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Toyota 4WD systems explained

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  • wwestwwest Posts: 10,706
    should NEVER be downshifted if one suspects a slippery roadbed. Engine braking on FWD vehicles as a result of downshifting, or even lifting the throttle completely, can result in complete loss of roadbed traction at the drive wheels which just happen to also be the way you maintain directional control of the vehicle.

     

    With experience it can be done safely with RWD vehicles since loss of directional control will not be simultaneous with loss of traction at the driven wheels.

     

    The latter is also why RWD and/or rear torque biased AWD is inherently safer, MUCH safer, on adverse roadbed conditions than FWD or front torque biased AWD.
  • serranotserranot Posts: 113
    I have been reading the above discussion, and it is obvious that definitions are again getting in the way.

     

    Tlcman is using "part-time" as if there is a center differential that can be either locked or unlocked. That is not my definition of a part-time system. Part-time 4wd is a front and rear driveline powered by a transfer case. There is no center differential. This is like the systems on many pickups and Jeep Wrangler.

     

    The full-time 4wd and AWD systems have some type of system to account for differing driveline speeds, be it a viscous coupling, electromagnetic clutch, center differential, or electronic diff (like Acura).

     

    So all of the above comments seem correct from a certain point of view. I agree with Qualitynut's original assertion--the average Joe is unfamiliar when he/she may properly and safely use a part-time 4wd system because of a lack of understanding of the dynamics involved. Like Tlcman has said, though, put a center diff in there and it takes away the issues.

     

    Regards,

    Tom
  • tlcmantlcman Posts: 220
    right thats what I was getting to... in some wierd way... RWD is actualy more dangerous on Icy roads and this is proven by Michelen and other tyre companys, reason being that if your rear steps out due to down shift, rapid accel or what ever, if it steps out the average joe driving down the freeway does not have the responses to compensate and steer into the skid, and we all know that over steer is mutch harder to control than understeer. The Front wheel drive car will loose traction at the front not stepping out but ratehr pushng the tyres (turning situation) causing understeer, which is very easy to correct for. So in that sence i dissagree with you. Its the same with buying two new tyres, your local tyre shop will recoment putting them on the fron most likly for "better steering abilitys and traction" but this is wrong and is dnagerous, put new wheels on the back of any car and the older ones on the front. The newer tyres can shed water better and will stay in contact with the road more, and if on the rear this will keep your car from over steering if you are say on a curved Highway on-ramp. Now you might understeer but that is easy to correct, so It is mutch safer in winter in a FWD car and always put your 2 new tyres on the rear. Personaly, I like RWD on Ice, people think Im crazy but I know how to control my car and its fun to get a small power slide or a bit of a drift going when turning on to an unused iced over road. Its more fun in my opinion and I have not been in a situation that I could not control yet... knock on wood..
  • wwestwwest Posts: 10,706
    Now tell me just how you recover from understearing/plowing in a FWD vehicle.

     

    Assume the (inexperienced) driver has sensed a bit of understear, followed their natural instincts and lifted the throttle. The roadbed was/is very slippery and the front tires had obviously lost enough traction to significantly reduce lateral control.
  • nedzelnedzel Posts: 787
    Just how do you do that?

     

    I've driven many rear-wheel-drive cars. Countersteering is second nature to me. I can correct for that.

     

