question about part-time 4WD on Trail Edition
- Thread starter Fareastplaza
- Start date
Thai
Elite Member
But remember, ATRAC only works on the SAME axle. It does not coordinate b/w the axles. For example, if your whole front axle is deep in mud/snow/ice...you will be stuck if you did not lock the center diff. Why? ATRAC on the front axle will NOT operate because as far as it is concerned, the two front tires are spinning at the same speed (= no speed differences b/w wheels on the same axle)...thus, ATRAC will not intervene to brake any wheels on that front axle...thus, both tires on the front axle will spin freely like nothing has happened. This would mean ZERO traction on the front axle in the Torsen center diff eyes. So, it will send all torque to the front axle...and zero to the rear axle. You are screwed at this point...unless you can lock the center diff. But, locking the center diff is not instantaneous in most cases...so, you have to battle that issue as you try to get the center diff to engage. And since you have not locked the center diff yet and now are turning the wheels left and right to get unstuck, VSC will now intervene and shut down your engine because it thinks that you're sliding on the highway! Big problem...time to call the tow truck or a local Jeep to pull you out while being film for Youtube by the Jeep owner!
Thus, IMO, when you're off-roading, you should almost ALWAYS lock the center diff as you enter the trail. Make sure that it is there when you need it, instead of relying on lady luck to get it to engage AFTER you are stuck. In addition, locking the center diff will disable VSC, thus, you won't have a problem with the engine being dethrottled when you need more power.
In my Mercedes, i always lock the center diff upon entering a trail. And in most cases, i lock the rear diff also. In off-roading, you don't want to leave anything up to chance.
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But remember, ATRAC only works on the SAME axle. It does not coordinate b/w the axles. For example, if your whole front axle is deep in mud/snow/ice...you will be stuck if you did not lock the center diff. Why? ATRAC on the front axle will NOT operate because as far as it is concerned, the two front tires are spinning at the same speed (= no speed differences b/w wheels on the same axle)...thus, ATRAC will not intervene to brake any wheels on that front axle...thus, both tires on the front axle will spin freely like nothing has happened. This would mean ZERO traction on the front axle in the Torsen center diff eyes. So, it will send all torque to the front axle...and zero to the rear axle. You are screwed at this point...unless you can lock the center diff. But, locking the center diff is not instantaneous in most cases...so, you have to battle that issue as you try to get the center diff to engage. And since you have not locked the center diff yet and now are turning the wheels left and right to get unstuck, VSC will now intervene and shut down your engine because it thinks that you're sliding on the highway! Big problem...time to call the tow truck or a local Jeep to pull you out while being film for Youtube by the Jeep owner!
Thus, IMO, when you're off-roading, you should almost ALWAYS lock the center diff as you enter the trail. Make sure that it is there when you need it, instead of relying on lady luck to get it to engage AFTER you are stuck. In addition, locking the center diff will disable VSC, thus, you won't have a problem with the engine being dethrottled when you need more power.
In my Mercedes, i always lock the center diff upon entering a trail. And in most cases, i lock the rear diff also. In off-roading, you don't want to leave anything up to chance.
Yeah, I realize all that, but in order for ATRAC not to work, you'd have to have the same exact amount of traction on each of the wheels on an axle. The odds of that happening are virtually zero. In just about any situation, either the right side or left side wheel will have more or less traction than the other, enabling ATRAC to do it's thing. In a practical application, ATRAC would be braking the wheel with less traction, thus sending torque to the wheel with more traction. And while that's happening, the Torsen would be adjusting torque front & rear. But like you said, just lock it up if there's any doubt.
Thai
Elite Member
There must be enough speed differences b/w the wheels on the same axle for ATRAC to work...and then is there enough traction differences for the Torsen to send power to the rear? Again, you're leaving it up to lady luck to help you out...not a good thing to do in off-roading IMO.
I am not sure which 4runner you have DocMT, but the 4th gen ATRAC system is rather "easy going" and not very aggressive at slowing down a slipping wheel...in such cases, you need a lot of wheel speed differences and even then, it does not lock up the wheel aggressively. The A-TRAC that really works is found on the 2009 4runner Trail and the 5th gen 4runner (along with FJ Cruiser as an option).
