The differences in turning radius per tire (when turning the car right or left) is definitely why they dont want it turned on on dry pavement, i know for a fact that is why...wish I could convey it better.

I think if you had a 4wd RC truck with one motor, a basic example for sure, but definitely a locked 4 wheel drive system you would understand what i am saying.

You could see that the differential does not allow for slippage between right/left and front/back.. I think each side can turn at a different speed, but thats it.. not each individual tire. Basically the front and rear axles are tied together and turn at the same speed and cannot vary if its forced into 50/50 torque split.

Even if you jack up an X on one side with the engine off, tranny in neutral, you can turn the rear (passenger) tire and the front left will also turn the same speed.. Not sure what this proves exactly.. but it was nearly impossible to turn the one wheel last summer until i jacked up the whole side..

 

I am definitely in agreement with you that the front and rear wheels travel different distances around corners. The car's body is straight, so the rear wheels won't follow the radius through the turn. They will "cut the corner", so to say.

From the transfer case, there is one driveshaft to the front, and one to the rear. The clutch pack in the transfer case is concerned with managing (via the hydraulic pressure) the difference in rotational speed between these two driveshafts.

Although I haven't yet looked into the details of how the viscous coupling differentials on each axle function, I see your point that that slack of the left/right rotational differences that the differential takes will influence the speed at which the driveshafts turns. Hence, sharp turns would cause a greater discrepancy in the rotational speeds of the front vs. rear driveshafts.

 

The G35 has differentials at both the front axle and the rear axle, which allow each tire to turn at different speeds. Check the diagram I posted.

The transfer case only modulates the relative speed between the front and rear driveshafts. When it locks them together (50:50 split), the front and rear driveshaft are forced to turn at the same speed, but the differentials at each axle still allow for each individual tire to turn at a different speed.

 

Are you an engineer, or have any sort of technical background?

 

Mechanical engineer? Not at all. I'm a computer & network engineer.

But primarily I'm just a very curious 24 year old who bought a G35X a week ago

The complexity of the G35X is mind-boggling compred to my previous car, an Acura Integra...which was basically run by a hamster in a wheel.

 

Wow one week and already knowin more about the AWD system than guys who have driven this car for years.

I'm an ME myself

 

I'm still gonna have to go ahead and disagree with ya here... If the differentials, when locked in at 50/50, allowed everything to slip 2 things would be the case


1. The car would not handle the way it does when the snow button is on and vdc is off.. try it out on snow

2. The manual would not state anything about "Do not use the SNOW mode button on dry pavement"


ps. My Pilot and Ridgeline use multiple clutches too, and they are not supposed to be locked into 4 wheel lock on dry pavement either.

 

I'm not too clear on what you meant, geew1z. The differentials in a G35X do not lock. They're viscous coupling units designed to allow the left/right wheels to turn at different speeds, such as when going around a corner. No matter what surface you drive on, cornering will result in a difference in rotational speeds between left/right tires because the inner tires always travel a shorter distance. They are not electronically controlled and function the same regardless of whether SNOW mode is selected or what type of surface you're driving on.

A locking differential is most often found in serious off-road vehicles, and literally locks the left/right wheels together, disregarding traction, rotational differences, etc. They'll lock the differential(s) to overcome large obstacles when there is a big disparity in traction between the left and right wheels.

I didn't say that SNOW mode allowed everything to slip. I agree that in SNOW mode, the front/rear driveshafts are indeed locked together by the clutch pack in the transfer case, thereby always sending 50% of the torque to the front wheels and making the G35X an all-time 50/50 4WD car. Well, up to 20mph at least. Then it reverts back to standard operation.

So yes, there's definitely some logic behind the manual's warning not to use the SNOW mode on dry pavement (although it defeats the purpose of being cautious BEFORE encountering a potentially slippery surface, and expects you to wait until you're already on a slick surface to turn on SNOW mode). I don't believe the differentials have anything to do with it, though. It's the front/rear driveshafts that are locked together, not the left/right wheels.

 

The differentials on the X (and non-sport rwd) are not locking differentials. They are open differentials. There is no sort of electronic control here, they are completely mechanical and independant of the AWD.

