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4WD and AWD systems explained

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Comments

  • guidrypguidryp Member Posts: 7
    Again what conditions? Front LSD is pretty rare in general consumer vehicles. Its a little more complicated and maybe not the best idea in the snow, since you could lose lateral stability with both fronts spinning.

    Then again I think a rear LSD is overkill on a road going vehicle. I once tried my miata in a fresh 1 Inch snowfall and with the rear LSD engaging the back end was essentially floating free. Granted they were summer tires, but if only one rear was spinning, I would have had more lateral stability.

    Traction control systems don't increase spinning so they may be a better solution for a road vehicle. They usually work on all driven wheels.
  • dohc32vdohc32v Member Posts: 60
    As I recall the flap over the Ford Explorer and Firestone tires was, the loss of vehicle control usually occured when one of the rear tires failed. The question I have is, was it more predominate on any a particular model of Explorer with certain options, like 4W drive, or AWD, or 2 WD, or two door verse 4 door. I don't think I have ever seen anything in print about that issue. I'm curious because I have an AWD V-8 Explorer. I love the AWD feature and wonder if that would provide more or less vehicle control with a front or rear tire failure. I have experienced blow-outs before in passengers cars (all RWD), a couple at fairly high speed, and never experienced a problem with vehicle control. I'm wondering now about AWD, as the vehicle certainly has different dynamics than say a RWD or FWD passenger car.
  • paisanpaisan Member Posts: 21,181
    The whole explorer problem was that it rolled if you put the pressure up too high. So they set the pressures lower which in turn heated up the tires. I'd rather have higher pressure and risk ther rollover than lower pressure and have a blowout.

    -mike
  • tlaurotlauro Member Posts: 504
    the A4WD in the Trailblazer is lightening quick though...your post makes it seem as if you'll fishtail into a ditch first...that's not the case, I don't have the millisecond specs, but I've tried to fishtail it and it won't in A4WD...it kicks in instantly.

    Also, how is TOD different? From what I've seen by Isuzu it's essentially the same as the Trailblazer and other Triplets A4WD.
  • paisanpaisan Member Posts: 21,181
    The TOD system put 15% power to the front as a std. so you essentially have power to both axles at all times. In addition ituses weight sensors to sense when there is additional weight on an axle, signaling more traction and shifting more power to that axle when needed. The TOD unit is built by Borg and Warner and is not the same unit used in the Envoy/Trailblazer. Also it is adpative so that it learns which situations (or what happens just before) it needs to shift power and in future manuvers that are similar it pre-emtively shifts the power to that axle.

    -mike
  • tlaurotlauro Member Posts: 504
    you did a better job than Isuzu at showing the system. nice stuff.

    I never looked at it as the style just isn't for me. I've also heard they lean and bend in turns more than most making it less fun and what not. Not sure if that's changed in 01-02. Plus, I love the I-6 in the Trailblazer. It's a blast and with some simple mods, I no longer miss my sport sedan.

    tim
  • paisanpaisan Member Posts: 21,181
    The Trooper is discoed due to poor sales after the 02 model year and the new isuzu Ascendor is going to be a Trailblazer XL. My only hope is that they use the TOD unit in the upcoming XL version of the Ascendor and Trailblazer.

    -mike
  • ateixeiraateixeira Member Posts: 72,587
    That might actually yield a fine end-product.

    -juice
  • paisanpaisan Member Posts: 21,181
    Still going to be built in Ohio by GM, no way it can match the reliability of the current trooper. But what can you do? GM owns 49% of Isuzu. :(

    -mike
  • ateixeiraateixeira Member Posts: 72,587
    Why stop production on the 2nd most durable SUV in the mid-size class (per JD Power)? Seems absolutely stupid to me.

    At least let Isuzu assemble it in the same place, given the solid track record for build quality.

    -juice
  • tlaurotlauro Member Posts: 504
    just a jab....all in good fun.

    "most durable SUV "

    you may want to check out how a 5mph parkinglot accident would affect the almighty Isuzu's. let's hope it takes to off road use okay as the grocery store and malls will cost you some money.

