Subaru WRX Forum banner

Consumer Reports article on AWD

8K views 31 replies 13 participants last post by  Sasquatch 
#1 · (Edited)
Many of you may already know much of this this info. AWD does not make you invincible in the slick stuff. Tires are far more important.

This may be of help for those new to AWD and trying to decide between all season and dedicated winter tires. Read on:

http://www.consumerreports.org/cro/magazine/2015/09/do-you-really-need-awd-in-the-snow/index.htm

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Forty-one percent of all weather-related car crashes on U.S. roads are due to conditions involving snow, sleet, ice, and slush. That’s pretty sobering when you consider that those conditions usually exist during just a few months of the year. Accidents caused by winter weather result in 150,000 injuries and 2,000 deaths each year, on average, according to a study by the Federal Highway Administration.

Little wonder, then, that car manufacturers trumpet all-wheel drive as a safety shield against inclement conditions. Consumers are inundated with that marketing message, and all-wheel drive is perceived as a must-have for many car buyers. It’s a key reason SUVs are now the top-selling segment of the auto market.

But can all-wheel drive really save you when the weather turns ugly? It provides some benefit, but it may be insufficient to get you through a grueling storm.

All-wheel drive is about getting your car moving from a dead stop—not about braking or steering—and you should be aware of its limitations.

Through weeks of driving in snowy, unplowed conditions at Consumer Reports’ 327-acre test center in Connecticut, we found that all-wheel drive didn’t aid in braking or in certain cornering situations. Our evaluations conclusively showed that using winter tires matters more than having all-wheel drive in many situations, and that the difference on snow and ice can be significant.

We realize that swapping and storing tires twice per year is a nuisance. And in places where street plowing is thorough, you can probably get by with all-season tires that are in good condition.
 
See less See more
#2 · (Edited)
Do you rely on AWD for winter driving?

All-wheel drive is far better than two-wheel drive when it comes to driving on slick surfaces where you need serious traction to get going, such as a snowy uphill driveway. But our tests found that all-wheel drive by itself won’t help if you’re heading too fast toward a sudden sharp curve on a snowy night.

That’s an important point for people who overestimate the capability of their all-wheel-drive vehicle. We’ve all seen them, zipping past us in blizzards with their illusory cloak of invincibility.

Don’t be one of those guys—unless you want to risk a crash or find yourself stranded far from civilization.

Our test-track observations lead us to advise that using snow tires provides the best grip and assurance for going, stopping, and cornering no matter what you drive: all-wheel drive, front-drive, or rear-drive. And buying winter tires for a front-drive car will cost far less than the several-thousand-dollar premium you’ll pay for all-wheel drive.

Enhancements like electronic stability control—standard on every new car since 2012—also help two-wheel-drive vehicles maintain control, at least up to a point.

What did our tests show?

We conducted braking tests in an all-wheel-drive 2015 Honda CR-V, the best-selling compact crossover, with its original all-season tires, then with winter tires. The differences in stopping distances were considerable.

On a different day under different snow conditions, we did braking tests pitting the CR-V against a Toyota Camry, both rolling on new winter tires. The front-drive Camry did just as well as the AWD Honda, both stopping from 60 mph in about 300 feet.

As for handling, we found that some of the all-wheel-drive vehicles in our fleet struggled to stay on course when equipped with all-season tires—even in the hands of our professional drivers. A couple of the vehicles even plowed straight through corners and off the track.

If you live in a place that gets frequent snow storms, an all-wheel-drive vehicle with winter tires will be very capable. And some AWD systems function better than others in terms of helping drivers get traction.

But most AWD drivers don’t think of adding winter tires. According to our survey of 54,295 subscribers who drove AWD or 4WD vehicles in the snow for more than six days last winter, less than 15 percent equipped their vehicles with winter tires. The rest kept rolling on their all-season tires and took their chances.

At Consumer Reports, we strongly recommend buying four winter tires for whatever vehicle you drive.
 

Attachments

  • Like
Reactions: TheJ
#3 · (Edited)
All-Wheel Drive


All-wheel drive is a lighter-duty system used for cars and car-based SUVs. AWD systems operate continuously, and they automatically vary power delivery to the front and rear wheels when needed. Some systems remain in front- or rear-wheel-drive mode until slip is detected, then power is routed to all four wheels. Other systems send power to all four wheels continuously.

Good for: Seamless acceleration in slippery conditions. Needs no driver intervention to engage.

Drawbacks: Can’t improve braking or cornering performance in snow; lacks heavy-towing ability; lacks a low range for slow-crawl situations; fuel economy suffers; and there’s a price premium compared with front-drive cars.


