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4WD and AWD systems explained

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Comments

  • wwestwwest Member Posts: 10,706
    Insurance companies are currently counter-motivated, the more money they lay out to fix you and your car the more money they make.

    But where do we get the funding for the R&D and then to equip each and every High School driving class with a simulator?

    Damn Good PR for the insurance companies!!!

    Most states regulate the insurance industries, basically limiting them to a certain percentage of profit for each $ spent. Obviously the more they spent to fix you and your car the higher the absolute $ value of that % limit.

    Counter-modivation....they WANT us to have more accidents.

    Get the state's regulating agencies to allow a higher % of profit for each level that their, the insurance company's, actions reduce the automotive accident and death rate.

    I grew up on a farm in Arkansas driving mules and then tractors and had no idea about foul weather driving. The first thing the USAF did was put me out on a vacant section of an icy ramp in NH to learn what driving in foul weather was all about.
  • ateixeiraateixeira Member Posts: 72,587
    I love a good conspiracy theory. :-)

    GEICO bought LIDAR guns and gave them to the MD police. The police then wrote tickets, and GEICO raised the rates of their own policy holders, who suddenly became riskier drivers out of nowhere.

    So they're definitely out for the money.

    -juice
  • wwestwwest Member Posts: 10,706
    They could always say they did that to make our highways safer.
  • email77email77 Member Posts: 27
    Hi I own a 2003 Nissan Murano SE AWD it had a switch "AWD LOCK" tell me when should I use this switch, where I live have a lot of snow and ice. do I need to use it in the whole winter, some said once the speed is over 80KH it goes off. I also own a ML320 4 wheel drive it don't have the switch, is that mean it is auto 4X4.
  • ateixeiraateixeira Member Posts: 72,587
    ...and they do say that.

    The Murano is intended for part-time use since it has no center differential (I'm almost certain about that), so do not leave it on all winter. It should be used on slippery surfaces only, so basically when there is snow on the ground, or while you are on gravel or sand, or other loose surfaces.

    The rest of the time, it engages automatically, so don't worry in situations were traction varies. Use the button only when you are certain you can make use of 4-wheel traction to avoid binding.

    The ML is totally different. It has 3 open differentials (front, center, and rear) and can handle full-time use. In fact it does send power to both axles full-time, so there is no button needed.

    -juice
  • adp3adp3 Member Posts: 446
    Is it just a downright stupid idea, for a driver in the SF Bay Area, to put different tires on his SUV (or AWD wagon - XC90) for the winter months than he uses the other 9 months fo the year? Maybe use a tire that gives better mileage and "every day" performance from March-November, but put some deeper tread tires on for December-February to improve performance in snow country. I know this used to be common in other parts of the world, but I've been out here so long that I don't even know if it's done any more.
  • paisanpaisan Member Posts: 21,181
    On how often he or she is gonna hit that snow country. I live in NYC and use all-seasons in the winter and summer tires in the spring/summer/fall. We don't get enough snow (except this year) to warrant a set of snow tires.

    -mike
  • ateixeiraateixeira Member Posts: 72,587
    I agree - it isn't stupid to get a set of snows if it prevents you from crashing your nice vehicle, especially when a full set might represent just 2% of your total investment.

    I'd say if you venture up to Tahoe in the snow season, and ski a lot, or just travel off the beaten path, then by all means, get snows.

    -juice
  • wwestwwest Member Posts: 10,706
    It seems to me very likely that snow tires, ANY (most) winter tire, will give less roadbed traction on dry or wet pavement than ANY summer only tire.

    Even here on the eastside of Seattle, and including the fact that I often travel over snow packed mountain passes in the wintertime, I stay with summer tires year-round. Quieter, more comfortable, and more sticktion, in the more predominant roadbed environment.

    But I do keep a set of snowchains in the car for those times when true wintertime traction is desired.
  • paisanpaisan Member Posts: 21,181
    The compound of summer tires is for just that. Summer. Basically if you run summer tires in the winter you risk loosing control because the compound of the rubber is not going to allow them to stick to cold pavement. I'd strongly suggest getting some all-season for the winter if you don't go for snows.