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But remember, ATRAC only works on the SAME axle. It does not coordinate b/w the axles. For example, if your whole front axle is deep in mud/snow/ice...you will be stuck if you did not lock the center diff. Why? ATRAC on the front axle will NOT operate because as far as it is concerned, the two front tires are spinning at the same speed (= no speed differences b/w wheels on the same axle)...thus, ATRAC will not intervene to brake any wheels on that front axle...thus, both tires on the front axle will spin freely like nothing has happened. This would mean ZERO traction on the front axle in the Torsen center diff eyes. So, it will send all torque to the front axle...and zero to the rear axle. You are screwed at this point...unless you can lock the center diff. But, locking the center diff is not instantaneous in most cases...so, you have to battle that issue as you try to get the center diff to engage. And since you have not locked the center diff yet and now are turning the wheels left and right to get unstuck, VSC will now intervene and shut down your engine because it thinks that you're sliding on the highway! Big problem...time to call the tow truck or a local Jeep to pull you out while being film for Youtube by the Jeep owner!
Thus, IMO, when you're off-roading, you should almost ALWAYS lock the center diff as you enter the trail. Make sure that it is there when you need it, instead of relying on lady luck to get it to engage AFTER you are stuck. In addition, locking the center diff will disable VSC, thus, you won't have a problem with the engine being dethrottled when you need more power.
In my Mercedes, i always lock the center diff upon entering a trail. And in most cases, i lock the rear diff also. In off-roading, you don't want to leave anything up to chance.
You just solved the mystery of how I got stuck in my old 4runner with awd. I had not locked the center diff til I got stuck. At that point it made no difference, I wasn't going anywhere.
Thanks for the detailed explanation.
JL
I can only say that the ATRAC in my 4th gen really seems to be pretty aggressive. It doesn't take much before it kicks in. Still though, my comments weren't really based on offroading. This was more of a discussion of driving in snow (on the road), where you're much more likely to encounter some wheels with traction and others without traction. My 4Runner feels like a damn tank in the snow, complete with tracks instead of wheels. So I'm completely happy with the way the whole system works, right from the ATRAC to the center diff.
zepjet
New member
But remember, ATRAC only works on the SAME axle. It does not coordinate b/w the axles. For example, if your whole front axle is deep in mud/snow/ice...you will be stuck if you did not lock the center diff. Why? ATRAC on the front axle will NOT operate because as far as it is concerned, the two front tires are spinning at the same speed (= no speed differences b/w wheels on the same axle)...thus, ATRAC will not intervene to brake any wheels on that front axle...thus, both tires on the front axle will spin freely like nothing has happened. This would mean ZERO traction on the front axle in the Torsen center diff eyes. So, it will send all torque to the front axle...and zero to the rear axle. You are screwed at this point...unless you can lock the center diff. But, locking the center diff is not instantaneous in most cases...so, you have to battle that issue as you try to get the center diff to engage. And since you have not locked the center diff yet and now are turning the wheels left and right to get unstuck, VSC will now intervene and shut down your engine because it thinks that you're sliding on the highway! Big problem...time to call the tow truck or a local Jeep to pull you out while being film for Youtube by the Jeep owner!
Thus, IMO, when you're off-roading, you should almost ALWAYS lock the center diff as you enter the trail. Make sure that it is there when you need it, instead of relying on lady luck to get it to engage AFTER you are stuck. In addition, locking the center diff will disable VSC, thus, you won't have a problem with the engine being dethrottled when you need more power.
In my Mercedes, i always lock the center diff upon entering a trail. And in most cases, i lock the rear diff also. In off-roading, you don't want to leave anything up to chance.
Since ATRAC only works in 4LO with the center diff locked, it's sort of a moot point isn't it?
Also, are you sure that ATRAC only works on the same axle? I would've guessed that the ECU would monitor slippage on all four wheels and modulate accordingly. But just a guess.
On the 4th gen 4Runner ATRAC works in 4HI or 4LO and with or without the center diff locked.