Four-Wheel Drive


This refers to the heavy-duty drivetrain components found in pickup trucks and truck-based SUVs. The truck usually sends power to the rear wheels, and the driver engages four-wheel drive with a dashboard knob or button, which sends power in equal proportion to the front and rear axles. Most current SUVs and some pickups have a permanent or “auto” 4WD mode.

Good for: Grunt work like hauling a boat trailer up a launch ramp. Most systems have a low range and locking differentials for extreme terrain.

Drawbacks: Can’t improve braking or cornering performance in snow; driving in locked 4WD mode on clear roads can damage the driveline; and there’s a wider turning circle in 4WD mode.


Front-Wheel Drive


Used in most cars, minivans, and wagons, front-wheel-drive systems send engine power to the two front wheels. The drive shaft doesn’t extend to the rear of the car, leaving more room for rear-seat and trunk space. Traction control limits wheel spin in certain inclement conditions.

Good for: Good traction in most driving situations. And it doesn’t carry the price premium of all-wheel drive. It’s also better than rear-wheel drive on slippery roads because there’s more weight on the front wheels, which propel and steer the car.

Drawbacks: If the road is too snowy or icy, the front wheels will slip and you’ll be stuck. Winter tires are recommended for snowy conditions.


Rear-Wheel Drive


This system places less demand on the front wheels, freeing them to be used primarily for steering. It’s often used in basic pickups and traditional truck-based SUVs that are designed to handle towing and other chores. Traction control can help improve the performance of those vehicles as well. Rear-wheel drive is also the preferred setup for sports cars and high-performance sedans because of its contribution to ideal weight distribution, which aids in handling.

Good for: Handling balance and cornering in dry conditions.

Drawbacks: If the road is too snowy or icy, the rear wheels will slip and you’ll get stuck. Rear-drive cars tend to spin out in snowy or icy conditions. Winter tires are recommended.
 
#5 ·
You are quite welcome.

There have been countless threads started on these subjects over my nearly 12 years here. This article covers nearly all of it.

I copied and posted all of the text in the event the link goes dead at some point.
 
#9 ·
What would really be nice is some kind of friction sensor which could tell me what the condition of the road ahead of me will be. It is very challenging to anticipate rapidly changing grip conditions (in spite of the "bridge ices before road" signs).

At some point, vehicle-to-vehicle communication will help inform subsequent drivers down a given path, but it will be tough for the first person.
 
#10 ·
Drove mom's impreza with all seasons and also drove my WRX with Altimax Artic snows back-to-back today in first good snow/cold (0) we had in north central OH today. Night and Day. Snow tires much better in all ways. Impreza on all-seasons not terrible but snows so much better. Also have to say Subaru's traction control systems work great! Both cars much more "in control" with TC on. When I turned them off, cars were way fun but also all over the place slipping and powersliding. Rear wheel drivers are the most fun in snow if one wants to slip/slide/donut around though.
 
#11 · (Edited)
Their definitions of all- and four-wheel drive are popular but I don't see why that would make them correct. In fact significant manufacturers have used the terms in the opposite manner.

A 4WD or 4X4 Ford:



A 4WD Lancia:



A 4X4 Ferrari:



Example of an "AWD" car with a transfer case: The Chrysler D platform. If you ever owned a DSM, I'M VERY SORRY!!! Nobody should have go to through that. Anyway, DSMs were "AWD" in internet or marketing speak, yet they not only had a transfer case according to the manufacturer, but also according to the US goverment -- the later forced the former to recall the cars due to a leak in that same transfer case that of course should not have been there since the car was AWD, not 4WD. Um... Anyway, I think I've made my point: the definitions given do not reflect reality. Since definitions must follow reality because reality will not change to follow definitions, then the definitions don't stand. I'm not posting a picture of a DSM because I consider such an act offensive.

Consumer Reports and most internet forum posters would call these cars "AWD" and post corrections. I don't think anyone at Ford or Fiat cared at the time... And I'll leave it to the reader's imagination to figure out with whom I'd side on the issue...
 
#12 · (Edited)
AWD is MUCH more than the article claims because of electronic differentials and controlled braking added to the software.

The most important feature is the person sitting in the driver seat.


-------------------------------------
"One cannot awaken a man who pretends to be asleep."
 
#14 ·
Obviously, tires matter but TRACTION will undoubtedly be greater with AWD vs FWD or RWD.


-------------------------------------
"One cannot awaken a man who pretends to be asleep."
 
#16 ·
Yes, friction... Mu * Normal force of the contact patch.

Times two...


-------------------------------------
"One cannot awaken a man who pretends to be asleep."
 
#17 ·
So what? Good you can stomp the throttle at speed and be marginally less likely to spin the tires.