    -mike
  • wwestwwest Member Posts: 10,706
    Rubber compound....
  • sebring95sebring95 Member Posts: 3,241
    I agree with Paisan, the compound makes a big difference. Obviously tread pattern and such weighs in, but the inital main characteristic is the compound. Good articles at tirerack.com

    All-seasons are a compromise, but they're more than adequate for most folks. Obviously anyone wanting to maximize traction one way or the other would pick the best tool for the job. All-season for cars and all-terrains for SUV/Trucks are the compromise tires. All-seasons on a SUV/Truck excell at on-road fair weather driving, and conversely is usually what most suv/trucks are sold with. My Jeep came with all-seasons and they pretty much did nothing well IMHO.

    Example: I now run all-terrains on my Jeep because I do some off-roading and routinely see snow, but also do a lot of highway driving. All-terrains are the best compromise for what I do. If I wanted to maximize traction in all circumstances, I'd have a set of M/T's (mud terrains) for off-roading, set of snow tires for winter, and would likely go with all-seasons for on-road summer driving. So far the Michelin A/T's I'm running have done just fine in light off-roading, 20" of snow, and feel pretty good on the highway.
  • paisanpaisan Member Posts: 21,181
    I have to agree with what sebring is saying here. I also have an SUV and go with the ATs for an all-around tire.

    -mike
  • wwestwwest Member Posts: 10,706
    Does anyone know of any testing having been done on wet and dry roadbeds for roadbed "sticktion" with summer tires versus ANY all-season or wintertime tire?

    It seems likely to me that for most of us the need for all-season or winter tires is well below 1%, even in wintertime. If 99.99% of the time summer ties offer better sticktion then are we needlessly putting ourselves at greater risk with winter tires?
  • paisanpaisan Member Posts: 21,181
    How many times do we have to tell you that in cold temps the compound of the summer tires won't stick, not to mention summer tires don't have nearly the same wet traction as all-seasons... Some people just don't get it.

    -mike
  • wwestwwest Member Posts: 10,706
    Anything anywhere supporting your point about rubber compounds, looked everywhere. I would think that something of this serious nature would be well documented.

    I think you would agree that summer tires definitely put more rubber to the road, now the question becomes what is the adhesion coefficient of the summer rubber compounds vs "winter".
  • paisanpaisan Member Posts: 21,181
    R-compounds on the street? Cause there isn't enough heat to make em stick. Same exact thing is the case with summer v. all-season tires.

    Of course if you live in a warm climate it's not a big deal.

    Heres a few links...
    http://www.talontire.com/wintertips.html
    http://tirerack.com/winter/tech/faqs.html
    http://www.canadiandriver.com/articles/cml/winter_tires.htm

    -mike
  • wwestwwest Member Posts: 10,706
    is an interesting referral since they plainly state that their winter tires DO NOT have the corning ability of their summer tires on wet or dry roadbeds.
  • paisanpaisan Member Posts: 21,181
    That the snows would handle better on dry. All-seasons however WILL due to their compound being more adhesive on COLD pavement. Hey I don't care if you smack up your car, just trying to help you out here.

    -mike
  • wwestwwest Member Posts: 10,706
    And by the way some of your referrals state that the level of COLD is -15F and below before the differing rubber compounds come into play. I haven't seen those kind of temperatures since I left MT, and even then it wasn't for more than a few days in a row.

    Also, ALL of your referrals, and many others, openly disparage A/S tires since there is no agreed industry standard for just exactly what is required to use the label.
  • nra1871nra1871 Member Posts: 26
    I have a 4wd pickup, and you won't catch me in the winter without my snow tires on. There is no contest in snowy or icy conditions as to which sticks better.
    Is this the same wwest who in another thread was insisting that you never need to change your transmission fluid or coolant?
  • wwestwwest Member Posts: 10,706
    I'm not saying that snowtires don't have better traction in snow. What I have said is that MOST of us don't encounter snow on the roadbed often enough to justify the loss of safe operation on dry or wet roadbeds by using snowtires continuously during the winter months.

    I spent a few winters in north central MT, and remember even using winter tires with embedded walnut shells to improve traction on icy surfaces.

    But that was MT.

    Here in the Seattle area that type of adverse weather is a real rarity, unless you choose to go to "it" in the nearby mountains that is. The information I get from the tire companies is that summer tires offer better grip on wet or dry pavement than do snowtires. Someone has argued that the rubber compound in snowtires make them grip better that summer tires at lower temperatures. The only confirmation I could find of that point was that it only applies at -15F and below. Certainly not a roadbed temperature most of us encounter very often, not even in MT.

