Rain and "full-time AWD"

Yes, AWD will have better traction and will have a quicker reaction than just having 4wd. Most of the time you will not know it’s using all four wheels to drive unless it has a monitor to show you. The weather on the highways in Florida change instantly, you’ll be doing 70 and come upon rain puddles before you can react and than be on dry surface in 100 yards. So, yes AWD is better for that type of situation and icy patches on roads.

 

Anyone know what the power distribution is on the limited 4Runner? My 2021 Outback was 60% front 40 rear%. More to the rear, up ro 50% if slippage was detected.

 

It’s typically 40/60 front/rear.

 

Thank you.

 

I don't know of the variable power distribution in H4F mode. But I definitely know that when I'm in H4L its constant 50:50 split regardless slip or not or foot on gas or not. Unlike viscous clutch base system on a Subi where its upto 60% front 40 rear% when slip detected and give gas.

 

I’m not sure that’s true. I used to think it was, because I thought that front and rear driveshafts spinning at the same speed meant that they were delivering the same torque. But it doesn’t.

Have a look at including the links. I think that beacause of the way the Limited’s Torsen center diff is constructed, when it’s locked it’s delivering a constant 40/60 split.

 

It's a geared limited slip when unlocked which gives you 40/60 and 50/50 split when locked. Part time 4wd in 4wd or a locked center diff is always 50/50.

 

But what about when it’s not locked. I’ve always wondered about this and even the dealership has no idea.

 

My 4Runner is an ORP so I don't have AWD (just 4WD), but my LC200 is full-time with a center locker. The difference I've noticed is when you are on an incline and it's wet/snow, it makes a big difference in the ability to take off.

I got stuck in a friend's muddy yard, and locking the center diff made a pretty surprising difference.

However, without it locked, I can turn on pavement in 4HI/4LO without binding. One unexpected result of 4HI / 4LO with center unlocked is that while in 4WD I can make switchbacks on trails that my friends in their 4Runners had to 2 or 3 point turn. That was before I used turn assist, which is kinda meh, cause it could tear up the trail and rarely is it really needed.

 

My understanding is far from crystal clear on this. But I’m trying …

Can you explain please, if in an unloaded state, i.e. the vehicle is driving in a straight line and all 4 wheels have traction, and so within the differential the sun and epicycle gears are spinning at the same speed and the planet gears are stationary, and in this unloaded state the torque split is f/r 40/60 - how then does engaging the differential lock, which freezes the differential innards in their unloaded state, change the torque split from 40/60 to 50/50?

Here’s a nice reference.

 

The 40/60 split only happens when there's slip. There's an internal physical lock either by a clutch, locking collar or pin that doesn't allow for the differential action just like in a differential locker. I'm not sure what Toyota uses for the actual lock mechanism.

You can see a locking sleeve in this VW unit. http://chris.chemidl.in/wp-content/uploads/2015/01/24.jpg

 

@whippersnapper02,

I mean, I get what you’re saying. One way to think about it is that if you lock the center diff then the system mimics a part time 4WD transfer case. Which seems intuitive but may not be true.

And even if it were, the part time 4WD t-case distributes torque equally fore and aft, but it isn’t 50/50. It’s 100/100. No? I mean, if (with part time 4WD) there’s no traction at the front axle, and only traction at one wheel on the rear axle, and the rear diff lock is engaged, isn’t that 1 wheel getting 100% of the available torque?

 

Even a part time case is considered a 50/50 split. That 50/50 is still 100% to the ground spread to both axles. Then there's another 50/50 split at each diff making for 25% at each wheel but still 100 to the ground. There's a engineering explanation to all of it which I don't know. You wouldn't get 100% to the ground to one wheel since the other wheels are still engaged. There's torque vectoring systems in some AWD vehicles that can send more power to a single wheel by applying brakes or using clutches and because nothing is locked together and power can flow to one wheel.

 

Funny timing for this to pop up. We added a post today that about it.

https://aguyagirlandatrail.com/2022/12/07/winter-driving-with-4wd/

 

Nice write-up! Beautiful photos.

To avoid confusion, I prefer to differentiate AWD systems from 4WD systems, and to differentiate 4WD systems into part-time 4WD and full-time 4WD. Let me explain:

In your blog post you state “An All Wheel Drive system has a front, center, and rear differential. This allows AWD vehicles to have each wheel rotating at different speeds while still being driven and applying power.” There are plenty of AWD systems without a center differential. Volvo, Volkswagen and others use a Haldex rear end to engage the rear end as required. There are other similar systems used by various other auto makers. Subaru’s so-called center differential uses a vicious coupling rather than a conventional geared differential. These AWD systems certainly have their place. Conveniently they work with no user input, receiving their instructions from a computer. Mode selection adjusts the behavior of the computer control to suit various types of terrain. This makes the systems much more idiot-proof. But the main characteristic that all these systems share is that they are reactive. Mostly they engage only after wheel spin has occurred, and after precious momentum has been lost.

Part-time and full-time 4WD systems are proactive. They are superior in terms of off-road performance, with the deficit that they require more knowledge on the part of the driver.

The Limited’s full-time system, with a locking center differential, provides the most convenience and capability. Only vehicles with three locking differentials are more capable.

All the usual caveats apply - IMHO, YMMV, etc.

 

That’s also why I put the disclaimer “**That is a generalization about AWD, there are a ton of variations out there**” in there. There’s some AWD hybrids that are gas powered fwd and electric rwd. The point is the same without diving into 100 different iterations or AWD.