And ATRAC is what controls torque delivery side-to-side. If the front left wheel spins, ATRAC brakes that wheel, which sends torque to the front right wheel. Same is true for the rear axle. The center diff controls torque delivery front and rear. When you lock the center diff, you're making 50% of the torque go to the front axle and the other 50% to the rear axle. Put it all together and you have torque being sent to both the front and rear (via a locked center diff) and from side-to-side via ATRAC. It's a great system.
Fareastplaza
New member
I am surprised so many replies here. I am really appriciate all your guys help. Some answer/discussing seems beyond my knowledge. Anway, can anybody tell me how Trail Edition to be operated when facing mixed surface and tunning? Should I keep switch between RWD and 4WD? Can I do this when I am driving? Is there any difference when my speed hits 80miles and 40miles?
zepjet
New member
Gotcha, thanks. Yeah, I'm well aware of how differentials work.
Interestingly enough, a good video of ATRAC in use... YouTube - CM2010 151.MOV
Your owner's manual will explain that the part-time transfer case on the Trail should not be operated on dry pavement. That's because it will bind around turns and potentially cause damage to the transfer case. If you wanted the ability to keep the vehicle in 4wd and not worry about the road surface, you need to buy the Limited version because it has a center differential and will not be negatively affected by driving on any road surfaces, even if it's completely dry.
If I were you, I'd use 4wd only when you really need it...for example if there's snow on the road or if you're driving in dirt or other "loose" surfaces like rock/gravel etc..
trentfysty
New member
Having driven an AWD Land Rover Discovery I thought I would chime in on the center locking vs. rear locking debate here. First of all to the original poster, you can't drive a pt 4wd on dry pavement while in 4wd for any length of time without risking damage to the system.
Now to chime in on the debate. AWD is a no-brainer system when it comes to snow and ice. It is there when you need it without having to do anything. While it does make it easy not having to shift into 4wd I don't think that it provides better traction. Compared to other 2wd vehicles my Land Rover's AWD hasn't been noticeably better unless in deep snow. With that said a pt 4wd system would be just a capable in deep snow with no worries of harming the system.
Thai explained the benefits of a center locking diff very well. I can't say that I automatically locked my center diff when going off road in the Disco unless I was going into an obviously risky area such as mud. I also used the rear locker on occasion usually after loosing traction. My Disco did not have all of the traction control etc that the 4runner does but I never had any issue that the locking center diff or rear locker couldn't overcome that would have been able to be overcome by ATRAC etc. Mostly very deep snow causing high centering is what got me stuck but that is why you have winch right?
I don't see AWD as that much superior to pt 4wd as say ABS to non-abs. There is no way I can pump the breaks as fast as ABS so clearly it provides a service that I could not otherwise achieve. Pt 4wd is available when needed but does require one to consciously think about engaging it. Granted, AWD does provide a peace of mind that it is always there when needed without having to engage it. That could help to avoid an accident. I don't think that AWD with a torsen diff provides any better traction then a pt 4wd system when in 4wd. The ability to shift torque to the front or rear axels vs. being locked will make a very little if any difference. What I feel it comes down to mostly is ease of use and the remote possibility that having the system always engaged would allow you to avoid a loss of traction that you couldn't avoid by having to shift the system into 4wd.
I do find it odd that Toyota took a step back in that regard but it clearly goes to cost. Also, is there any real difference in actual gas mileage between a TE/SR5 in 2wd vs. a LE that is AWD? If there is that could be one more reason that Toyota chose to revert to PT 4wd was to up the overall gas mileage of the 4runner. Also, is there any information out there that compares the maintenance costs of AWD vs. PT 4wd? That would be interesting to see if one costs less to maintain over time.
Now to chime in on the debate. AWD is a no-brainer system when it comes to snow and ice. It is there when you need it without having to do anything. While it does make it easy not having to shift into 4wd I don't think that it provides better traction. Compared to other 2wd vehicles my Land Rover's AWD hasn't been noticeably better unless in deep snow. With that said a pt 4wd system would be just a capable in deep snow with no worries of harming the system.
Thai explained the benefits of a center locking diff very well. I can't say that I automatically locked my center diff when going off road in the Disco unless I was going into an obviously risky area such as mud. I also used the rear locker on occasion usually after loosing traction. My Disco did not have all of the traction control etc that the 4runner does but I never had any issue that the locking center diff or rear locker couldn't overcome that would have been able to be overcome by ATRAC etc. Mostly very deep snow causing high centering is what got me stuck but that is why you have winch right?
