ATBs or Torque Biassing Diffs and how they work

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Originally Posted by tact

So I wanted to kick off a thread that discusses and dispels myths around how torque biassing diffs work.
One such myth goes like this:

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Of course it [ATB] does require wheel spin or on the road differences in wheel speed, otherwise you can't have torque differences on a differentiating diff.

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A good read at the torsen site. Torsen(R) Traction gives the reader a good accurate steer regarding this. Especially this part:
"Torsen® differentials are torque-biasing, meaning they distribute torque between the tires – biasing more torque toward wherever it’s best used – without requiring a loss of traction to operate."

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Whoa, you've selected that quote from Torsen as gospel but ignored the quotes from Detroit and Ashcroft as "dumbing down" or something similar. Torsens example is correct in the sense, per the quote above, of differences in wheel speed, but whether that difference across the diff come from differences in wheel speed from turning a corner or losing traction on a wheel as per the Detroit and Ashcroft manufacturers who pitch at 4wds or Quaife and Torsen who also pitch at race cars. Actually, the quote above is incredibly correct despite everything here that I've read. From what I can read, I think the only debate we have is really the amount of torque biasing when wheel speeds are the same, I think there is none, you can't bias 50/50, you think there is some, but in the end there is not a lot of difference until there is a difference in wheel speed across the axle.

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Originally Posted by AK83

The slip that is needed is relative. Not actual wheel slippage, but slippage relative to each axle. Why I found that the 2:40 mark on that video made the difference for me.

That is, the wheel/tyre doesn't slip on the actual road, it's slips relative to the other axle.
I think this is where the misunderstanding happens.

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That's exactly it, thank you. The diff responds to differences in wheel speeds across the axle with torque biasing to resist the differences.

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Originally Posted by rangieman

If this is how good they are and if you could believe the vid why would you bother honestly[bighmmm]
Just one positive locking diff would have walked that[wink11]
Read the comments[bigwhistle]
Discovery 2 off road axle twist with Ashcroft ATB Diff (useless) - YouTube

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At the exact moment that you want that diff to be working the most. The more you need it, the less an ATB diff will help.

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Originally Posted by Beery

It funny how the naysayers always pick out the 0.01% of kilometres travelled where front/rear difflocks would be superior (even that's arguable because you can't steer when your diffs are locked). But never mention the 99.9% of kilometres where difflocks are useless.

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I think it a bit each way........

As soon as a locker thread is started the pro lsd and unlocker owners pipe up

The way I see it is when you outlay good money on a solution very rarely does that person knock or criticis their investment.

I find most people thag naysay arb lockers have never had them fitted.

Re: steering with locked diffs, rear only never and issue, with front and rear engaged a depends on surface....based on my experience.

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Originally Posted by weeds

I think it a bit each way........

As soon as a locker thread is started the pro lsd and unlocker owners pipe up

The way I see it is when you outlay good money on a solution very rarely does that person knock or criticis their investment.

I find most people thag naysay arb lockers have never had them fitted.

Re: steering with locked diffs, rear only never and issue, with front and rear engaged a depends on surface....based on my experience.

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Very true, everyone's got their favourite flavour.

As always it comes down to intended use. For me its general driving, carrying and towing heavy loads with four wheels on the ground, where ATB's are assisting, preventing, working all the time.
Weekend warriors who deliberately look for the hardest tracks to take won't be happy with anything less than difflocks.

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Originally Posted by weeds

.....

I find most people thag naysay arb lockers have never had them fitted.

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Actually! .. I will, but with a specific comment in mind.

My brother's D2 has front and rear ARBs, compressor and all that jazz.
Fitted by previous owner somewhere down the line.
His is a 2003, and therefore has no CDL mechanism.

So my comment re the ineffectiveness of ARBs is .. specifically! .. why on earth would you throw close to $3K on axle diffs, when the CDL can't be locked!
Amazed me that someone would think along those lines.
ps. I'm always on his case to either get an ATB centre or to start the process of getting my spare D2 transfer case (with mechanism) fixed, so that we can sort that out for him

Anyhow .. twin locked axles and no CDL, relying only on traction control .. just doesn't work(well).
It kind'a sort'a worked, but only after a lot Jeremy Clarkson attitude .. powwwerrr!
Doing that had the front axle spinning madly or the rear axle spinning madly trying to climb a not too difficult rock ledge.

So, to be clear here, I'm not blaming the lockers for being ineffective, and I have no issue myself with solid lockers, just the inappropriate installation of them.
Brother is a bit of a off roading newbie compared to most of us here, had a Patrol for about a year prior to the D2, but limited experience off roading with it.

Once I have my ATBs fitted(F and R), I want to try to get back to the spot and compare how they each compare but without the use of the CDL in my D1 too.

In the video posted by rangieman, at the 1:25 mark in the video you can clearly see that the chap didn't have the CDL locked, and the front wheel spinning for a sec or two.
He says he only has the ATB in the rear. So clearly he doesn't fully understand their dynamics properly.
At the start(about 4-5sec mark) it does appear that both rear(left) and front (right) seem to be spinning at the same moment tho, so he obviously has the CDL engaged.
But after that he seems to have unlocked the CDL for some reason.
So the traction control in the D2 seems to take too long to react to the spinning wheel .. which is what I saw with brother at the rock shelf with both axles locked too.

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Originally Posted by weeds

I think it a bit each way........

As soon as a locker thread is started the pro lsd and unlocker owners pipe up

The way I see it is when you outlay good money on a solution very rarely does that person knock or criticis their investment.

I find most people thag naysay arb lockers have never had them fitted.

Re: steering with locked diffs, rear only never and issue, with front and rear engaged a depends on surface....based on my experience.

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Similar, my experiences are that they do steer twin locked but they can push a little bit.

