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

[ls99]

Have 2012 AWD caddy. The manual says tractive effort is distributed to all wheels all the time and is proportioned depending on traction needs of each wheel.
In practice I find it extremely stable in all conditions. Wet or snow, unless I manually diengage traction and stabilty control, l have never felt tire spin in snowy or icy conditions. All of which we have plenty in western PA.
Mind you if traction control is enabled and stomp on gas in dry or wet condition, the thing cuts ignition around 4K rpm and feels like it is going to stall, it does not, just feels like it when acceleration is instantly slowed. Red line is at 7+K rpm.

 

[Koolau]

Back in the day when I lived in the snowy midwest, I had a Subaru w/on-demand 4WD. I QUICKLY discovered that 4WD can get you into trouble a lot faster than your brakes can get you out of it. For folks who want to learn how to drive in snow/ice with or with out FWD or 4WD, go to a deserted (maybe on Sunday) parking lot and "play" in the snow with your car. Be careful, but have fun. YMMV

 

[JoeWras]

Back in the day when I lived in the snowy midwest, I had a Subaru w/on-demand 4WD. I QUICKLY discovered that 4WD can get you into trouble a lot faster than your brakes can get you out of it. For folks who want to learn how to drive in snow/ice with or with out FWD or 4WD, go to a deserted (maybe on Sunday) parking lot and "play" in the snow with your car. Be careful, but have fun. YMMV

Yes, overconfidence. Antilock brakes and AWD don't prevent you from having bald tires, driving over confidently, or underestimating braking distance.

I have a Subaru here in central NC. It is good to navigate the 1 day per year on average we get an event. It comes in handy in our hilly neighborhood. It's fun! But I don't want to get out on the main roads unless I have to due to the braking problem, or rather, others' inattentiveness to braking.

So we typically stick inside and let it melt, unless there is a critical need. Oh, and I go for a drive in the neighborhood just for fun.

 

[pb4uski]

Overconfidence is a risk with AWD/4WD for drivers unaccustomed to driving in snow... 4-wheel traction is great for level terrain and uphill and even turning (with gentle added throttle) but does nothing to help you brake... and that overconfidence causes prople to drive faster than conditions warrant which exacerbates the braking situations.

At best you just bounce off a snowbank (been there, done that).... or worse.

 

[38Chevy454]

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.

X2, I lived in the mountains previously where you would have this happen often. Going too slow can also be bad since it can actually increase the tires slipping. Very frustrating being stuck behind one of the unprepared people. Have seen this lead to unsafe passing and several hand gestures


AWD vehicles can operate different ways. Some are fwd as std and then when slip is detected the rear tires are engaged. Some are awd all the time with essentially fixed torque split between front and rear. Some newer awd are smarter and can adjust the torque split. Traditional 4x4 are 50/50 torque split when 4wd is lock engaged. Some newer 4x4 have a position labeled "4wd auto" that basically operate predominantly rwd then if slip is detected it transfers power to the front tires. AWD vehicles are great in the snow and ice. They really do work to help you get going and increase stability. But as many have said, you still need to be aware turning and stopping in limited traction is not really helped. That is more function of the tires, and where true winter tires really excel.

 

[Chuckanut]

AWD vehicles can operate different ways. Some are fwd as std and then when slip is detected the rear tires are engaged. Some are awd all the time with essentially fixed torque split between front and rear. Some newer awd are smarter and can adjust the torque split. Traditional 4x4 are 50/50 torque split when 4wd is lock engaged. Some newer 4x4 have a position labeled "4wd auto" that basically operate predominantly rwd then if slip is detected it transfers power to the front tires. AWD vehicles are great in the snow and ice. They really do work to help you get going and increase stability. But as many have said, you still need to be aware turning and stopping in limited traction is not really helped. That is more function of the tires, and where true winter tires really excel.