    To be fair to all, I have Michelin cross terrains on my RX, but only becuase I couldn't find a nice quiet, comfortable and smooth-running summer passenger tire in the correct size.
  • paisanpaisan Member Posts: 21,181
    I really think you should run some nice R-compounds. They'll surely stick even BETTER than the summer tires. :)

    -mike
  • kenskens Member Posts: 5,869
    Dedicated winter tires in the SF Bay Area? It depends on what you do.

    For driving just in the SF Bay Area, snow tires are not a good idea. Even if you happen to live about the 1000 ft. level that gets a dusting of snow maybe once a year, it's way overkill. The softer compounds on the snow tires will wear out quickly in our mild winters.

    If you travel to Tahoe and pretty much go up I-80 or I-50 straight to the resorts and have AWD/4WD, then all-seasons will probably offer the best cost-performance. While dedicated winter tires will provide better traction in snow/ice, the major roads to Tahoe get cleared often enough that all-seasons won't be a problem. Also CHP is quite conservative and will shut down the passes before going to R-3 conditions. In this case, you would need chains regardless.

    If you do go off the beaten path at Tahoe or any part of the Sierras, then dedicated winter tires may make sense. You'll still need to carry chains, however in case you come by a CHP chain control.

    Ken
  • wwestwwest Member Posts: 10,706
    Then why bother with anything but summer tires?
  • pschreckpschreck Member Posts: 524
    Anybody out there want to try to explain how the adjustable center differential on the WRX STi works?
  • smily1smily1 Member Posts: 104
    I have a 98 V8 AWD explorder with 62k miles. I am having vibration at sharp slow speed turns. It feels like my viscous coupler is frozen...is this a problem with these and is there any documented information to how these go bad??
  • pschreckpschreck Member Posts: 524
    You might want to try posting to the Ford Explorer board. Good luck.
  • smily1smily1 Member Posts: 104
    Thanks, I did. I am not getting the information about the viscous coupling that Im looking for. I know there has to be some AWD buffs here.
  • ateixeiraateixeira Member Posts: 72,587
    Subies with the viscous coupling are extremely sensitive to variations in tire diameter. Make sure the tires are evenly worn, and the pressures are the same.

    I have not seen specific complaints about the Explorer's system. You may want to ask Mountaineer owners, since more of those had that system.

    -juice
  • tidestertidester Member Posts: 10,059
    Obsessive/compulsive is the preferred term and it's less crude. :-)

    tidester, host
  • smily1smily1 Member Posts: 104
    My apologies. Deleted. Re stated below:

    thanks ateixeira

    I have been very meticulous about the alignment and tire pressure. All is good there...all same size and wearing good. I will give the mountain folks a shot.
  • ace1000ace1000 Member Posts: 151
    With an AWD in California, don't you have to carry two sets of chains in case of a R-3 condition, or can some AWD systems take chains just on two of the wheels?
  • derf11derf11 Member Posts: 3
    What about A/T tires? I was under the impression that softer tires get better traction and that is why they wear out sooner. b F Goodrich vs Mich...

    Is this true? I don;t care about the expense. I want to stick to the road.

    1/2 season nice weahter, 1/2 bad.

    N.E. USA
  • capriracercapriracer Member Posts: 907
    Everything else being equal, generally, the softer the tread compound, the more the DRY traction. Somewhat true for wet traction and less true for snow traction.

    But when we start to compare all terrain tires with all season tires, the tread pattern can completely completely change that equation, particularly wet and snow traction.

    Also when you try to compare different brands of tires, this "softness" equation probably works within a brand and may not between brands. The reason is that every manufacturer has its own way of compounding and curing the rubber, and those differences translate into differences in hardness.

    Also it is generally true, that all terrain tires are compounded with harder tread compounds to resist chipping and chunking that you get on unimproved road surfaces.

    But be careful - Folks will use the terms "all terrain" and "touring" rather freely and it is difficult to make statements that are universally true - generalizations, at best.

    Hope this helps.
  • paisanpaisan Member Posts: 21,181
    Tell us more about your driving, your vehicle, etc.