    The only thing you can do for understeering is wait it out and hope you get some grip before you hit something...
  • tlcmantlcman Posts: 220
    what my sistuation that I was refering to was a twisted highway on ramp, Nedzel you are not the average driver, you have had experiance with oversteer, I have driven many sportc cars FWD, AWD and RWD I like RWD for the added fun nd involvement that is needed on slipery surfaces, lets remove the icy sisuation on our highway on ramp for this analogy, say you just put two new tyres on the front of your car and the olderones are out back, accelerating and turning say while its raining, your back end steps out, the average driver does not compute or think about this happening, so their reaction time will be longer than that of yours or mine (in my sisters case it was unexistant, resuling in the roll over) you and I would steer into the slid and have a higher chance of regaining control depending on circumastances. An enexperianced driver who reacts slower and maybe hits the brakes or guns the engine (stupid to gun in oversteer unless your steering into it with FWD car, and even then its a last resort) has a lesser chance of a full safe recovery. vehicle moving sideways with velocity could result in a roll over, or a worse acident. Now say you put those new tyres out back, and you are going around the corner same situation but your front eng pushes, most average drivers and me (dono about you) would pull a little back on the accelerator and lighten up on the steerin angle, every time ive understeered in my honda that is what I did and i regained full control in less time and in a safer manner than oversteer step out. Say if you dont regain control on an understeer or oversteer, understeer is safer because your car or SUV is not sliding sideways, thus most cars and suvs are equiped with frontal airbags and only some are equiped with side and fewer with rolling airbags, so your chance of injury is less on understeer. Im not making this up, its taught standard in driving schools in Fort Collins as my son has told me, and I have read an article that Motor Trend has writen about Michlens tyre testing directly connected with this topic I would be glad to look for a link to the story if it exist online.
  • wwestwwest Posts: 10,706
    ..that while there is a recovery technique for RWD overstear, most folks don't know how anyway, so it simply doesn't matter that there is NO recovery technique for understearing.

     

    Did I get that right?

     

    So I guess that means that since I do know how to recover from overstearing I'm one of the lucky ones who can continue to purchase RWD only and possibly thereby extend my life duration.
  • tlcmantlcman Posts: 220
    I dont think you read how I and i believe most recover from understeer, it is a recovery technique for understeer, please read it again

     

    "around the corner same situation but your front eng pushes, most average drivers and me (dono about you) would pull a little back on the accelerator and lighten up on the steerin angle, every time ive understeered in my honda that is what I did and i regained full control in less time and in a safer manner than oversteer step out."

     

    The average driver is not thinking of all of the posibilities while on the highway on ramp so when the rear starts to slide or "step out" It takes them longer to realize what is going on, thus longer to recover and less of chance of a safe recovery. Oversteer causes the backend to swing out which is very dangerous on cars and SUV's which can roll pretty easily. Few cars are equiped with rolling airbags more but still not alot have side airbags, and almost every new car has front airbags now, so an understeer where it can be corrected by lessening the steering angle and not jumping out of, but rather giving less gas to the engine. Doing this I have regained control out of every understeer that I have ever got in with a front wheel drive car. and lest say that you dont recover from the understeer or the oversteer example. Not recovering from an over steer, means that your car/ SUV is sliding sideways, and if its an SUV can roll pretty easily, causing a more severe accident, if you cant regain control on a understeer, then you will hit somting from the front and most cars are designed to take frontal impact, and many have multi stage airbags, its safer than rolling your car, plus if you cant regane control and happen to go off the road, and there are no obsticals then you can still control your car as you play around in the mud trying to come to a stop. Do you understand me now?
  • russlarussla Posts: 74
    in my personal experience,

    it seems the natural response when something wrong happens, is to let up on the throttle,

     

    in an oversteer situation, this helps the car regain composure, as the rears stop spinning (from applied power) and regain traction and fall back in line.

     

    in an understeer situation,when accellerating around a corner, in some front wheel drive cars, letting off on the throttle, very often transfers weight back to the front wheels, giving them add'l traction, and at the same time unweighting the rear, which causes an oversteer situation.

     

    regards
  • tlcmantlcman Posts: 220
    Ive never seen oversteer resulting from corrected understeer, I see what you are saying but when you let up on the throttle you let it regane traction because when you are turning the front wheels already have a strain on them to move the car in that certain direction, when you want to accelerate and turn at the same time you put two forces on the tyre; directional changes, and acceleration. The combination of these and the ammount is what starts understeer, the tyres can not keep traction with the steering angle and the amount of torque that is being put to them, not transfering of weight.
  • Hello everyone. I'm sure this question has already been answered in this forum, but I was unable to locate the answer during my brief search. I purchased the V8 4Runner SR5. I know that the V8 is in 4WD all the time; however, my question is whether the 4WD system on the V8 4Runner is still the same as the V6, just without the option of dis-engaging the 4WD. I know several other vehicles (like the Honda CR-V) are "all wheel drive all the time," but I know this means that only two wheels actually drive the vehicle until some slippage is detected and torque is transferred. I am hoping that the 4Runner is still a true 4WD vehicle, meaning that all four wheels are always engaged and driving the vehicle. Is my hope correct? Thanks in advance for any help.
  • tlcmantlcman Posts: 220
    correct, there is a center differential that you can lock, spliting power 50/50 but otherwise under normal driving yes all wheels are powered equaly.
  • Any of you 4Runner aficionado's know the crawl ratio of a 2003 V6 4Runner 4WD...thanks