    Check out the costs on the others too! WOW!!!
    http://www.hwysafety.org/vehicle_ratings/low_speed_midsuv.htm
  • spdmtr5spdmtr5 Member Posts: 111
    Tires,tires,tires.No tread-no go.Snow deeper than ground clearence-no go.Have a Dodge 4x4 its been stuck.Just bought the wife a trailblazer-AWESOME! I hear dual exhaust nets another 30hp.
  • ateixeiraateixeira Member Posts: 72,587
    I've seen those bumper tests. But you haven't seen the rhino bars on paisan's Troopa. ;-)

    He has a hitch mounted rear bumper thingy, too. Pretty wild.

    30hp from an exhaust by itself? Sounds optimistic. Maybe if you get headers, new cat, mid pipes and mufflers.

    -juice
  • spdmtr5spdmtr5 Member Posts: 111
    There is a huge resonater muffler at the rear.Without it rear clearence would be much better-maybe sound better-maybe more hp.
  • paisanpaisan Member Posts: 21,181
    Anyone who backs into a pole deserves any damage they receive, they shouldn't drive a big vehicle if they can't handle it. If you are rear ended (and I know at least 5 Trooper owners who have been) you are not likely to sustain nearly as much damage. My buddy was rear ended by a lexus LS400 @ 30mph (he was barely rolling) and he took on 4k damage, the LS400 was totalled.

    Yeah and that Trailbazer has the worst angles of approach and departure. Why would you need a dual exhaust anyway? Are you drag racing your trailblazer, cause most sedans will outrace the trailblazer.

    The Trooper won 2nd place in the JD Power & Associates Mid-size SUV reliability award right behind the Toyota 4-runner. I don't think any American SUV has come close to that recently.

    -mike
  • tlaurotlauro Member Posts: 504
    Actually 30hp is pretty realistic according to Ted Robertson the lead designer. They actually achieved this with the stock header pipe and a high performance 3" exhuast. The split into duals was more for appearance according to his email to me.

    I'm building mine to have just one pipe out the rear of the vehicle similar in appearance to the Toyota Sequoia Setup. Of course dropping the resonator will be needed and adding a quite flow flowmaster in place of the stock muffler will be needed for me to do this and still maintain a quiet(er) truck.

    I'm not actively racing my TB at the track like my GTP, but I have and will take it. Bone Stock it ran 15.675 in the 1/4. Eventually I'll have it below 15. Even in today's world though, 15.6's aren't bad for a performance sedan let alone a 4500lb SUV.

    tim
  • spdmtr5spdmtr5 Member Posts: 111
    Not a racer-would like to have sea level power here in Colo.Wonder if K&N has any kits yet?Going to Laughlin Nev. over the holidays-400 ft.then I should see 0-60 in 8 seconds!
  • paisanpaisan Member Posts: 21,181
    Don't worry there will likely be a few SCs out for the I6 in a few months I'm sure. The GM aftermarket is very strong so I'm confident it'll be out shortly.

    -mike
  • spdmtr5spdmtr5 Member Posts: 111
    Mike,keep us posted on your mods.If anyone wants info on Colo.4x4 passes,I have been over most of them.Thanks,Fred
  • hengheng Member Posts: 411
    I was at the dealer having the encoder replaced on my 2000 Jimmy and was looking at the Envoys some of which had locking rear diffs.

    Anyone know the details on Envoy locking rear diffs? How are they actuated?
  • lakesuperiorlakesuperior Member Posts: 1
    I want (don't necessarily need right now) a new vehicle to replace a Jeep Cherokee and a VW Passat. I hate the handling of the Jeep and how quickly it rusted. But, I can really bust through snow & mud with it. I love the VW, but be realistic even with excellent Pirelli's I can't take it where I need to at times. I don't know - AWD, 4WD, and the variations thereof...

    I live in the middle of "nowhere" - a place that can literally receive many feet of snow overnight. I work in EMS and Rescue Services, so I must have something that can maneuver at speed during the nice days (plus I enjoy driving - feeling the road), and take on the depth of snow during those "other" days. It also has to carry all of my gear, too, and a dog that's with me all of the time - the Passat is a tight squeeze & we need more room.