I think you are confusing our talk of the AWD's transfer case with the function of the mechanical differentials which contain no clutches 9except in the case of a limited slip differential).

But in the case of a G35's AWD system, the differentials are of the open style and do not lock. They do not slip either though, they are mechanically joined.

Some good example animations here.

http://auto.howstuffworks.com/differential2.htm

Technically, if you were to turn the VDC off in the snow, and position your car in such a way that you could get 1 tire up front and 1 tire in the rear stuck...you would not move at all. With your front and rear open differentials, you'd just spin those two tires all day long and never move. Thats the downside of open differentials.

What the G35 has is prob one of the better traction control/stability control systems i've ever driven in the snow. Repeat the exact above situation, except turn the VDC back on. Try to get one and when you start spinning those two wheels, the VDC will apply brake to the spinning wheels. This slows them down as if they are getting traction and beings to force power (by mechanical means through the differentials) to the opposite tires. By varying the brake to the wheels, the VDC almost creates a situation where all 4 wheels "lock" in a sense. It would do the same in a RWD car with an open diff as well. It would take the wheel that is spinning, and stop it forcing the opposite wheel to start to turn where it normally wouldn't.

This is all done by varying the pressure of the clutch disks in the transfer case (in this case, 50:50 ratio) and manipulating each wheel brake to control spin and force power through the differential to the opposite wheel.

Like i said before, the Infiniti AWD and VDC are two different systems, but they work together very well.

 

huh.. ok. I see what you guys mean by not actually being locking differentials now...

I still wonder why then it is not to be driven on dry pavement then. If all of the wheels can turn at their own rate, then it shouldn't matter unless its just because that clutch is sending equal power to the front and rear axles and the sum of the rotations of the rear wheels compared to the front wheels is different, so then it becomes a stress on that clutch..

 

Yea, I think that is pretty much the reason. Front and rear driveshafts are locked together with 288psi of pressure on the clutch pack. So any rotational differences between the front & rear driveshaft (exaggerated when tire diameters aren't all exactly the same and while turning) would have to be absorbed by this clutch pack as heat. The question is really how much slip it is designed to withstand. I'm sure there is some tolerance, since I drove it in SNOW mode a few times on dry pavement and lived to tell about it. But it makes a lot more sense after this discussion why it wouldn't be recommended to constantly do that, especially if you're under 20mph frequently.

This explains the tire slip I felt when turning out of the gas station into the street while SNOW mode. There was a little bit of loose gravel, and I had the wheel cranked to the right to pull out. Giving it just a little bit of gas caused some wheel slip. Now I know that it was due to the fact that I was in SNOW mode, and the tire on the loose gravel was the weakest link to absorb the front/rear rotational difference. Without the loose gravel, traction would've been higher and it would've been the clutch pack that would have had to absorb it.

I think we've figured it out. Needless to say, I do not drive in SNOW mode anymore.

 

I asked one of the Infiniti Tech last year about SNOW Mode, he said the system does set the drive train at 50/50 until between 15-20 mph, but also starts you out in 2nd gear, so as to maintain traction in snow on initial takeoff, rather than 1st gear... just like they tell ya in Driver's Ed. and how to drive in snow. That's why the car feels a bit bogged when in snow mode.. you're in 2nd gear man!

Otherwise as most everyone else has stated, the AWD system will eventually go to RWD at highway speeds, until it senses something's not right, then dynamically adjusts power to all the wheels according to your driving style, road conditions and whatever is going on at the wheels.. that's the beauty of it!

 

Believe it or not, the Infiniti tech is wrong. SNOW mode does not start you off in 2nd gear. The only two things it does are (1) reduces throttle sensitivity (the car is is drive-by-wire) and (2) fully engages the front driveshaft for a 50:50 torque split up to 20mph.

You can read threads on this forum which confirm this. And you can confirm yourself by just popping into manumatic mode while the SNOW button is on: you'll see that you're still in 1st

 

So i think we've discovered the absolute worst thing to ever do on your G35x

With sticky tires, turn the snow mode switch on, cut the wheel to full lock...and drive in the sharpest circle you can on dry asphault (summertime would make it hot and stickier too)

Poor transfer case

 

but does dropping it into manu-mode, overide the auto-mode 2nd gear setting while in snow mode...?