     

    Crawl ratio = rear end gear ratio X lowspeed transfer case gear ratio X 1st gear tranny gear ratio.

     

    P.S. I've always favored Toy's & Chevy's for this reason...never got them stuck like I got my Fords stuck & stuck & stuck...you get the idea.
  • tlcmantlcman Posts: 220
    stats are on toyotas specs sheet under 4Runner vehicle here

     

    http://www.toyota.com

     

    -Mike
  • wwestwwest Posts: 10,706
    Isn't the "new" 4runner's AWD system rear biased, 30/70 F/R, or does it go from 50/50 to 30/70 as lateral forces build (more need to dedicate front traction to directional control), as the literature seems to imply??

     

    And lifting the throttle for recovering from understear or plowing in a FWD vehicle does not always, or maybe even rarely, result in recovery.

     

    Cadillac actually installed an over-running clutch in their FWD vehicles with the high HP/Torque Northstar engine to help prevent loss of control resulting from your recommended recovery procedure.

     

    In many FWD vehicles lifting the throttle will oftentimes result in enough engine drag torque to the front wheels that when "added" to the lateral forces from stearing will still exceed the front tires' traction coefficient.

     

    I am extremely partial to vehicles that allocate the front tire contact patches to directional control and the rear to drive and drag.
  • tlcmantlcman Posts: 220
    which 4 Runner are you talking about V8 or V6

     

    and secondly

     

    when you want to accelerate and turn at the same time you put two forces on the tyre; directional changes, and acceleration. The combination of these and the ammount is what starts understeer, the tyres can not keep traction with the steering angle and the amount of torque that is being put to them. These two reasons are why the tyres break loose, so if you correct them, then you will correct the probblem, thats too simplistic but i could write a page on it if you would like.

     

    "over-running clutch"

     

    Im assuming this means that the changing of gears is mutch more smooth, this means that like the word implies, the clutch mechanism gives mroe slip so that there is less force applied to the front tyres right away which could cause them to break loose, and on a car not equiped witha over-running clutch you would correct that by lifting the throttle like I said.
  • wwestwwest Posts: 10,706
    Prevents the engine from being "driven" by the tires' roadbed traction. No engine braking, drag torque, fewer incidents of crashing due to loss of control on a curving downhill icy run.

     

    Get off the gas fully, front tire traction fully dedicated to maintaining directional control.
  • tlcmantlcman Posts: 220
    in the car equiped with that device yes you should but others without it, you would not want to jump out of the gas because you would put againa decel. force on the tyres. stay in the gas just with the right amount of foot and you will keep the tyres moving the speed of the ground. I've never driven a car with an over running clutch, so i can only go by what you say.
  • wwestwwest Posts: 10,706
    learning to feather the throttle, finding the sweet spot, such that the engine is neither driving nor dragging, is somehow easier to accomplish than learning to stear into the skid in a RWD vehicle?

     

    NOT!

     

    Just as the AAA is now suggesting for recovery from understearing FWD vehicles, slipping the transmission into neutral is somewhat cumbersome but will always work.
  • tlcmantlcman Posts: 220
    again that suport what I said... i dont think that you understood me. Understeer is easier to control, that also means that if you cant recover you can still have general control, oversteer if you cant regain control you can roll it or throw your pasenger or you into a light pole center divide, or what ever else might be aorund, Let up on the throttle slip it to and puting it in N is basicly the same you let the wheels keep their speed with the road, if you jump out of it and you car does not come with a ""overrunning clutch" then you are putting an engine break force on the tyres and defeating the purpous, N or less gas will work. Been driving for 35 years and half of my cars have been front wheel drive, born and raised in Colorado and have experianced my share of over and understeer, thank you. There is no sweet spot, infact its a pretty large area, You dont need a flight calculator by your side to calculate the throttle imput, All you need to do is not floor the throttle, or jump out of it, just let of a bit and decrease the steering angle, no calculators needed... Im sure you wanted to use one though.
  • pschreckpschreck Posts: 524
    Since when? AWD implies that the 4Runner doesn't have a two speed transfer case like a Subaru. The new 4Runner is Full-Time 4WD by my understanding.