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Originally Posted by AK83

Actually! .. I will, but with a specific comment in mind.

My brother's D2 has front and rear ARBs, compressor and all that jazz.
Fitted by previous owner somewhere down the line.
His is a 2003, and therefore has no CDL mechanism.

So my comment re the ineffectiveness of ARBs is .. specifically! .. why on earth would you throw close to $3K on axle diffs, when the CDL can't be locked!
Amazed me that someone would think along those lines.
ps. I'm always on his case to either get an ATB centre or to start the process of getting my spare D2 transfer case (with mechanism) fixed, so that we can sort that out for him

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Absolutely! When the D2 came out there was a lot of discussion about the lack of CDL and people were getting into trouble, notably with failed ascents, having the front locked up and then coming unstuck on the way down. In general the thinking back then also was always CDL and then F&R diffs.

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Originally Posted by Beery

Yeah so, a few things, the guy making that vid obviously doesn't understand how they work by the way he is describing 'atb reaction times'. Also says he only has one ATB in the rear and that the centre diff was only locked for part of the video.

The ATB doesn't really have what he calls a reaction time. Obviously when a wheel is off the ground, there is zero torque to that wheel. So is actually waiting for the traction control react, to apply some resistance to that wheel. With all wheels on the ground, the ATB does all the work before the traction control even realises there is a problem 99% of the time.

I think having the centre diff locked and another ATB in the front would have made that crossing a lot easier.

Its funny how the naysayers always pick out the 0.01% of kilometres travelled where front/rear difflocks would be superior (even that's arguable because you can't steer when your diffs are locked). But never mention the 99.9% of kilometres where difflocks are useless.

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Why would you need to buy 2 ATB`s when only one positive locker would suffice in majority of situation`s and cheaper.
I don`t chase the hard stuff but like my choice of locker as much as you do and others [thumbsupbig].
But the argument is how they work (don`t):Rolling:
You can steer with both positive locker`s engaged that is a furphy that you can`t steer yes it is not good on the drive line but in a pinch you can but it does have a switch that is not hard to use at all[bighmmm],
.
And yes we all try to justify how we spend our hard earned [bigwhistle]
At the end of the day it depend`s how much you want to spend and with out the proper knowledge you end up with a expensive paper weight .

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Originally Posted by rangieman

Why would you need to buy 2 ATB`s when only one positive locker would suffice in majority of situation`s and cheaper.

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One air locker is about the same price as two Ashcroft ATB's.

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Originally Posted by rangieman

You can steer with both positive locker`s engaged that is a furphy that you can`t steer yes it is not good on the drive line but in a pinch you can but it does have a switch that is not hard to use at all[bighmmm],
.

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I hope the heavy duty drive shafts, CV joints and drive flanges didn't cost too much to make that a safe thing to do.

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Originally Posted by rangieman

And yes we all try to justify how we spend our hard earned [bigwhistle]
At the end of the day it depend`s how much you want to spend and with out the proper knowledge you end up with a expensive paper weight .

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ATB's are pretty easy to justify in that they are in play 100% of the time, pre-empting and enhancing the ETC on road, off road, wet, dry, frozen, concrete, bitumen, gravel, sand, mud, grass etc.
For that 0.01% of the time when you don't have all four wheels on the ground makes difflocks hard to justify for most. Even in this case, ATB's are an improvement over open diffs with traction control.

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Originally Posted by Beery

One air locker is about the same price as two Ashcroft ATB's.


I hope the heavy duty drive shafts, CV joints and drive flanges didn't cost too much to make that a safe thing to do.


ATB's are pretty easy to justify in that they are in play 100% of the time, pre-empting and enhancing the ETC on road, off road, wet, dry, frozen, concrete, bitumen, gravel, sand, mud, grass etc.
For that 0.01% of the time when you don't have all four wheels on the ground makes difflocks hard to justify for most. Even in this case, ATB's are an improvement over open diffs with traction control.

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I Don`t have heavy duty front cv`s , axles , or flanges as they are not needed in my case because im not into extreme although the rears are heavy duty which is a sensible upgrade for most rovers as we all know[wink11]
If you feel justified with your out lay all good [thumbsupbig]
By the time you buy 2 Atb`s and get someone to remove set up the diff`s and refit the centre`s the cost will be up there , Not everyone is handy on the spanners [bighmmm]
Atb`s are not for everyone and that should be highlighted openly instead of all the hype trying to justify ownership[wink11]

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Originally Posted by rangieman

I Don`t have heavy duty front cv`s , axles , or flanges as they are not needed in my case because im not into extreme although the rears are heavy duty which is a sensible upgrade for most rovers as we all know[wink11]

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Fair point, the standard ones are pretty rubbish.

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Originally Posted by rangieman

If you feel justified with your out lay all good [thumbsupbig]

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I certainly am, seeing they're useful 100% of the time and not just dead weight for 99.99% of the time but then for 0.01% have an advantage over something else.

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Originally Posted by rangieman

By the time you buy 2 Atb`s and get someone to remove set up the diff`s and refit the centre`s the cost will be up there , Not everyone is handy on the spanners [bighmmm]

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Nope, its a pretty quick job.
Setting up and installing an air locker and then plumbing in the air line properly, installing the compressor and wiring it up and installing and wiring the dash switches all takes time and money too. Like I said, final price about the same for one versus two.

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Originally Posted by rangieman

Atb`s are not for everyone and that should be highlighted openly instead of all the hype trying to justify ownership[wink11]

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That's not the point of the thread. Tact created it to help educate people about how they actually work. A diff lock is a fairly blunt object that is easy for people to understand, where an ATB is a bit more challenging. So I take my hat off to you, you're clearly reading this thread to better yourself.