people in trouble. They don't realize the road is as slippery as it is, and it may be harder to stop than they think.

B) But is AWD/4WD better than chains on a 2WD? I don't know, probably depends on a lot of things, but I'd guess chains are better.

I think they are making the requirement just based on 2WD being unacceptable, and AWD/4WD is at least above that minimum requirement? I would not infer from that that AWD/4WD is equal to or better than chains.

-ERD50

 

[Car-Guy]

To answer the OP's original question. You have four wheels applying power/traction to the road vs two wheels. Pretty simple.

Note there are number of differences between AWD and 4WD system too. I won't try to explain them here but to make it simple, AWD is designed to be engaged and in use full time under all driving conditions. 4WD is designed to be used occasionally and "typically" needs to be engaged by the driver when needed. I have both AWD and 4WD vehicles. For off road use I prefer my 4WD. For on road, I much prefer my AWD vehicle.

Seems a lot more AWD vehicles are coming out these days. Even some ultra high performance cars have AWD now which gives them an advantage over their two wheel drive counterparts in competitive driving.

I know I feel much more comfortable in my AWD vehicle VS any 2WD in bad weather. (e.g. rain and snow)

 

[Andre1969]

I think one major shortcoming modern 2WD cars have, regardless of whether they're RWD or FWD, is that most people don't use snow tires anymore. I don't recall my family having any problems getting through snow back in the day, and I also don't remember my first car, a 1980 Malibu, having any real problems. BUT, we used snow tires back then. Nowadays, most people just get by with all season radials, that give you some traction bad weather, but they're nowhere near as capable as snow tires were.

 

[Ronstar]

I haven’t driven an AWD vehicle. But I’ve had several 4wd trucks and jeeps. 4wd is great because there is a lot of weight over the driving wheels when it’s in 4wd. But the best thing for battling snow and ice is good tires.

 

[pb4uski]

I think one major shortcoming modern 2WD cars have, regardless of whether they're RWD or FWD, is that most people don't use snow tires anymore. I don't recall my family having any problems getting through snow back in the day, and I also don't remember my first car, a 1980 Malibu, having any real problems. BUT, we used snow tires back then. Nowadays, most people just get by with all season radials, that give you some traction bad weather, but they're nowhere near as capable as snow tires were.

I probably would not bother with snow tires if I lived in Maryland, but snow tires are still very common in northern New England.

I recall that back in the 60s and 70s you could buy very affordable retreaded tires where the tread was a mixture of rubber and sand for traction... aka "sandpaper" retreads or recaps.

 

[Mr._Graybeard]

Front wheel drives do very well in snow with most of the weight of the vehicle on the front end. And the front tires climb on top of the snow instead of plowing through the snow.

Rear wheel drive vehicles still have most of the weight on the front end, and they cannot get the front tires on top of the show. They just don't have sufficient traction.

State officials must make one rule for all non AWD or 4x4 vehicles. And they choose to prohibit vehicles without 4 drive wheels from entering some areas.

+1 ... most 4WD/AWD also have higher ground clearance than passenger-type 2WD vehicles, which can be a plus in deep snow.

 

[jollystomper]

But in all cases you still have 4 wheel brakes, no difference in stopping power, and this gets a lot of people in trouble. They don't realize the road is as slippery as it is, and it may be harder to stop than they think.

-ERD50

+1

I am seeing more snow/ice accidents caused by folks driving too close to others or too fast and unable to stop in time. I cringe when I see someone driving less than a car length behind another when driving on snow/ice.

 

[Chuckanut]

Thanks for all the good information. You have confirmed what I suspected, but was not sure about: AWD is better than 2WD, but not as good as having a good pair of chains and/or snow tires on the car.

I tend to avoid driving in my area when there is snow. We don't get enough snow to justify mounting snow tires in November and taking them off in March. And, even the most skilled driver is subject to problems caused by idiots who can't drive properly in the snow. I'm sure we all have stories about that. :-(

 

[Gumby]

Two drive wheels vs one. Doesn't mean much (if anything) in terms of stopping.

I see that all the time around here. People with AWD driving too fast on snowy roads because they can. The speed makes it harder to stop.

 

[MRG]

I see that all the time around here. People with AWD driving too fast on snowy roads because they can. The speed makes it harder to stop.

+1000

It's people who have too much confidence and no experience with stopping/maneuvering in unfavorable conditions. I've been rear-ended three separate occasions and each time it was someone too close to me that I Watched Hit Me! Every time I secured my stop and looked to see them rear-end me! Like it was happening in slow motion, Please Stop!

Today I try to pull out of the way and let them go. Both of our vehicles are FWD but you can't stop or maneuver any better than your tires connection with the road.

 

[Music Lover]

Thanks for all the good information. You have confirmed what I suspected, but was not sure about: AWD is better than 2WD, but not as good as having a good pair of chains and/or snow tires on the car.

But it doesn't have to be one or the other. AWD with winter tires is better than 2WD with winters.

I tend to avoid driving in my area when there is snow. We don't get enough snow to justify mounting snow tires in November and taking them off in March. And, even the most skilled driver is subject to problems caused by idiots who can't drive properly in the snow. I'm sure we all have stories about that. :-(

Winter tires may be the difference between avoiding a collision due to another idiot or not stopping in time.

 

[Mr._Graybeard]

When I was still commuting, my pet peeve was the drivers who were so poorly prepared for winter driving that they crawled down the road at 25 mph. Inevitably they got a string of 10 or 12 cars and trucks following, afraid to pass because the left lane was snow covered. The slowpoke never thought to pull off -- or may have been afraid to because their crap tires wouldn't move them through a couple inches of snow.