     

    You guys need to get your terms straight or you're going to confuse people that are reading this forum for the first time and have little knowledge of these systems.
  • steverstever YooperlandPosts: 40,436
    Unfortunately even the manufacturers don't seem to be consistent with the terminology. I would hope that Toyota is consistent within its model lines though. Cliffy has a good summary in the first dozen posts or so.

     

    Steve, Host

    Moderator
    Need help navigating? stever@edmunds.com - or send a private message by clicking on my name.

  • wwestwwest Posts: 10,706
    Is simply an add-on to 4WD capability. Other than being a common "accessory" to many 4WD systems (and virtually ALL of the older ones), having a 2-speed transfer case does not relate in any way to AWD or 4WD.
  • pschreckpschreck Posts: 524
    Then what IS the difference between AWD and 4WD?

     

    I believe that a CENTER DIFFERENTIAL is an accessory to a 4WD system while a TRANSFER CASE is fundamental to a 4WD system.

     

    AWD never (that I know of) has a TRANSFER CASE.
  • wwestwwest Posts: 10,706
    except for marketing differentiation...

     

    AWD systems are presumed to be FULLTIME, but many 4WD systems were, and are, fulltime. I think the "marketeers" wanted to differentiate AWD for 4WD for good reason. AWD is generally taken to mean fulltime 4WD with no driver intervention.

     

    Most traditional 4WD systems, even those with fulltime mode, have other drive modes, thereby require driver intervention.

     

    The new 4runner, for instance, has a RWD mode, an AWD/4WD mode, and a part-time 4WD mode wherein the center differtial is locked.

     

    Disregarding its off-road capability entirely, the 4runner's fulltime system is likely one of the best in the market today.

     

    Oh, sorry, almost forgot. Most transfer cases also have a differential in the form of a planetary gear set. I think, not sure, the term "transfer case" has come to mean a 2 speed gearbox, by default.
  • Am putting together spec's for the '05 Tacoma we want to purchase(4WD, Auto., Off-Road #2, Impulse Pearl, Running Boards(RB), Bed Mat(CJ), JBL Stereo(EJ)...). Edmunds, and KBB list the below option:

     

    VEVSC w/DAC

    Includes Vehicle Stability Control (VSC) with Traction Control (TRAC), automatic limited slip differential, hill-start assist control (HAC) and downhill assist control (DAC). REQUIRES OG or PT or SJ or SN.

    But this is not listed as an option on the buyatoyota site. Does anyone have this option? Is this NOT an option with the vehicle I have described? I'll be doing in-town, occasional snow/ice, and some beach driving - is this package worth $800?
  • stove1stove1 Posts: 53
    It might help a little but I doubt it makes too much difference on snow and ice when you don't have traction. VSC operates by selective braking one of the wheels . What good that will do when you don't have traction on ice ?
  • hank14hank14 Posts: 133
    This thread and others like it should have a mandatory warning label that anyone who reads it should be prepared to become dazed and confused. If someone misuses their vehicle- from tire inflation to fluid type to how to use it's respective 4WD system, it's their own fault. Read your manual. Take a 4wd class. Practice in an empty parking lot, off road, or something. No wonder everyone is so confused. I only keep reading because it is comical. I think I'll stick to a Landcruiser specific forum from now on. Happy New Year.
  • wwestwwest Posts: 10,706
    The only time I can say for sure that my VSC kicked in was when I drove a bit too agressively through a water puddle as I turned left out of a driveway. Obviously the same thing could happen on a rain slicked street or even an oily spot.

     

    No ice or snow required.
  • This discussion thread is like reading a script for Abbott and Costello's Who's on First!

     

    B
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