locked or unlocked when pavement ends?

[JB.]

Can you explain this one further? This is not my understanding of a standard locked 4wd system, power is 50/50 F/R, how does the the locked Torsen allow 100% of the power to go to one end?

I'm not fond of the 50-50 power spit as a description. The phrase could just as easily be applied to an open diff.

For simplification, think of a 2WD with a locked rear diff with one wheel in the air and the other with unlimited traction. The wheel on the ground receives virtually 100% of the available torque. Nothing is being lost to the other wheel.

If the diff were open, the wheel on the ground would receive virtually 0% as the other wheel spun but the torque split at both wheels, for the tiny amount there was, would be 50-50.

The torsen will multiply the torque going to the wheel with the least traction over to the wheel with more, but the multiplication is limited so it has to have some resistance to work with.

A locked diff has no such limitation. Torque just follows traction and the range is virtually 0-100%.

 

[crackiswack]

I'm not fond of the 50-50 power spit as a description. That's what an open diff does if traction is equal.

For simplification, think of a 2WD with a locked rear diff with one wheel in the air and the other with unlimited traction. The wheel on the ground receives virtually 100% of the available torque. Nothing is being lost to the other wheel.

If the diff were open, the wheel on the ground would receive virtually 0% as the other wheel spun. So the range with a locked diff is 0-100%.

The torsen will multiply the torque going to the wheel with the least traction over to the wheel with more, but the multiplication is limited so it has to have some resistance to work with.

I guess I disagree. If a 2wd has a locker, 50% of the torque still goes to the wheel in the air, it simply doesn't do any work to move the vehicle.

 

[JB.]

I guess I disagree. If a 2wd has a locker, 50% of the torque still goes to the wheel in the air, it simply doesn't do any work to move the vehicle.

Imagine that truck climbing a steep hill on pavement. Traction is equal to both wheels so they're sharing the drive shaft torque about 50-50. Then one wheel encounters a strip of smooth, oil covered ice. As long as the other wheel doesn't break traction, the truck would move along just like before with no additional drive shaft torque but the torque split at the wheels would be close to 0 and 100%.

.

 

[crackiswack]

Imagine that truck climbing a steep hill on pavement. Traction is equal to both wheels so they're sharing the drive shaft torque about 50-50. Then one wheel encounters a strip of smooth, oil covered ice. As long as the other wheel doesn't break traction, the truck would move along just like before with no additional drive shaft torque but the torque split at the wheels would be close to 0 and 100%.

.

Your speed would drop, the power in a locker system doesn't shift, it stays at 50:50 regardless of traction. It is the same reason that you can't run with a locked differential on pavement. When you turn the wheels they want to spin at the same rate because the torque application is the same. It is why the wheel on the inside corner breaks traction or binds.

 

[JB.]

Your speed would drop, the power in a locker system doesn't shift, it stays at 50:50 regardless of traction.

The amount of torque applied to the ground remains virtually unchanged, it just shifts to one wheel. There's nothing to cause speed to drop.

 

[crackiswack]

The amount of torque applied to the ground remains virtually unchanged, it just shifts to one wheel. There's nothing to cause speed to drop.

Upon further reading, this is correct. While both wheels continue to spin at the same rate but the torque at the wheels is only applied to the wheel with traction. Darn semantics :bigok:

 

[03_4x4Runner]

Hey everyone, i'm relatively new to this forum as i just purchased my 4runner last October. Since then, I've taken it out about 4 - 5 times (mojave road, anza borrego, big bear, and lone pine area).

So far this is what i've been doing. As soon as pavement ends, but on a decently maintained dirt or gravel road, i put it in 4hi unlocked. I pretty much keep it in this mode unless i climb a steep hill, hit soft sand, or expect mud.

i've gotten stuck a few times, once in sand and once in mud, and i would switch to 4lo unlocked, and if that doesn't get me out, i would lock it in 4lo. Luckily that has gotten me moving after some major revving and once i get some momentum i eventually got out.

