Here is the description of the AWD system. It is a full time AWD system with a 50/50 torque split

Highlander AWD

Toyota uses VSC and TRAC control to distribute torque to individual wheels

Description of TRAC

Highlander TRAC


Description of VSC

Highlander VSC

So in summary the AWD system is simplistic with a 50/50 torque split and the torque to the wheels is computer contolled braking using VSC/TRAC

 

What do you think, summerwind, maybe add a sticky about the AWD systems and perhaps other systems associated with the Highlander? Seems like there's enough interest to justify it....

 

What do you think, summerwind, maybe add a sticky about the AWD systems and perhaps other systems associated with the Highlander? Seems like there's enough interest to justify it....

Sticky away:thumbsup:

 

Any other things like the key fob, security system, etc., that you or anyone else out there think would provide good systems information about the Highlander just shoot me a PM. :thumbsup:

 

What is the max torque it can send to rear wheel?

 

If this is true (i mean the AWD system as outlined in the document), then all differentials are OPEN differentials (including center diff). This means, if the two front wheels on the front axle lose traction completely (free spinning the same time), there will be no power (torque) transferred to rear axle. So the TC/VSC has to be smart enough to brake the two front wheels the same time to bring torque to rear axle. But we don't know that. This situation is not rare, going up a steep icy drive way is one case. I'd like to find out how TC/VSC works with this AWD system, anyone know?

I read some where that the HL has a viscous coupling center differential, which is a limited slip type, but it doesn't appear to be true. (http://stason.org/TULARC/vehicles/toyota-tundra/3-60-How-does-my-4x4-really-work-All.html)

 

then all differentials are OPEN differentials (including center diff). This means, if the two front wheels on the front axle lose traction completely (free spinning the same time), there will be no power (torque) transferred to rear axle.

Open diff's and since back tires aren't the same speed as the front, the Trac brakes the spinning front and all power goes to the rear. Works perfectly.

 

All differentials are open on the 4WD model. I am seconding this since I have seen it incorrectly stated that the center diff is a viscose cooupled unit which is false.

 

Okay, got details of the Highlander differential from a Toyota training manual:

Highlander differential system

Lars is correct that the center differential is not viscously coupled.

 

Okay, got details of the Highlander differential from a Toyota training manual:

Highlander differential system

Lars is correct that the center differential is not viscously coupled.

So, since the AWD system is not viscously coupled, we should be fine to run different sized tires on our Highlanders, right? According to http://www.4x4abc.com/4WD101/diffautoAWD_AWD.html, this seems to be the case.

I have seen some people post on here stating that you will destroy the AWD system if you use different sized tires (like by rotating the spare into the mix, for example). I am not overly familiar with AWD systems as this is my first vehicle that is not a FWD vehicle. People at the stealership are sure eager to sell you four new tires if one is worn out. This does not appear to be the case with newer AWD systems like in the Highlander. If I am looking at this wrong, please let me know.

 

I found this one, http://www.4x4abc.com/. Hope it can help.

 

The traction control doesn't have a perfect algorithm. Its there to assist. It is no way an effective locker when a real locker is needed. It has torque limitations like any TCS. For 99% of the on-road issues, it works perfectly. Exceed the limitations off-road and you're simply going to get stuck.

Now all we need are LSD's to make up for the torque limitations of the traction control system.

 

Now all we need are LSD's to make up for the torque limitations of the traction control system.

Good luck with that. Toyota doesn't even offer them anymore on the trucks. They all come with Auto LSD now which uses the brakes...same as the traction control. But I will say I wouldn't mind having the traction control on my Tacoma since the HL way outperforms it in the snow (even with the Dunflops as far as driving...it just doesn't stop as well as my truck due to the tires).

 

I just had the 5k service completed at a Toyota dealer and the spare tire was not included in the rotation. The stated reason was, as mentioned above, unequal tread depth having adverse affects on the 4WD system. However, it certainly would seem that Toyota Motor Corp would know 'better' than a dealer. My personal opinion is a five tire rotation isn't worth the time, hassle or money.

 

I hope, for your sake, that your Toyota stealership is better than mine. I could go into details, but, to make a long story short, my most recent bad experience with them was that they do not appear to know how to measure tire tread depth...including the service manager. I knew that I should not have went there for my safety inspection, but since I was getting other things done, I figured, why not? I should have known better.

In regards to the hassle of rotating 5 tires instead of four, the only additional labor involved is dropping the spare, which takes no more than a few minutes. Aside from that, you still need to take 4 wheels off and put 4 wheels on. I do my own rotations, so it really isn't much extra effort. And since the manual says you can do it, is the mechanic or service advisor saying that the manual is wrong? I sent an email to Toyota just to get clarification on this issue, but I would think that if using different sized tires was to mess up the AWD system that badly, that the manual wouldn't be telling you to rotate with the spare.

 

I do not plan to rotate my "spare". I will rotate front to back keeping tires on the same side. When it becomes time to replace my tires I will purchase 4 only. If I ever need to use my spare it will only be in service until I get my flat fixed. Rotating your spare in is a complete waste.. and means you buy tires in sets of 5.. in my opinion

 

I agree with Ralph, rotating the spare seems like a compete waste of time and money.

 

This will be one of things that some swear by and some don't bother. I just don't see it as a waste of time and money. Well, perhaps time, being an additional 2 or 3 minutes work per rotation, but money? If anything, it will save you money as it will allow your set of tires to last longer, rather than having a 7 year old tire that has never been used but is all cracked and cannot safely be used. Also, when it comes to buying a new set of tires, you could buy five new tires, or, you could just buy a set of four, and use the best of the five worn out tires as your spare, and cease rotating your spare into the mix at that point.

At the end of the day, I have a spare that is close to being worn out (good enough for an emergency, since I would be looking for a tire place right after a blowout anyway), lasted a bit longer than your identical tires since I rotated in the spare, and would need to be replaced in about 7 yours or so due to age; and you will have a brand new spare that would only be used in emergencies and would need to be replaced in about 7 yours or so due to age. Neither way is wrong, just preference.

 

I don't understand why someone wouldn't rotate 5 tires if you have a full size, identical spare. You get 25% more life out of the set, so buying 5 later is a wash. The biggest advantage is if you have a significant problem, like a slipped belt or something on one, you can simply stop rotating in the problem tire and go on with the other 4. Using the bad tire for emergencies only. The alternative is a potentially a tire with significantly more tread than the others or buying a complete set of 4 prematurely. The other reason I do it is because tires don't last forever. 7 years is the maximum recommended age for tires.

I like knowing my spare is there, matches the others, and in good shape when I need it. It doesn't cost me anything to rotate it in, other than 2 minutes of my time every 2500 miles. Just my 2 cents.

 

I like knowing my spare is there, matches the others, and in good shape when I need it.

Plus you know the bolts holding the spare under the car aren't rusted and seized. That would be a PITA to deal with on the side of the road.