I don't see AWD as that much superior to pt 4wd as say ABS to non-abs. There is no way I can pump the breaks as fast as ABS so clearly it provides a service that I could not otherwise achieve. Pt 4wd is available when needed but does require one to consciously think about engaging it. Granted, AWD does provide a peace of mind that it is always there when needed without having to engage it. That could help to avoid an accident. I don't think that AWD with a torsen diff provides any better traction then a pt 4wd system when in 4wd. The ability to shift torque to the front or rear axels vs. being locked will make a very little if any difference. What I feel it comes down to mostly is ease of use and the remote possibility that having the system always engaged would allow you to avoid a loss of traction that you couldn't avoid by having to shift the system into 4wd.
I do find it odd that Toyota took a step back in that regard but it clearly goes to cost. Also, is there any real difference in actual gas mileage between a TE/SR5 in 2wd vs. a LE that is AWD? If there is that could be one more reason that Toyota chose to revert to PT 4wd was to up the overall gas mileage of the 4runner. Also, is there any information out there that compares the maintenance costs of AWD vs. PT 4wd? That would be interesting to see if one costs less to maintain over time.
Thai
Elite Member
My opinion is that you keep it 2wd and let VSC and TRAC (controlling slippage on your rear axle) do their job.
I don't know if there's a real world difference, but I do know that the fuel economy rating for both is 17 city/22 highway.
trentfysty
New member
I've heard people make the claim that pt 4wd is better because of the gas mileage but never actually seen it documented by the EPA mileage crap. I think it would be hard to prove a real world difference due to different driving conditions, weight in vehicle, gas, tires etc. Maybe it's one for Myth Busters?
It would be very difficult to prove because of all the variables. The fact that the EPA rating is the same for two equivalent vehicles (with one being P/T and the other F/T 4wd) is enough to convince me that there isn't a real world difference in fuel economy.
trentfysty
New member
I agree. The major reason has to be cost. I do think that people would be willing to pay and extra $2k or so to have the AWD in the TE. It will probably come in the mid model cycle refresh.
scanny
Senior Member
I see that discussion went way too techical, so just an example.
I was driving a highway when it started snowing. At first I was with traffic at about 120km/h (2wd). First falling snow was melting then it started accumulating, traffic slowed down to 100 km/h. At this poing I start thinking about turning on 4x4, but it's can be done under 80 km/h. So I waited to turn on 4x4 when traffic is slow enough. And then I drove in 4x4, passed snow, road became wet, then mix wet and dry, then solid dry and I turned 4x4 off. I should say that TRAC and VSC is pretty good in 2wd mode, I don't think I needed 4x4 that bad in this case but the truck is way more stable in 4x4 mode.
Further on the subject I must confess that on few occasions I turned from unplowed residential street to dry main street in 4x4 - well I felt guilty about it, but didn't notice any tightness, binding or other negitive things. People say that you will experience buinding when you park or do a U-turn or do other tight turns on dry pavement, I wouldn't do that.
My guess is that we'll never see it in the 5th gen Trail Edition. It's already available in the Limited, so Toyota is giving the option for someone who REALLY wants fulltime 4wd and is willing to pay extra for it.
Koz
New member
Here is the simple difference; The LE with full time 4WD has a Torsen locking center diff which incorporates limited slip. On dry pavement the diff (not locked) will provide a 40F/60R torque split. As soon as a loss of traction occurs torque is transferred to front or rear axle that has traction. It can move up to 47% of the torque to the front and up to 71% to the rear.
The part time 4WD in the SR5/TE simple has either 100% to the rear or a 50/50 split. The TE also has a rear locker that locks the rear wheels like there is a solid axle between the rear wheels. This really helps when one of the rear wheels has traction. The ATRAC can only pulse the brake on the wheel with no traction to divert a small percentage of torque to the wheel with traction (nothing like the locker's 50/50 split). The rear locker is not very useful in wet or snow conditions.
If your main driving conditions consist of on-road with bad weather get the LIMITED!
Koz
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