Is this what everyone else is doing? Or do you guys lock it in 4hi much earlier? The only reason i'm hesitant to lock earlier is because I want to compromise handling and be able to take sharper turns.

I've read somewhere that unlock mode is actually better on snow, but lock is definitely better for mud and sand.

Any thoughts and feedback on ths topic would be greatly appreciated!

I have run this same type desert/mountain terrain many times and many miles. I seldom lock the center dif. You are right leave it unlocked to prevent binding and use lo range as needed. In very steep or loose sections lock the center dif. If you are in deep sand you almost have to keep it locked or the traction control kicks in and tries to bring you to a stop. With the center dif locked you can keep the tires spinning faster to get you through. Do not wait till yoiu are stuckto do this or you may not be able to get out.

 

[CAN-03runner]

Are you assuming the ATRAC would brake the front wheels to allow torque to transfer to the rear? Have you confirmed this actually happens and is benefitial, ie the transfer of the power to the rear wheels overcomes the additional drag on the front wheels from the brakes being applied?
Edit: N/M the Torsen continues to work as long as there is some traction, it only completely fails when a set of wheels loses complete traction

The Torsen is mechanical and always sensing torque difference. The limitation on a 4th gen runner with a Torsen is 30/70. Trac just further aides this braking a spinning wheel. Full blown A-Atrac comes on with the center locked in low range. So Torsen is not TorqueSensing.

 

[CAN-03runner]

Are you assuming the ATRAC would brake the front wheels to allow torque to transfer to the rear? Have you confirmed this actually happens and is benefitial, ie the transfer of the power to the rear wheels overcomes the additional drag on the front wheels from the brakes being applied?
Edit: N/M the Torsen continues to work as long as there is some traction, it only completely fails when a set of wheels loses complete traction

I haven't consciously tested the same hill climb with center locked and center unlocked to see which was smoother or better. But I do switch between the 2 on the trail just to check it out. I have only ever gotten stuck in mud. There was no hope. Except taking a run for it. But I'm not into that. I might say over 80% of the time center unlocked in 4lo would be enough. But I keep center locked most of the time because I don't want to be "that guy" my buddies post up on YouTube.

 

[crackiswack]

The Torsen is mechanical and always sensing torque difference. The limitation on a 4th gen runner with a Torsen is 30/70. Trac just further aides this braking a spinning wheel. Full blown A-Atrac comes on with the center locked in low range. So Torsen is not TorqueSensing.

Can you expand further? I'm not clear on what you are saying. My understanding of the Torsen unit is that it shifts torque to the axle with more traction by multiplying the torque on the axle with less traction by some factor(5?) so if the front has no traction(certain instances when hill climbing) then the torsen fails to properly shift torque to the rear (0x5 is still zero), this I think is where the ATRAC comes into play

 

[JB.]

My understanding of the Torsen unit is that it shifts torque to the axle with more traction by multiplying the torque on the axle with less traction by some factor(5?) so if the front has no traction(certain instances when hill climbing) then the torsen fails to properly shift torque to the rear (0x5 is still zero), this I think is where the ATRAC comes into play

You've got it.

By my <a href="http://www.toyota-4runner.org/4th-gen-t4rs/59289-4x4-questions.html#post490585" target="_blank">reckoning</a> the multiplying factor (torque bias) is 1.8.

ATRAC actually works better without the diff locked because of the multiplying effect which can lead to the conclusion that unlocked is best, but less ATRAC intervention will be necessary in the first place with the diff locked so it's still the most capable traction mode.

 

[JB.]

Btw, if the bias ratio of 1.8 sounds a little underwhelming, I should point out that not only is functionality increased by the rear biased configuration, but the Torsen-C is also extremely durable in all uses, including off-road, and should easily last the life of the vehicle.

 

[K2Runner]

Well, i don't have a locker but i usually go by the motto "If you get stuck in 2wd, you have 4wd. If you get stuck in 4wd, your stuck", just my 2 cents