Then there is my hyrbrid's AWD. There is no physical connection between the front wheels and the rear. Instead, they attached another electric motor (less HP than the one up front) to the rear axle. That provides the energy to the rear wheels when the sensors detect slipping.

 

[nativenewenglander]

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.

The Team O'Neill professional driving school is local to me where they teach rally driving as well as defensive and offensive driving to government organizations. They have quite a You Tube site, here is a video that explains the difference between AWD and 4WD.

I sent my wife to their winter driving school last year, she loved it.

 

[stephenson]

Yeah - four better than two.

The first geo didn’t include an Audi ... would have been nice to see if it, given it’s history of AWD, was comparable to the Subaru.

An interesting test, but certainly not related to raw, world conditions. One is almost always moving prior to hitting any slope... even if already going up slope ... and, 30.5 degrees? Seriously? And, smooth aluminum plate? With water?

 

[JoeWras]

An interesting test, but certainly not related to raw, world conditions. One is almost always moving prior to hitting any slope... even if already going up slope ... and, 30.5 degrees? Seriously? And, smooth aluminum plate? With water?

False.

Let me show you a few driveways around here, especially my own. Only a 4wd/awd can get up it in snow.

Also, I could show you a few crazy old roads around here with hills up to a stop light. When traffic stops, you are on significant slope at stop. This is not good modern road design, but it was common years ago.

 

[stephenson]

Sorry - I wasn't clear.

The conditions from the OP's post were related to highway driving - that is what I was responding to.

But, to the test - aluminum plate with water does not suitably represent snow, or even ice (glaze/black ice is much worse) - sure, if the entry to your driveway went up 30.5 degrees, was made of smooth plate aluminum and it was raining only on the top edge and flowing down ...

And, btw - have had RWD cars in Maine, Alaska, Canada, and Colorado. Have had FWD cars in Maine and Colorado. Have had AWD in Maine and Colorado. Clearly, AWD, and even 4WD is better than either FWD or RWD. I would probably take AWD with suitable tires (not summer highway tires, but something more common now, like All Terrain, or M/S) over FWD or RWD with chains. Perhaps if just ice, perhaps, the FWD with chains.

"Four wheel drive doesn't mean four wheel stop."

 

[JoeWras]

Sorry - I wasn't clear.

The conditions from the OP's post were related to highway driving - that is what I was responding to.

But, to the test - aluminum plate with water does not suitably represent snow, or even ice (glaze/black ice is much worse) - sure, if the entry to your driveway went up 30.5 degrees, was made of smooth plate aluminum and it was raining only on the top edge and flowing down ...

We're cool, no worries.

I agree with you on the test. Even though I have a Subaru, I'm not enough of a fanboy to ignore marketing when I see it. That video was a nice marketing tool and nothing more.

 

[ls99]

Just to add mud to the waters, there is a system called rigid drive.
Found on airport snow plows. The ability to lock the differentials of front and rear axles and the front and rear drive shafts via the transfer case. Thus make it more capable of pushing deep snow.

 

[troutnut1]

I live in Montana 20 miles from the continental divid and our ski area. Everything I own is 4WD or AWD. My Lincoln Navigator has a selector switch for 2WD, AWD, 4WDHigh, 4WDLow so I have a lot of choices and can play with them all. Normally in the winter I just leave it on AWD. My favorite snow car of all time is still a Subaru Outback with AWD. No choices or switches to forget. It’s just AWD all ofthe time. Still with all these options and 3 4WD/AWD vehicles to choose from, I wouldn’t drive any of them on our winter roads without dedicated studless snow tires like Michelin X-ice, or Bridgestome Blizzaks. All season tires aren’t good enough for me. And chains? Yes, I have a set. But in Montana when you put on chains, it’s time to turn around, and go directly home. You don’t use them just to get into deeper trouble than you are already in...

