Thread: ATBs or Torque Biassing Diffs and how they work

Originally Posted by tact

Started this thread to discuss how torque biassing diffs work and to dispel myths. Tackling these topics inevitably includes comparisons to other traction aids and that’s ok. (Not in a childish “mine’s better than yours” way, but more in a “this wine is sweeter than that one, that wine is dry, choose what you like” mindset)

That (can, if we let it) lead to clearly defined strengths, weaknesses, which (can, if we let it) lead to informed decisions as to whether a particular traction aid fits needs. And knowledge of all this can, if we let it, lead to discussing techniques that can be helpful to a degree in overcoming limitations of the ATB.

Appreciate those who understand this and are here to contribute helpfully. Examples are:
The video posted showing a crossaxled disco going nowhere:
- Good one! Being crossaxled, or a wheel in the air, is a situation that is acknowledged as one not handled well by an ATB.
- we can discuss why this is so and how to best drive an ATB, techniques, to keep a vehicle in that situation moving (if that were at all possible).

Commenting on the D2/ATB video “if that’s the best you get from an ATB then they are useless” is spectacularly unhelpful. It’s akin to showing a video of a truck with a full locker breaking an axle and commenting “if that’s what you get from a having a full locker fitted then they are useless” - also spectacularly unhelpful.

We’re all big girls here so ****-taking and good natured retorts are also welcome!

But if you are only here tossing ignorance around because you think that “the only good traction aid worth having is a [insert name]” then that sounds like a great thread topic that you can create and enjoy.

Well done on starting a specific thread.......although near impossible to keep on track. Certainly some good information.

Maybe it could be cleaned up and transferred to the good oil

In my previous car (very modified Great Wall X240) I had a Detroit auto locker in the rear and a torsen type locker in the front. The front locker was made in Russia, and I am sure Jacden, member on this site can give you details. The front locker when in 4wd was not really noticable in forward motion. However it was almost impossible to steer the car in the following situation. When in reverse and going up a hill, Ie under load, steering was extreemly hard. So much so that the only way to steer was to back off the speed and then turn the wheel at the same time. The thing I liked about my lockers were that no one knew you had them, and there was no need to guess or anticipate do I need to have the lockers on? As a result, in just about every sticky situation, I would get up or get through first try, whilst others with manual lockers, would have to suddenly realise oh **** I need my locker on and try to quickly fumble for the switches etc. Around town the rear locker would sometimes get wind up and then there would be a "clunk" noise as it released the wind up. After a while you just got used to it and no damage or bits of metal were ever detected in the diff oil when it was replaced.

Originally Posted by tact

Mate there used to be a manufacturer (KAM, I think) who did an ATB guts in a diff with also selectable full locking - for front/rear diff. Just like the Ashcroft ATB replacement for the Defender centre diff, it is still fully lockable. Best of both worlds.

Not an ATB style diff, a plate type LSD.

Wave Trac in the US make an ATB type diff with pre load springs (belville washers) on the helical gears, this helps torque biasing if you lift a wheel.

No, they don't make them for Rover diffs, they are aimed at motorsport, e.g. a Mustang lifting an inside wheel coming off a corner on the track.

Ashcroft's ATB has more inherent pre load and a 'better' bias ratio than the TruTrac, not sure re the Quaife.

As I've mentioned previously, aggressive TC is the perfect accompaniment to an ATB style diff, allowing it to do its thing and bias torque if one wheel loses traction.

Having said that, I'm **** with TC!
I'm still so old school, if a wheel starts to slip and spin I'm modulating the throttle, searching for grip instead of hammering the loud pedal and letting the electrickery do its thing!
I do the same with ABS, I used to out modulate the ABS in the work BT50 and do the same with the current Hilux!
I had the inside front Michelin howling it's displeasure without triggering the ABS conning into a corner last week.

A good read at the torsen site.

"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."

Originally Posted by Slunnie

[...]Actually, the quote above is incredibly correct despite everything here that I've read.

Just checking I have not misunderstood - Have I got the right incredibly correct quote to which you refer? (above)

It thats the quote then we agree here for sure. That a loss of traction is not needed for ATB's to operate.

(lets hold very loosely, for a paragraph or two yet to come, whether differing rotational speeds across an ATB (e.g. cornering) isn't any different to a slipping wheel - from the ATB's perspective)

Originally Posted by Slunnie

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,

Errrm... you might be reading something a bit more than intended into my assertion that the ATB is pre-emptive, i.e. it is already set to resist differentiation even while traveling in a straight line.

Am happy to agree with you that while traveling in a straight line, where a 50/50 torque split is naturally in play whether there is an ATB or open diff present - no torque "biassing" is happening at that point.

There is another situation where there is near enough to zero torque biassing happening with an ATB - thats when a wheel is lifted, or when cross axled. (ignoring small amounts of preload) essentially there is no torque torque to bias so no torque biassing in play.

So no argument from me about whether an ATB is doing any biassing when there is no torque to bias, or when the cross axle loading is 50/50.

What i am trying to explain (the preemptive thing) is that with an ATB in play: At any time there is load on the driveline, including when traveling in a straight line with a nice 50/50 torque split, the ATB will be predisposed to resist any differentiation.

(Recall the image of the strap on on the pin with a bit of load on it... can't twist the pin, can't pull it out....)

Call it "onroad situational realtime dynamic preloading (OSRD of the ATB" if you want, no need to call it "biassing".

Further - I am positing that when the likes of Torsen, in the quote I think you have written is "incredibly correct" where they write "– without requiring a loss of traction to operate.", are saying the same thing.

Originally Posted by rick130

Ashcroft's ATB has more inherent pre load and a 'better' bias ratio than the TruTrac, not sure re the Quaife.

The data I have seen in the past for Bias ratio if I recall correctly is:

Trutrac 3.5:1
Ashcroft 3:1

I think I have read perhaps in Ashcrofts information something that would lead you (or rather me!) to think the Trutrac is 2:1, but thats not actually the case, it is actually more positive than the Ashcroft.

Having read on the torsen website that they can have varying degrees of bias with power on and power off(they list the specs as drive/coast using the term TBR).
I'm curious what the Ashcroft bias for both drive/coast is .. or if it's the same.

eg. the Torsen Dana 44 T-2R has a TBR of 4:1/3:1 drive/coast, whereas the same specs for non R version are listed as 2.1/2.3 .. which I assume is 2.1:1/2.3:1

Good e.g. of being able to get the power down with Truetracs.

Range Rover V8 **Eaton No-spin/truetrac Lockers-38.5/11.5/16** - YouTube

Cheers

Originally Posted by Slunnie

The data I have seen in the past for Bias ratio if I recall correctly is:

Trutrac 3.5:1
Ashcroft 3:1

I think I have read perhaps in Ashcrofts information something that would lead you (or rather me!) to think the Trutrac is 2:1, but thats not actually the case, it is actually more positive than the Ashcroft.

Ta, I thought it was the other way around too.

Just gone back through some old posts hoping Ian and Dave divulged bias ratios but alas......