A tire can only offer so much friction if all of your tires are busy providing forward movement less is available for lateral grip. It causes a very dangerous situation because it seemingly masks errors because the entire car slides sideways instead of just the back, or in the case of fwd you have no steering.

Sent from my Nexus 6 using Tapatalk
 
#18 ·
So you know better than Audi, Subaru, Porsche and all the rest.

Yes, I have twice the TRACTION of a RWD/FWD and whatever traction is available per tire is still TWICE WHATEVER IS AVAILABLE TO RWD/FWD.


-------------------------------------
"One cannot awaken a man who pretends to be asleep."
 
#20 ·
So WORLD RALLY CARS - turbo AWD and turbo FWD.
Which do YOU believe are quicker across stages - especially snow?

Have a nice day...


-------------------------------------
"One cannot awaken a man who pretends to be asleep."
 
#21 ·
What does that have to do with adding traction? Nothing. Rally cars slide through corners so they can use the the big advantage. Traction on launching.

The only ways to add traction is add tires, add weight, or increase contact patch. Any other argument is void

Sent from my Nexus 6 using Tapatalk
 
#22 · (Edited)
Uhhh, traction is traction. It's rather obvious what's going on which is why I asked you.

You erroneously equate "traction" to straight line acceleration only.

Nothing could be any further than the truth.

Acceleration is acceleration: Lateral,
Linear positive or Linear negative.

Traction is traction and AWD *will punish it's tires less* than a 2WD vehicle.

Why?

Because it's putting the power down out of the corners in a much better balanced manner - *ALL* WHEEL DRIVE. (Each doing what it can with the traction available).

And, of course, a hard launch is better with an AWD system but the power to weight ratio is also worse so on dry pavement it gets the hole shot but that's the only advantage it will have in a straight line sprint in event.

Vehicle Dynamics, bro...


-------------------------------------
"One cannot awaken a man who pretends to be asleep."
 
#23 ·
Yeah I understand vehicle dynamics. You clearly and obviously do not. It doesn't matter how many tires you have driving you are not adding friction between the tire and the ground.

This argument is stupid, and every year as I see all these inferior 2wd vehicles cruise past awd cars and SUVs off the side of the road I'll remember how correct you are.

Sent from my Nexus 6 using Tapatalk
 
#24 · (Edited)
Try reading for comprehension - or at least be honest in your comments.


You're telling me on one hand that AWD helps and on the other hand it does not.

Which is it?

I commented that the most important part of the system is sitting in the driver seat and we both know (well, I do) that your average driver is no damned driver in any sense if the word so seeing ANY vehicle parked on a curb doesn't tell me much of anything about driveline layout.


You also failed to ADEQUATELY address (for me) the question I asked above. Rally car: AWD vs. FWD which is quicker on a sippers surface?

You intimated that lateral grip/traction was "non-existent" as you stated that "sliding" around the corners magically made my argument disappear.

I provided you the simple equation of Normal Force and mu (Coefficient of Friction). It applies to *ALL* forms of vehicle acceleration. Matters not if I'm doing a lot of sliding - friction is still there or the car simply continues to slide off the outside corner of the turn, no?

You DID acknowledge that AWD was good for accelerating the vehicle from a stop. And it surely can be.

You stated that all of the tractive effort was being used to maintain velocity (No...) so that it would have little ability to negotiate a turn... Maybe if one were spinning tires while trying to negotiate a hill.


----------------------------------
"One cannot awaken a man who pretends to be asleep."
 
#25 · (Edited)
Since you are just digging for an argument fine.

My stance as not changed. Awd helps on launching and straight line movement only. Period. No if ands or buts. It does not add traction in any way.

The reason a rally car is better in awd is because they take advantage of the straight line traction. They don't slide through corners because of all the added grip. They do it because they can line up exactly to the exit and give it throttle. They go sideways easily because of the awd system where fwd wants to kill your steering. Again awd doesnt add any more grip than the tires are able to provide.

When you are using the available friction of a tire to say propel the vehicle forward then there is less grip to propel the vehicle sideways such as around a corner. This exact function is what causes a front drive to loose steering and a rwd car to over steer. An awd car just slides sideways. That doesn't mean the awd system added anything it means you have the appearance of increased cornering.

Awd has negligible impact anywhere but going from a standing start, or accelerating straight. Tires are the driving force. They have all the impact.

Sent from my Nexus 6 using Tapatalk
 
#26 ·
What I SHOULD have stated - and I concede your point (you're CORRECT) it's the linear component of the tractive effort it provides accelerating OUT of corners.

Good discussion!

[emoji1360]


-------------------------------------
"One cannot awaken a man who pretends to be asleep."
 
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top