 

[Gumby]

I live in Montana 20 miles from the continental divid and our ski area. Everything I own is 4WD or AWD. My Lincoln Navigator has a selector switch for 2WD, AWD, 4WDHigh, 4WDLow so I have a lot of choices and can play with them all. Normally in the winter I just leave it on AWD. My favorite snow car of all time is still a Subaru Outback with AWD. No choices or switches to forget. It’s just AWD all ofthe time. Still with all these options and 3 4WD/AWD vehicles to choose from, I wouldn’t drive any of them on our winter roads without dedicated studless snow tires like Michelin X-ice, or Bridgestome Blizzaks. All season tires aren’t good enough for me. And chains? Yes, I have a set. But in Montana when you put on chains, it’s time to turn around, and go directly home. You don’t use them just to get into deeper trouble than you are already in...

I hear you. The young wife and I drove over the Beartooth Pass into Red Lodge in September. There was plenty of snow on the ground up there already. I'm sure it only gets worse.

 

[segfault]

I've had three AWD vehicles, and despite the alleged technical superiority of Subaru's system, can't say anything bad about Nissan's, GM's, or Audi's in terms of real world performance in snow. They all prevented me from getting stuck in slippery conditions, which is something that has happened to me with FWD and RWD cars.

My work truck is 4WD and has tires with the three-peak mountain snowflake on them. They are probably noisier than regular truck tires, but have worn really well in terms of tread life. I leave it in 2WD and have never had to engage 4WD in the snow. I figure if I start sliding around or get stuck, that's a sign to engage 4WD and get home ASAP. I do turn on the 4WD once a year to make sure I can hear the hubs engage, ergo, it's theoretically still working.

 

[ls99]

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.

They are the same people who drive too fast on dry and wet roads, ditto for turns, brake really hard and tailgate, pass on double yellow. What they they rely on is the technology built in for stability ABS for braking etc. to save their bacon when traction would be lost. And when traction is lost there is no skill to deal with being out of control. Besides Awww$hit!

 

[Hermit]

Just to add mud to the waters, there is a system called rigid drive.
Found on airport snow plows. The ability to lock the differentials of front and rear axles and the front and rear drive shafts via the transfer case. Thus make it more capable of pushing deep snow.

I have front and rear lockers on my Jeep Rubicon. I would never go faster than about 5 mph with the front lockers engauged even in dry conditions. The Jeep tends to plow straight ahead when you try to turn with the front lockers engauged. It is not fun. I think front limited slip axles would be better.



In my son-in-law's 92 Jeep YJ, he and I have both found engauging 4WD helps keep the rear end behind the front end on snow packed and icy roads. It is kind of exciting when the rear end is leading, but probably not as safe. Ask me how we both know.

 

[Mr._Graybeard]

Just to add mud to the waters, there is a system called rigid drive.
Found on airport snow plows. The ability to lock the differentials of front and rear axles and the front and rear drive shafts via the transfer case. Thus make it more capable of pushing deep snow.

My old Audi 4000 quattro had locking center and rear differentials. It had a rotary switch on the console that enabled the driver to lock the center diff only or the center and rear diffs together. It lacked ABS, but the locked center diff distributed braking stress to all four wheels so the front wheels were less likely to slip. It worked very well.

 

[ERhoosier]

The AWD rule mentioned by OP is bureaucratic.

Objective testing consistently shows AWD vehicles without snow (winter) tires have far WORSE traction on snowy uphill road than a similar FWD vehicle with proper winter tires. Of course, AWD with winter tires is the best setup but FWD with winter tires is not that far behind. IOW- Winter tires mean FAR more than AWD vs FWD on snowy roads. Well worth the investment for Northern drivers.
This British test video shows the HUGE benefit of winter tires on a snowy climb using same model SUV (Ford Kuga/Escape) in various combos of AWD vs FWD and winter vs summer tires. Short version:
AWD/winter tires>FWD/winter tires>>>>>>>>>AWD/summer tires>FWD/summer tires

https://jalopnik.com/lets-settle-the-winter-tires-vs-all-wheel-drive-debat-1462180324

 

[RunningBum]

Do a lot of people have a set of winter tires? I've thought about getting a set, mounted on wheels, so I could swap them myself. We don't have too much winter here, but we can, and when we do driving in the mountains it can be difficult. In the past 10 years I recall a 30" snow and at least two 20" snow storms, plus plenty of lower totals, sometimes mixed with ice. But the majority of the time it's clear and I could easily be driving in 50 degree weather between snows, and I read that snow tires don't last long on warmer roads. The plows do tend to clear the roads pretty quickly after storms but that can leave a layer of packed snow/ice occasionally.