    Is it on-road?
    Is it off-road?
    Is it Snow covered? if yes, what kind of snow?
    Is it Ice?
    Is it Rain?
    Is it rock crawling?
    Is it Highway?
    Is it Dry?
    Etc. etc.

    What vehicle?

    -mike
  • sibiryaksibiryak Member Posts: 5
    Edmuns gives different prices for 2004 Highlanders v6 w/3rd seat 4WD v. 2004 Highlanders v6 w/3rd seat AWD (the latter is $1000 more). However, when I look on all Toyota sites they only differentiate between 2WD and 4WD, but not the subsets of 4WD (assuming there are any). Are there really 4WD and AWD 2004 Highlanders? If yes, what is the difference? I always thought 4WD was better than AWD, but it does not seem to be the case with Highlander becuase you pay more for AWD than 4WD. I am totally confused!?
  • ateixeiraateixeira Member Posts: 72,587
    It's AWD, there is only one system I believe. Are you sure you're not comparing a 2003 to a 2004? If not, I'd e-mail Edmunds to let them know they need to make a correction.

    If you want 4WD, look at a 4Runner. Those can lock the center differential and have a low range.

    -juice
  • sibiryaksibiryak Member Posts: 5
    On the back door of my Highlander there is a sign "4WD"???
  • ateixeiraateixeira Member Posts: 72,587
    Well, that's the marketing team's decision. They probably thought it would sell more, perhaps have a tough-truck image?

    It's not - it's car based and the system is AWD by just about everyone's definition.

    -juice
  • haropharop Member Posts: 59
    Finally after reading lots of usefull links
    on the net, I am ready to ask some questions
    about my wife's future vehicle :)

    1. Is it true you cannot drive on 4H mode
    on dry road?
    Local dealers(not only ford, but toyota-sequoia
    and nissan-armada) all claim it is OK to drive
    their vehicle in 4H mode. But after reading all
    this, I think it is not true.
    Please someone conform for Expy.

    2. Is there any speed limit for 4H ?

    3. When the A4WD mode activates 4x4, is it 4H, 4L
    or something different, say AWD?

    4. How big is the difference between A4WD mode,
    and full time AWD cars(there are no AWD trucks!
    I guess).

    I understand different cars have different 4x4
    systems, but I will be more interested about Ford
    Expedition 2003 (or 2004).
    Thanks
  • paisanpaisan Member Posts: 21,181
    On the Expedition the 4-Hi mode cannot be used on dry pavement as it locks you in a 50/50 torque split. With the A4wd mode is RWD until it detects a wheel spinning, then it will set torque to 50/50 split, this mode can be used on dry pavement because it only engages your 4-Hi system when there is slippage.

    Generally you can shift to 4Hi up to ~60mph and there is no limit on how fast you can go in 4-hi once it's engaged.

    The systems on the Sequoia and Armada allow 4-hi to be active on dry pavements as it is a system similar to the auto4wd or is an AWD system.

    IMHO a system that puts *some* torque to both axles is far better than an "auto-engaging" system because it PREVENTS slippage rather than engaging 4wd AFTER slippage has occurred.

    -mike
  • haropharop Member Posts: 59
    Thanks Mike for detailed explanatoin. It seems to me I should look for Sequoia or Armada, but anyhow there are many pros and cons.

    Now back to 4x4 mode for the sake of this forum.

    So, in A4WD mode when it detects a wheel spinning, then it will engage 4H, and after that it will continue until there is no spinning, and then it will go back to RWD mode. Now, when turning on dry pavement, I guess there is some spinning, i.e. not all wheels have same spinning. In this case A4WD must activate 4H. But this is contradiction.
    Please correct me if I am wrong.

    To me, it seems 4H being as AWD is better choice.
    If you are moving, then you can do it in AWD mode.
    If you are stuck, then you can use 4L to get
    unstuck. Then why locked 4H is needed at all.
    I know, I am just new to 4x4s, but anyhow I am
    trying to understand as much as possible.

    -haro
  • paisanpaisan Member Posts: 21,181
    Well that's the thing, there needs to be spinning for X amount of time in order for it to activate, so a simple turn, would not be enough to induce the 4-Hi engagement.

