[supermarkus]

As a thought experiment, if I were to put 100 lb-ft of torque through the input shaft of the center diff at full lock, what would the measured torque be at the output shafts, isn't this still dictated by the gearing of the center diff despite both outputs rotating at the same speed?

[flatthump]

Originally Posted by supermarkus

As a thought experiment, if I were to put 100 lb-ft of torque through the input shaft of the center diff at full lock, what would the measured torque be at the output shafts, isn't this still dictated by the gearing of the center diff despite both outputs rotating at the same speed?

No, it's dictated by the amount of resistance on each side of the vehicle. The only amount of torqe that can be applied to a wheel with Zero traction is the force that's required to accelerate a mass(the wheel).

Edit: You said if you were to measure the torque, which means you would be applying resistance to get the reading, it would be dependent on the gear ratios.

[JAYMAC10]

Originally Posted by mxpop

After many track day/races, I found that no single setting does as much good for me as auto. It becomes a distraction to mess with it between sections and it can mess you up if you dont get it switched properly and quickly enough.

It's funny how I like to brag to people about being able to control the center diff but in reality, I never touch it.

I think Subaru put that dial in their just so they can charge another few thousand $$ for the car!!! hahaha

I find myself doing exactly the same thing... However, I do like to put it to open in the winter and have some fun!


Jay

[mxpop]

I would use winter settings in BC too if I lived there.

My "winter" consists of a little rain and the locals forgeting how to drive....

SoCal

[Ozer]

My dear friend, if the front tires or on tarmac and have full traction, where are they spinning? How is that possible? If they have to move at the same speed, and if the rears are not able to put any torque to the ground, then I hope you can imagine where most (close to 100%) of the torque is going to...

Originally Posted by Stargazer

In that situation, being fully locked means that the front wheels will spin at the same speed as the rear wheels, therefore getting you out of that spot--not really anything to do with moving the torque to the front.

[Stargazer]

Originally Posted by Ozer

My dear friend, if the front tires or on tarmac and have full traction, where are they spinning? How is that possible? If they have to move at the same speed, and if the rears are not able to put any torque to the ground, then I hope you can imagine where most (close to 100%) of the torque is going to...

They wouldn't be spinning because they're on tarmac. So you'd be moving forward. Just like the rears wouldn't be spinning because they're rotating at the same speed as the fronts--moving you forward. You might be confusing torque with "traction". Just because a spinning wheel has no traction, doesn't mean that it's spinning with no force. The only way that there would be no "torque" is if the rear wheels weren't spinning at all--just sitting still. Which doesn't happen when the DCCD is locked.

[flatthump]

^That torque is available at the rear end. However it is not being applid in that situation because there is no resistance.

[Stargazer]

Originally Posted by flatthump

^That torque is available at the rear end. However it is not being applid in that situation because there is no resistance.

OK, I'm not a mathematician or a scientist, but my understanding of "torque" is that is a rotational force. It measures the amount of force required to turn something. Torque measures only rotation and NOT how far forward your car moves.

Check out this for a full explanation of torque vs work: http://craig.backfire.ca/pages/autos/horsepower

If torque "is not being applid [sic]" then there is no torque. But that's NOT the situation here. Just because your car is not moving forward does NOT mean that there is no torque to the wheels that are turning.

If you're talking about a simple 2WD system with no traction control, where one tire is stuck on ice and the other is on dry pavement this is what will happen when the driver tries to accelerate: The tire on the ice will spin. The tire on dry pavement will sit still. The tire on the ice is spinning because it is getting all the torque. The tire on pavement is not spinning because it is not getting any torque.

On Subarus with 4WD and a locked DCCD, all tires spin at the same rate so all tires get the same amount of torque: whatever Subaru engineers have programmed, be it 40/60 or whatever--it doesn't change.

[lackskill]

Originally Posted by Stargazer

If you're talking about a simple 2WD system with no traction control, where one tire is stuck on ice and the other is on dry pavement this is what will happen when the driver tries to accelerate: The tire on the ice will spin. The tire on dry pavement will sit still. The tire on the ice is spinning because it is getting all the torque. The tire on pavement is not spinning because it is not getting any torque.

I know I am nitpicking, but traction control has little/nothing to do with this. Its a function of the type of differential. An open diff will act in the manner you described. Our subaru uses 3 limited slip differentials. They will try to apply torque evenly to all wheels as designated by gearing.

Originally Posted by Stargazer

On Subarus with 4WD and a locked DCCD, all tires spin at the same rate so all tires get the same amount of torque: whatever Subaru engineers have programmed, be it 40/60 or whatever--it doesn't change.

This is what I have been trying to tell people for what seems like forever. Torque distribution is a product of gearing. The amount of lockup or slip of the DCCD does not change the torque distribution. 35% (on an 04/05) still tries to go to the front wheels even when the DCCD is operating at its lowest lockup setting (commonly referred to as "open", however it isnt. It always has some lockup).

[Stargazer]

Originally Posted by lackskill

I know I am nitpicking, but traction control has little/nothing to do with this.

That's exactly why I left it out . I wasn't referring to Subaru's in that 2wd example--I was thinking more of my '88 Tercel .