I checked Tirerack and it would cost me about $1100 to get Micheline x-ice tires mounted. Those seem to be the best combination for me, rarely driving in deep snow and often driving on clear roads. Trying to decide whether it's worth it. I guess I would pay at least that much for AWD if that were a choice on my car--it's on all Foresters.

 

[Mr._Graybeard]

Objective testing consistently shows AWD vehicles without snow (winter) tires have far WORSE traction on snowy uphill road than a similar FWD vehicle with proper winter tires. Of course, AWD with winter tires is the best setup but FWD with winter tires is not that far behind. IOW- Winter tires mean FAR more than AWD vs FWD on snowy roads. Well worth the investment for Northern drivers.

Yes. Considering the limited benefit AWD has under most conditions vs its cost in initial purchase price and ongoing fuel economy, it makes more sense to equip a car with the proper tire for the season.

Runningbum: Do a lot of people have a set of winter tires? I've thought about getting a set, mounted on wheels, so I could swap them myself. We don't have too much winter here, but we can, and when we do driving in the mountains it can be difficult. In the past 10 years I recall a 30" snow and at least two 20" snow storms, plus plenty of lower totals, sometimes mixed with ice. But the majority of the time it's clear and I could easily be driving in 50 degree weather between snows, and I read that snow tires don't last long on warmer roads. The plows do tend to clear the roads pretty quickly after storms but that can leave a layer of packed snow/ice occasionally.

When I was on the lobster shift and commuting 40+ miles each way into a rural area, I always had winter tires because the plows usually ceased operations an hour or two before I headed for home. Many nights I would drive home in several inches of snow and slush.

Under the conditions you describe I'd look for an all-season tire with demonstrated superiority in light snow. And if you don't need to go out in a winter storm, stay home.

 

[RunningBum]

Under the conditions you describe I'd look for an all-season tire with demonstrated superiority in light snow. And if you don't need to go out in a winter storm, stay home.

If it weren't for skiing, I would stay home. But I can't miss a powder day! I try to stay home otherwise, but I have been caught a few times. It's the combination of steep hills and ice that gives me the most worry. I've got Michelin Premier A/S tires now, but they are only ok on ice.

The cost is also reduced by putting less wear on my other tires. I think I'm going to do it.

 

[travelover]

Do a lot of people have a set of winter tires? .......

Here in greater Portlandia, there is almost never enough snow to justify snow tires, indeed snow tires are worse for traction in wet and dry conditions and wear fast. But we do occasionally drive over the mountains in winter. To make DW happy, we bought a set of snow tires and rims and I dutifully install them before planned mountain excursions. PITA

 

[Zathras]

I’ve always found winter tires on a 2WD vehicle to be superior to an AWD vehicle with all season tires.
Please note, I don’t do any mountain driving.

 

[RunningBum]

Here in greater Portlandia, there is almost never enough snow to justify snow tires, indeed snow tires are worse for traction in wet and dry conditions and wear fast. But we do occasionally drive over the mountains in winter. To make DW happy, we bought a set of snow tires and rims and I dutifully install them before planned mountain excursions. PITA

Yeah, that gives me pause too. But I feel like conditions are so much worse on ice without snow tires than on wet and dry with them. From what I've read, the Michelin X-Ice Xi3 is better on dry than most snow tires, notably Blizzaks. Still thinking.