[3rdgeneration]

That's the same reason that when there is traction, like dry pavement, the wheels can bind when you're fully locked: The inside wheels turn at the same speed as the outside wheels. That can cause problems so that's why you're not supposed to have it fully locked when you have traction (and want to make turns, that is ).

This is a quote from Stargazer from the first page of the thread.

I will fully admit I am new to this AWD thing. As my experience comes from RWD Mustangs. However, Ackerman steering always comes into play when taking a corner. Ackerman steering, simply applied, means the outside wheel while in a corner will always have to rotate faster than the inside in order to complete a corner. Ackerman also relates to the amount of "turn in" the inside wheel has as compared to the outside, basically you want more turn in on the inside wheel as opposed to the outside. Never the less the aforementioned statement contradicts Ackerman steering. Stargazer, are you saying that in an AWD vehicle that it is possible to actually rotate the wheels at the same speed (inside and outside wheels) while in a corner?

Thanks for any input!

[flatthump]

Originally Posted by 3rdgeneration

Stargazer, are you saying that in an AWD vehicle that it is possible to actually rotate the wheels at the same speed (inside and outside wheels) while in a corner?

Thanks for any input!

Dont forget we have diffs inbetween outside and inside wheels.

If you has a strong enough LSD you could easily lock them up in a turn.

[flatthump]

Originally Posted by 3rdgeneration

the wheels can bind when you're fully locked: The inside wheels turn at the same speed as the outside wheels. That can cause problems so that's why you're not supposed to have it fully locked when you have traction (and want to make turns, that is ).

Its the FRONT and REAR DIFFS that spin at the same angular velocity when the DCCD is locked. That is why you shouln't lock it when making a U-turn etc...

Like I said in the post above...our front and rear diffs can act openly to allow the left and right wheels to spin at different rates..

[SilverSurfer]

Good thread. I liked my dccd on my MY04. I used it in much the same manner as the person in the first post (50/50 in snow - more than 1-2 inches, auto rest of time, 35F / 65R stupidery).

I just got my MY07 at the end of March and I'm curious to see how it handles differently in the winter conditions I see in IL due to center diff change and also I believe the front diff is different on the MY07 (helical) compared to the MY04 (sure trac).

[variable]

So, ok I've been trying to understand all this and I think it comes to this in my understanding of things (being a noob and all): It's not a 50/50 split because the tires may not technically be getting the same ammount of traction... however, being that the diff is locked, you're getting the same ammount of, lets just say 'power' to all the wheels. So if you were to put it on a 4 wheel dyno with exactly the same ammount of resistance on all the wheels, you could in theory measure the torque at each wheel as equal.

I think the confusion, at least for me, is/was that wheel speed and torque aren't necessarily related. I think the manual which says 50/50, is a simplification of whats going on so that people will understand the general effect of setting it to lock, i.e., setting it to lock is 'like' setting it to 50/50 because of what you gain by doing it. Does that make sense or am I off my rocker?

[Loubaru]

so is the 41-59 the ratio when it is in lock? what range does the diff work at? like if it is full open can it send all the power to the rear (assuming the rears aren't getting traction, kinda like one tire fire but thinking only about the front and rear)?

[Loubaru]

Originally Posted by CKLewis

so is the 41-59 the ratio when it is in lock? what range does the diff work at? like if it is full open can it send all the power to the rear (assuming the rears aren't getting traction, kinda like one tire fire but thinking only about the front and rear)?

anyone?

[mxpop]

Does anyone know what the increments represent for each setting?

[gregsachs]

you need to be _very_ careful about terminology here. Torque is twist, power is torque*rotation.
On to your question: the diff has a mechanical torque split that functions always except for lock. this ratio is 35/65 or 41/59 after 06. The torque split is only fixed at that ratio in a _non_slip condition, due to the limited slip mechanism, which will steer torque to the slower end. In open, the 04/05 can send all _power_ to either end, for example with one end on ice. However, the _torque_ will be sent to both ends via the 35/65 ratio. The 06/07 shouldn't do this as they also have a limited slip assembly in the diff, designed for roughly 10% of the torque. This would be damaged by large amounts of slip front/rear.
Lock is an odd situation, because you _can't_ pin the torque split. It is nominally 50/50, but will continuously vary based on traction available. for an example, with front on ice and rear on tarmac, in lock the torque split would be close to 0/100, as the front would have no resistance.

(for torque vs power, consider a bolt and wrench-when trying to undo it, you are exerting torque _only_ until it breaks free. once it breaks free and is turning, you have power)

[holycow]

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.

totally wrong. How much torque goes to either the front or the rear, is dependant upon how much traction that side gets.

Here is a scenerio. Pretend your STI is in full lock. The font tires are on dry pavement, and your rear tires are on hard ice. The second you give the car gas, 100% of your torque (or very close too it) will be at the front tires. You cannot put ANY torque to the rear because its on ice and has no traction.

If you spin the car around 180 degrees so the front tires are on ice and the rears are on pavement, without toucing the diff (still full locked) 100% of the torque would then be going to the rear.

So in full lock, your torque split always matches natually occuring traction split the car is experiencing at that moment. Why? because you cannot apply torque to something that doesn't resist back.

[variable]

I think what's basically being said is that if you don't have resistance, you can't apply torque to it (or rather you can't measure it). Right?

[holycow]

Originally Posted by Rootus

No 50/50. No split. Lock = no differential. Also, not all wheels turn at the same speed, just the front & rear shafts. Each end still has a differential and therefore side-to-side wheel speed can differ.

I don't think so. I'm pretty sure the whole system is locked, and you lose the front and rear diffs as well. Ever tried to turn a locked STI on pavement? The reason why it binds and bucks is because when you turn, your inside tires spin at a slower rate than the outside tires. If what you say is true, then this wouldn't happen.

[holycow]

Originally Posted by CKLewis

so is the 41-59 the ratio when it is in lock? what range does the diff work at?

When in lock, there IS no range. Your torque split completely depends on how much traction that tire has to work with.. period. Stop using 50/50 for a locked diff... that's not how it works.

[variable]

This is one of those weird concepts thats difficult to visualize and simplify because we see that all the wheels spin at the same rate when driving in a straight line.

If you put the car in the air, or better yet, on a dyno, would you actually find that the wheels spin at a different rate because of the lack of resistance?

Numerically speaking, assuming your front and rear diffs were locked (easier for this example), if you have say 100ft/lbs with no parasitic loss, with at 41/59 split, you would have 41 ft/lbs at the front and 59ft/lbs at the rear (41 and 59 being percentages in this case). But again, thats weird to visualize because your wheels on the ground will be spinning at the same rate. I'm pretty sure that split divides the HP the same way as well (makes sense in my head anyway), so if your 100ft/lbs were instead 100hp, the numbers would work out the same. *I think*

I haven't looked in the manual in a while, does it actually say 50/50 in there?

[holycow]

Originally Posted by variable

thats weird to visualize because your wheels on the ground will be spinning at the same rate.

torque has NOTHING to do with rate of spin.