 

I'd say that vehicles with two locking differentials are more capable, also. But, not necessarily as good for street driving in slick conditions.

 

No snow and never off road: AWD has very little advantage except on high performance cars where it helps to maximize acceleration. I think when combined with modern stability control systems it might have some small safety advantage in the rain, but again it would be small. What does make a big difference, in any condition, is TIRES.

I’m very happy to have AWD/full-time 4WD in my Limited, but only because of the number of times each year I find myself driving in mixed conditions where it’s dry one moment, wet the next, and snowy or icy the moment after that. All on the same road or trip. Part time 4WD is a PITA in that situation, so you often don’t have it engaged when you need it. And FWD or RWD is certainly less safe and capable.

 

I was under the impression that a full time 4wd system was different than "AWD".

Doesn't the full time 4wd setup distribute the power 50/50 to the front and rear? Does anyone here actually know this?

I would think that if anyone actually needs 4wd in the rain, they either need better tires, or they need to ease off the throttle.

 

2wd vs full time 4wd = Advantage full time 4wd
4wd vs center diff lock = Same
4wd low range vs 4LL = Same
4wd H or L with 1 diff lock vs L or H center diff lock = advantage 4wd with locker

 

Sure it is. But, I don't believe that AWD is the same as full time 4WD

It seems like some AWD vehicles use different methods for engaging the rear wheels (as opposed to a center differential) and sometimes put more power to the front axle.

 

Toyota uses a Torsen center diff. Power is 40/60 when there’s slip.

AWD and full time 4wd can be interchanged but AWD is usually refers to vehicles not equipped with a center diff lock.

 

I don’t think there’s a single gospel truth on this issue. But I consider “full time 4WD” to be AWD with the addition of a locking differential. The Limited is one of a very few vehicles to have this combination. No “AWD” cars (Subarus etc) have this.

Further up this thread I think it’s determined that the Limited is a default 60/40 when un locked and of course 50/50 when locked. The 60/40 automatically changes in response to slip, just as in AWD systems. Some change solely from mechanical forces, some with the aid of computers.

 

You are correct. There are tons of YouTube videos and articles on this, so I'm not going to get into it in crazy detail. But as somebody mentioned above, there are plenty of AWD vehicles that do not have any type of center differential, and have different electric clutch packs or viscous couplings to engage the rear wheels. I have an AWD Volvo, it does not have any center differential or transfer case.

Full-time 4WD would be something like a Land Cruiser, which has the ability to shift into low range and lock the center differential. Another such vehicle would be the 4R Limited, as well as the manual FJ cruisers, even some 1970s Chevy Blazers had full-time 4WD.

Even the Jeep NP242 Selec-Trac transfer case had a full-time 4WD mode, those were used from the '80s into the mid-2000s, and I think they use a version of it now in the Wrangler.

Also, a lot of AWD cars are FWD 90% of the time, and only engage the rear wheels when slip is detected in the front. This is how my Volvo works. There's an electric fault right now, my rear wheels are not engaging. I can mash the gas and literally smoke the front tires. In a part-time, or traditional full-time 4WD, an electric fault is not going to prevent your wheels from engaging, since it's a mechanical connection.

AWD means that there is the ABILITY to send power to all wheels, but not necessarily all the time.

Full-time for WD means just that, it's in 4WD all of the time. Whether you shift into low range, and or lock, the center differential, is up to you. Also, there are fulltime 4WD vehicles that don't have a lockable center differential, I believe the early Sequoia models you couldn't lock the center diff, as well as certain years of the Land Rover Discos.

And IMO, the advantage of the center differential is that it allows for the full-time 4WD to be operated on the street. Once you lock the center differential, it acts no different than the part-time case in the TRD OR, SR5, or Pro model 4Runners.

 

I'll say as an owner of 2 4Runner ORPs that I loved my first, and still love my second. However, the one handy part of AWD/FT4WD (Limited 4R and LC) is you don't have to decide when to use it. For me, not a big deal, but when the wife or someone borrows the car, it just drives. In fact, it's rather odd experience that I don't have too much to think about for daily, just drive it.

Bonus: Pulling trailer in rain/snow up hills sure is nice with 4WD. But, I'll second the person who said tires matter the most. 200% agree

 

This range of opinions is why I say there's no single gospel truth on the matter. But to me, it's the presence of a locking differential that turns an AWD system into a Full Time 4WD system. The ability to lock a differential to force equal torque to both axles, regardless of conditions on the ground, is the most salient feature of 4WD. A system becomes "Full Time" 4WD when it has both that and the ability to send varying amounts of torque back and forth between the axles without having to lock the differential.

The presence of a low gear just makes a 4WD or AWD system more capable than it would be without it. It is not a defining feature of either system.

So actually I've changed my own mind. That is the gospel on this topic. I Have Spoken, It Is Written

 

I just thought this was funny!

The full time system definitely rules in snowy climates. My '03 had it, and it was excellent in snow!

 

I have to agree with what @Trail Runnah and @Singleminded have said.

If there weren't any difference, manufacturers wouldn't specify them as different features.

I don't believe they should be considered the same thing, because there seem to be some consistent differences.

 

I like the full time 4wd of the limiteds. Kinda disappointed when I found out you couldnt get it on OR versions. But as time passes, I like the simplicity of the part time system

Do limiteds have a rear locker option?

 

I wish Toyota would bring back "multi mode.". This was probably the coolest 4wd option they ever offered.

No locker option on the Limited.