[Ozer]

OK, this is my last post. If a tire is not spinning, yet there is no traction, it means there is NO torque currently applied to the tire. If there was, then the tire would spin! If, however, the car is moving, you guys should ask yourself: where is the torque being applied to if rears have no torque? Of course, at this example, to the fronts, where the front tires are on normal tarmac, (and rears are on ice). Locked central differential is like solid pipe.

Yet another example: put 4 rubbers onto a solid piece of pipe and make only one of them touch the ground. Then start rolling the pipe (keeping only one round rubber touching the gorund). Of course, there is a torque being applied, but only by the touching rubber EVEN THOUGH all the other rubbers are also turning at the same speed. So what? Let them turn; they do NOT apply any torque to the ground; period.

After all these examples, if you still suggest that a locked differential would apply same torque to all the tires or whatever gear ratiio (41/59), I rest my case

[Stargazer]

Originally Posted by Ozer

OK, this is my last post. If a tire is not spinning, yet there is no traction, it means there is NO torque currently applied to the tire. If there was, then the tire would spin! If, however, the car is moving, you guys should ask yourself: where is the torque being applied to if rears have no torque? Of course, at this example, to the fronts, where the front tires are on normal tarmac, (and rears are on ice). Locked central differential is like solid pipe.

Yet another example: put 4 rubbers onto a solid piece of pipe and make only one of them touch the ground. Then start rolling the pipe (keeping only one round rubber touching the gorund). Of course, there is a torque being applied, but only by the touching rubber EVEN THOUGH all the other rubbers are also turning at the same speed. So what? Let them turn; they do NOT apply any torque to the ground; period.

After all these examples, if you still suggest that a locked differential would apply same torque to all the tires or whatever gear ratiio (41/59), I rest my case

OK. This will be my final post, too .

You didn't read that link I posted did you? There's a lot there, but if you just look at the beginning, it explains what torque is and how it is calculated.

"Torque is a force that tends to cause a rotation. A force applied at a non-zero distance from an object's centre will tend to rotate the object. This is easily seen in real life. If you put a wrench on a bolt and pull on the end of the wrench, the bolt will turn."

Using your own example, if the tires are connected to a solid pipe, how is it possible that the rotational force on one end is different than the rotational force on the other end ? What I think you're trying to explain is that there is no POWER to the spinning wheel.

This is how Power is calculated:

First, "Work is defined as the transfer of energy from one system to another, such as a person pushing a box across a floor."



"Torque is a force that causes a rotation, which means that it does not actually cause an object to move along a distance. Therefore, torque is not work."

Work is caused by torque.

So, this chart describes the relationship between work, torque, and power:



Using simple math it's easy to see that a spinning tire that is not moving forward (i.e. distance=0, work=0) does NOT mean that there is no torque (rotational force). It DOES mean, however, that there is no power.

Oh, BTW, torque is applied to the wheels. I think trying to apply torque to the ground would be quite futile given the earth's large size .

[flatthump]

I'm actually studying for my M.E. degree and this little math problem has me kinda stumped. Feel free to completely call me out on this.

Stargazer all that math works out but I think one thing we left out is that Force=Mass*acceleration. Im pretty sure Mass in this case would include a portion of the cars Mass. On the other hand, if a wheel if off the ground(or cant apply force to the ground) then it is not contributing to the acceleration of the body.(only the acceleration of the wheel, rotor etc...plus we know with a locked diff, front and rear acceleration are equal to eachother)

But if that wheel can apply force to the ground, than the Mass must include a portion of the car's mass. The force applied to the ground, or rather the reaction to it, is what actually causes the body(car) to accelerate.

So if we dont have force applied to the ground then the mass is only the Mass of the wheel/rotor etc..(For simplicity, lets consider this Zero right now)

Since we dont have Mass we dont have any Force either.(Force =Mass*acceleration)



Imagine that the rear end is off the ground with the center diff locked. Acceleration is directly porportional front and rear(with our locked diff) so let "1" represent acceleration to make this even more simple.

Using Force=Mass*acceleration,

The front end has 100% traction so the mass is the mass of the car. Lets say 2010kg.
The rear end is not accelerating any Mass.(realistically it is but we called it zero because it is very small compared to the mass of the car).

Front end----Force=2010*1= 2010
Rear end-----Force=0*1= 0
If we dont have force than we dont have torque. (Torque= Force*Length)

[flatthump]

I'm positive actually.

With a perfectly locked center diff, the front and rear is forced to spin at the same angular velocity. It's determined by the gear ratio.(as long as that baby stays locked)

If we must keep equal angular velocity front and rear, but at the same time have varying loads, then torque is inevitabley 'transfered'(proportionally) to the side with a greater load.

Torque will be 'transfered' appropriately in order to turn the two out-put shafts at equal angular velocities.

The torque 'transfer' I mentioned above has NOTHING to do with the DCCD. My example was with a completely locked center diff. The torque 'transfer' I described is soley the product of physics.

[Stargazer]

I think it's becoming a matter of semantics because I don't think we're talking about the same thing. Torque is a ROTATIONAL force and it doesn't not describe linear movement. I guess I'm just not very good at explaining the information about horsepower and torque that's on this page:

http://craig.backfire.ca/pages/autos/horsepower

Oh, yeah, I'm sorry that I lied about not posting again .