    I'm trapped between wanting a car or a SUV - something that hugs corners versus sloshes all over the place never feeling the road through the wheel.

    I've contemplated squeezing into an A4Quattro, a VW 4Motion, a wagon (I'm not sure if I'm ready to be seen in a wagon - ha!) of either brand that would allow me to keep the furrball in the back, or a Trailblazer (I know that doesn't even belong in the same category - but they don't look too bad, and dealers are everywhere). I recently ruled out the 4Motion sedan that handled because the back seats don't fold down, unlike the Audi! Must be able to carry backboards (spineboards). I've looked at the entire Subaru line-up (I better - I'm affiliated with rallies) but I very much dislike the looks, and the interior's are a little too cheap feeling and when you close the door....where's the nice, quality thud sound?

    Help - Suggestions? Others to look at? Should I keep saving my sheckles to buy something that will truly fit my needs that's more than 30K? What should I sacrifice on, if nothing is going to fit the bill?
  • paisanpaisan Member Posts: 21,181
    Get a Trooper S with TOD. Add to that about $500 in top quality AT tires, and $500 in springs/shocks and you will have a speedy AWD vehicle that will suit your needs well. They have excellent reliability (2nd behind pathfinder in JD Powers and Consumer Reports) and the TOD system is great in the deepest of snow (used mine in the adirondacks in 2+ feet of heavy snow w/o a problem) Just something to look into.

    -mike
  • ateixeiraateixeira Member Posts: 72,587
    The problem with the VeeDub is ground clearance. You only get something like 4" or so. Same with the Audi A4, which is smaller anyway.

    Subaru's sedans do not have seats that fold, either. They do have 6-8" of ground clearance, so too bad. The frameless doors mean the glass rattles when you slam the doors, but don't mistake that for a less-than-solid structure. Crash test results have been great.

    Other wagons with good ground clearance? Volvo XC, but that's only a wagon. Audi allroad quattro, also only a wagon, no sedan.

    S60 is supposed to get AWD soon, and the baby Jag will have it standard. BMW offers it, so choices are getting more abundant, but I doubt any of these will have the ground clearance you want.

    So you may need to look at SUVs.

    -juice
  • leomortleomort Member Posts: 453
    how does the Toyota 4Runner match up against the Trooper? In your opinion who has the better 4WD system?

    Leo
  • paisanpaisan Member Posts: 21,181
    Up until recently the 4-runner had a part-time 4wd system which is sub-par to any Dry-engagable/fulltime system. I believe they now have a system that can be activated on dry pavement but is locked at 50/50 torque split. The TOD system on the Isuzu IMHO is better than a 50/50 split cause it will shift around power and when you are stuck in a rut you just push the pedal and it will fluctuate power from f/r split of 0/100 to 50/50. This will allow your front wheels to grip (when 0 torque going to the front) and then it slowly applies power from 0->50% to the front axle which essentially acts like slipping in the clut to maintain traction. I've found that in snow the TOD system works better than if I leave it in 4wd Lo (which locks it at 50/50 torque split) Both systems are excellent though. The Trooper IMHO is a better deal cause it is ranked right below the 4-runner in JD power and Associates reliability ratings as well as Consumer Reports reliability ratings. Has far more room, and slightly more luxury than the 4-runner and sells for 5-10K less than a 4-runner. Current pricing on fully loaded Trooper LSs w/everything except leather is around $25.5K

    -mike
  • jmh62jmh62 Member Posts: 5
    Help!

    What system does the Acura MDX employ? How does it stack up against competition?

    I got different answers from different dealers and I want the truth!

    Help!
  • paisanpaisan Member Posts: 21,181
    It's essentially a FWD system, then it kicks in the back after slippage in the front. It actually has 2 different differentials in the rear IIRC so it can better direct the power to each back wheel. I don't like it cause it cuts all power to the rear after 19mph, no low range, and the engine sits in a FWD position(transverse). The rear wheel power was kind of an "afterthought" not integrated.