    On my Trooper with AWD/4wd, if you have it in AWD mode, it will do an initial torque split of 15/85 and then vary it up to 50/50 depending on slippage. Then I can lock it in 50/50-Low Range if I am in the real nasty stuff. Some of the other more hard core off-roaders like 4-hi locked at 50/50 but I've done some difficult trails and never gotten stuck with my TOD system. The only place I'd want locked 4-Hi, is on the beach in loose sand. That's where you want some momentum (4-hi) and locked at 50/50.

    -mike
  • sebring95sebring95 Member Posts: 3,241
    Well that's the thing, there needs to be spinning for X amount of time in order for it to activate, so a simple turn, would not be enough to induce the 4-Hi engagement.

    That time period appears to be "very fast", however you'd like to measure that:) I did some testing on my Tahoe this last winter between "auto" mode (which sounds similar to the "A4wd" mode you were discussing above), the "4-hi" mode and "2wd" mode. My test was pulling out of my driveway which is a gradual up-hill climb. From sitting idle at the end of my drive, I found the only noticable difference between the settings was if I was really hammering the gas. Starting and stopping with normal accelerator input provided no noticable spinning. The only way I could truely get ahead of the "auto" system was to accelerate normally into the road and half-way through the turn floor the pedal. Doing this caused my tail to swing a couple feet before the front dug-in enough to straighten me out. In 2wd I could get going (I've got the limited slip diff) fairly well although you had to really watch the throttle input. Flooring the pedal through the turn would kick the truck sideways and I let off before doing a 180.

    Another test I did was up an extremely steep packed snow road. I drove up the hill in 4wd with no problems and did my testing on the way down just to be safe. Half-way down I crawled to an ABS assisted stop. Put the truck in reverse (still in "4-hi"), and slowly backed up the hill with no noticable slipping. Did this again with a heavy throttle and spun the tires but climbed straight up again. Next was "auto" mode which with normal throttle backed straight up the same as "4-hi". Flooring the pedal spun the tires and the rear kicked out very slightly but then went straight up again. In "2wd" I basically just spun and the rear slowly slid sideways regardless of how easy I throttled it. With heavy throttle it tried to climb and kicked back and forth but was moving. It would have been a long trip to the top.

    Last week we were in Maine during heavy rains. I put the truck in "Auto" as we drove around town and I could feel the front axles engaging as we pulled into sharp parking spots and pulled out onto the narrow roads. I don't think it takes much slippage for the center diff to engage.

    I like the option of disengaging the 4wd systems and running in 2wd. While I think the AWD system might have some advantages, the real-world difference is likely minimal. You get a lot of wear and tear and drive-line drag running both axles constantly when it's essentially not needed. Running the 900 mile trip in 2wd we averaged 20mpg on the way up with five passengers and way too much luggage. Coming back I was pullng a trailer but still got 15mpg. I'm sure an AWD system would zap my mileage at least a couple mpg.

    This is my opinion as far as a vehicle used for multiple situations. Obviously heavy off-roading would require a different set-up, but for all around use I like the option of running various way, most importantly in 2wd the majority of the time. For off-road I'll take a standard 4x4 system with lockers on both ends.
  • paisanpaisan Member Posts: 21,181
    I usually run my Trooper in 2wd as well. Unless it's wet, or variable conditions. I just prefer a system that puts some power to the front axle when engaged v. none to the front axles. Love the point-shoot driveability of that. The auto-engaging systems are a bit slow for my particular driving style. But they are better than nothing though.

    -mike
  • denali856denali856 Member Posts: 118
    Just curious....
  • jhs70jhs70 Member Posts: 213
    Wife used 4wd one day last week in the snow but didn't turn it off for another two days. I won't go into how it happened, it just did. I thought the 4wd would be ruined (this is on an 02 gmc envoy slt) but this weekend we had a lot of snow and it seemed to work ok. I was surprised (there are no overt signs of damage that I can tell).

    Can someone out there tell me what to do at this point, if anything?

    Thanks.
  • ateixeiraateixeira Member Posts: 72,587
    The tires scrub off any difference in speed. I'd just inspect them to make sure you didn't get any unnecessary wear. Maybe rotate them if you're close to your next scheduled rotation.

    Make sure the fluids get done at the next 30k/60k/90k interval, too.

    -juice
  • paisanpaisan Member Posts: 21,181
    Any damage will be internal and probably is ok, so long as it wasn't for extended driving in the city on completely dry roads.

    Definitely get the fluids changed though.

    -mike
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