    -mike
  • ateixeiraateixeira Member Posts: 72,587
    Acura calls it VTM-4, but it is indeed primarily FWD and employs AWD on a part-time basis only.

    Having said that it's more capability than most people need, even though I prefer the feel of full-time or even rear-biased systems.

    -juice
  • wwestwwest Member Posts: 10,706
    Yesterday my wife and I took our daughter and our three GRANDkids up to Snoqualmie Pass to play in the snow. Since there were seven of us I couldn't take the 2001 RX AWD so I borrowed the company's AWD Aerostar.

    Driving into the upper parking lot at the summit became a challenge, one after another I watched as vehicles had to give up the "climb", back down and turn around.

    A Dodge/Chrysler FWD minivan was first, almost made it but then lost traction and never regained it. Honda Odessey next, even less success. Toyota HL, couldn't tell the model, didn't even make it to mid-point. Aerostar not only did fine there but went all the way up to the third parking area.

    Our youngest grandson soon got too cold and my wife and I returned with him to the car. My curosity got the best of me so I cruised the lower parking area until a parking spot opened up within sight of the bottom of the first incline.

    Lots and lots of vehicles couldn't pull the incline, most of them recognizably FWD. Quite a few vehicles did make it but some that didn't were quite a surprise.

    An 01 or 02 (VSC badge) RX AWD. He was clearly having trouble on the incline but he wasn't going to give up easily. I finally got out of our car and walked over to help by pushing and of course this made him just a little peeved. He finally had to give up and back down the incline.

    It was clear that his rear wheels were "driving", but apparently not enough to be of any help. I thought that I could also hear the TRAC "thumping".

    But the real surprise of the day was a late model 4runner that couldn't pull the incline. That driver was REALLY peeved. He even put in "low" range before he finally gave up.

    Absolutely no one seemed to have any trouble (driving, walking is another story)within the snow and ice packed LEVEL parking areas.

    The incline:

    Maybe 5% or less, and about 25 yards, packed snow and ice with some gravel and sand. We arrived late in the day, around 2 PM, and I'm sure the incline had been sanded early that morning but by now there was clearly more slippery surface than otherwise.

    It was so slippery in the center that you couldn't walk on it without falling and I watched several kids slid down the center of the incline in their ski boots.

    Why did the Aerostar do so well, equipped with simple summer tires, over others that shouldn't have failed? I don't know enough to be really sure but I suspect it was the fact that the Aerostar is basically RWD, 30/70, and switches to 50/50 if the rear wheels begine to slip.

    But why didn't the 4runner make it? The driver was using a conservative approach, not gunning it like most would.

    I'm wondering if this new type of LSD, using the brakes for implementation, just isn't up to these types of challenges. The reports I keep hearing is if you aren't carrying enough forward momentum when you hit a slippery area then you dead in the (frozen) water.

    Is there anyone out there with this type of experience with the ML?
  • ateixeiraateixeira Member Posts: 72,587
    I would suspect tires are the culprit half the time, the driver the other half. What tires do you have on your van?

    -juice
  • paisanpaisan Member Posts: 21,181
    The 4-runner is pretty light for it's engine, and gearing. The Aerostar IIRC is a pretty hefty vehicle. I agree tires are a big factor too.

    -mike
  • wwestwwest Member Posts: 10,706
    I generally run the QUIETEST tires I can buy for all my vehicles and carry a good set of chains when it is appropreate. I think the Aerostar might have M+S, but to be sure I'll have to check.
  • ateixeiraateixeira Member Posts: 72,587
    With my Subie I hardly even realize the pavement is slippery until I come to a steep incline and see other cars fail to make it up. I always carry a bag of sand in the winter, but the funny thing is it's always to help other motorists. :-)

    -juice
  • hengheng Member Posts: 411
    I just bought a pair of cable chains to supplement my open diff Jimmy for emergency situations. If I had the bucks to spend I would have bought the diamond chains for front and back.

    Anyone have experience with chains on 4WD vehicles?
  • wwestwwest Member Posts: 10,706
    what do you want to know?

    Had an 85 Jeep Cherokee Limited, purchased in 87, and then a 92 Jeep Cherokee Limited, purchased in 92. 92 is now serving time on a cattle and wheat ranch in North central Montana. Had four tire chains on both of them numerous times. never off-road except times I needed to drive into the ditch or in the median to get around so many FWD stalled vehicles.

    Basically not much reason for only two tire chains on a 4WD vehicle.

    Bought a MY2000 RX300 AWD in late 99, upgraded to 2001 RX300 AWD for HID, VSC, and TRAC. Ignored the ML320 at the time becuase of its poor reliability record.

    Oh, actaul link chains never cable chains.
  • leomortleomort Member Posts: 453
    wow, I'm surprise to hear about the 4Runner. Toyota's prime off-road stomping 4x4.

    Leo
  • wwestwwest Member Posts: 10,706
    I don't think he saw the Aerostar succeed where he couldn't, luckily.
  • rob222rob222 Member Posts: 49
    Of course Buick's new entry has the Versatrak AWD system as an option. The only offroad use for our 93 Grand Cherokee Wagoneer is on the Outer Banks of NC where it has no problem cutting through the sand. I really am compelled by the flexibility and ride of the RDV, but having never seen a AWD minivan on the beach wonder if it could it. Only 1.3 inches less clearance then my GC at 6.9 inches. Most GM dealers want to sell me an Envoy.

    Any thoughts.
  • wwestwwest Member Posts: 10,706
    As a current owner of a T&C AWD I would not venture to try it. I bought AWD for unpredictable LTS events, not to go looking for (trouble) them.

    LTS: Low Traction Surface.
  • ateixeiraateixeira Member Posts: 72,587
    I believe the Rendezvous is primarily FWD, with the rear axle kicking in only part-time to assist. I test drove one and it basically felt like FWD. I'm not sure it is all well suited as a full time AWD system or a true 4WD system.

    -juice
  • ak4x4ak4x4 Member Posts: 126
    Justwant to get my imput on this. Alot of people do not understand the difference between AWD and 4wd. I currently own 01 Silverado 1500 ext cab 4x4(Yes it will apply smae frameas a Subarban) While Subarus are great cars here is prime example of misconseption. Subarus are great for on-road us and going fast with grip through the corners. This is the tradeoff point. While I have seen many AWD car and truck owners think they can go where 4x4 can this is not true by a longshot. If anyone remembers the Honda and Kia commercial from a few years back?? The couple in the Hondanever made it. They got stuck AWD is just like Subaru says it is "From the wheels that slip to the wheels that grip" People nee to understand that their AWD Lexus or any other small
    SUV/pickup cannot compete with a 4x4 no matter what size engine you have! Let's see the outback owner take the car 4bying. I gues this is a common misconception due to the fact people think they are the same. Heck the car companys don't give people enough info. My point is that people need to understand the difference between these two systems. Yes the C3 Sierra and Silverado are the same. But one can go 4buying while the other has freakish handeling....Just my thougths.
  • ak4x4ak4x4 Member Posts: 126
    Your Subie is a good car(What model do you own?) Almost bought a 01 WRX. What impresed me was the handeling. 80+mph on Mountain(Alaska)roads without a slip in wet weather. But how do you think your car would do(With studs) but no chains on a hill covered with ice that has not been sanded??? I can bearly make it up with my 300 hp engaged in 4wL and no I don't spin the tires. SUbies are great don't get me wrong, but up here in Alaska nature does prevail and in conditions like that do you think you would wind up getting pulled(Like I did to a 2.5 RS 2 days ago) when that happens?? And chains within Anchorage city limits are illegal. And it's not just your Subie, I am talking about all the AWD cars and trucks out their(Honda CRV's, Eclipse an Talon AWD's, 3000 GT's, Subies, etc... Tell me what u think...
  • wwestwwest Member Posts: 10,706
    Has the best, smoothest roads in the wintertime, water finds it own level and then freezes, perfectly smooth roads, no potholes.

    But in the spring, come thawing...
  • paisanpaisan Member Posts: 21,181
    The biggest problem with off-roading a subaru (and I off-road my Trooper often) is not the AWD system, but rather the overhangs (angle of approach especially) and the tires that come std on them. Throw a set or ATs or MTs on a Forester and approach obstacles correctly and you are golden on all but the hardest items. Oh yeah skid plates would help too, but skid plates aren't std on most SUVs sold in the US including full sized ones.

    -mike
  • ateixeiraateixeira Member Posts: 72,587
    Keep something in mind - the Forester is very light, mine is about 3100 lbs, and that can be an advantage in many scenarios. I drove by a big diesel GM pickup this year at the Outer Banks, who had sunk in with its narrow tires and high curb weight. He said in low gear the tires would just spin more easily. Driver error - he had not aired down (I did).

    I'm not saying I can go rock crawling, but then again I never wanted to. Not in my primary driver. I've seen the damage Jeeps suffer after off road trip, limping home. No thanks!

    The Kia commercial was a total set up. Watch it again - they carefully place the front tires in a dip full of sand, and the driver doesn't stay on the gas long enough to send any power at all to the rear wheels, he just pumps the gas and lets go. The video has been picked apart many times on the CR-V threads.

    Besides, Subaru's system is different in that the rear axle gets power all the time. All AWD systems are definitely not created equal.

    To answer your question, I am sure that with studs I would easily make it up that icy slope. Remember, I'm only carrying 3100 lbs.

    Mine has done well on soft sand, on dirt/grass at farms, and on unimproved roads at the Pine Barrens (mostly mud and sand). That's enough for me, I don't need any more capability.

    paisan is right, though, the achilles' heel is the angles of approach/departure, and to a lesser extent ground clearance. But you can get skid plates, taller springs, lift kits, and even angled bumpers to improve on that. Problem is, you give up what started as the best handling Sport/Cute.

    -juice
  • ak4x4ak4x4 Member Posts: 126
    What is the weight on a 2.5?? Just curious. Ad No not this hill. Everyone was sliding. Outbacks, Forresters, Chevys, Fords, Dodges. If a Ram 2500 deisel can't make it there's a problem. It was just to plain icy for any car tomake it up. We all wound up going into the plowed feild that had been covered with snow. Of course A big truck went first to leave deep tracks. I think the Subies like yours and the Outbacks are too low to do any off-roading. Yes they can do light duties. But I think the bulk of the Subies AWD comes in on Wet pavement. ANd on dry it does fantastic. That WRX would be fun to blast down a dirt road at 80mph though. That was the thought I got when I was driving it!!!.
  • jd150jd150 Member Posts: 13
    I just got the 2002 Explorer with the 3 push-buttons for 4WD Auto, 4WD High, and 4WD Low. I am trying to categorize this type of 4WD according to Drew's definition at the beginning of this thread. (Where he talks about permanent, full-time, part-time, 4WD, AWD, etc.) Where does this fall in? And,is this a good or best type of 4WD? Thanks. John
  • paisanpaisan Member Posts: 21,181
    Is that made by borg-warner? If it is the Borg-warner unit that the Trooper has it's a great system, applying 15% power to the front axle with up to 50/50 split, using weight and slip sensors. I'm not sure if they still use the borg-warner unit in the Fords though.

    -mike
  • paisanpaisan Member Posts: 21,181
    Check out http://isuzu-suvs.com/events for some off-road events we've run in NJ where the subies have come and conquered. Heck we had to have an old GL hatchback yank a Montero with 33s out of a rut! The subies will not do well rock-crawling, but not all off-road situations are rock-crawling.


    -mike

  • ateixeiraateixeira Member Posts: 72,587
    If it's frictionless ice, noone without studs would make it, I guess.

    We had some of that today. I was stuck behind cars that could not climb a 1/4 mile hill near my house until a truck laid down sand.

    The Foresters weigh 3100-3300 lbs, pretty light all things considered.

    -juice
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