Thread: Locker vs LSD in the front.

(Written under the influence of a few drinks with a meal - apologies in advance for errors, omissions, and any flights of fancy.)

Originally Posted by rovernutter

I do not follow. For a quaife or tru-track to put power to the wheel with traction, the other wheel has to actually spin first.

Not so. Reference my post a little up above here....

Maybe if I liven it up a bit with an example of just one scenario:
You are driving in a straight line. No differentiation happening, all wheels turning the same speed. The ATB fitted is actually already resistant to any possible call for differentiation:
- if the applied throttle was light, very little torque in play, the resistance to differentiation, were it required, before any differentiation even started, would be light.
- if the throttle was down hard, lots of torque in play, the resistance to differentiation, were it required, before any differentiation even started, would already be heavy.

This illustrates how it is the torque in play that causes the resistance to differentiation. The torque being applied to the driveline makes the helical gears "bind up" in their pockets causing resistance to any relative difference in movement either side of the ATB. How much resistance is dependant on how much torque is in play. Coasting down a hill may mean little torque is in play, hardly any "weight" on the driveline. Driving hard up a steep hill - the opposite.

When a wheel is spinning freely in the air there is basically no "weight" on the driveline, little to no torque in play, hardly any force on the helical gears so no binding up and no resistance to differentiation so no drive to that other wheel on the ground.

Add a bit of resistance to the freespinning wheel (i.e. ATC applying brakes for example) and now there IS some "weight" on the drivetrain...torque in play, helical gears binding up and providing some resistance to differentiation - giving that wheel on the ground some much needed drive.

Originally Posted by rovernutter

So one wheel has to be spinning faster than the other for the biasing to the other wheel to take place. This is where I would think that traction control would hinder its operation.
Still not convinced that traction control would allow enough wheel spin to get it to work fully though. But I have been wrong before.

Think about how traction control works with plain open diffs. When a wheel spins it is braked momentarily(repeatedly) and drive goes to the other wheel proportionately.

Traction control is complementary to an ATB in that it does the left foot braking for you (and only brakes the wheel that needs it). Simple as.

Originally Posted by tact

Think about how traction control works with plain open diffs. When a wheel spins it is braked momentarily(repeatedly) and drive goes to the other wheel proportionately.

Traction control is complementary to an ATB in that it does the left foot braking for you (and only brakes the wheel that needs it). Simple as.

From what you are saying, it appears that it would be difficult to get anywhere with a Truetrac if you did not have traction control. You would have to continually use the brakes in situations of low traction, which is when you need it.

Sounds too complicated. Might do some more reading on it though.

I think you have answered the question as to whether do with a diff lock or something like a Truetrac.

Originally Posted by rovernutter

From what you are saying, it appears that it would be difficult to get anywhere with a Truetrac if you did not have traction control. You would have to continually use the brakes in situations of low traction, which is when you need it.
... .....
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There is a difference between low traction and no traction.

In most situations if the wheel is on the ground, it will have some traction and usually enough to transfer torque through the ATB to the other wheel.

You obviously don't need TC for an ATB to work.

I've got one, it works.

I've also got an ARB air locker in the back diff which works when it's not leaking.

The ATB works just as well off-road until you lift a wheel.

The ATB works very impressively on-road.

It doesn't require LSD oil.

It doesn't make steering difficult or dangerous.

TC doesn't really interest me (in a Defender) and I'd buy the ATB again without a second thought. In fact if they made them for the Salisbury I'd put one in the back diff as well. For the type of driving I do it enhances the vehicles performance in 99.9% of situations both on and off road when compared to an open diff, which is what you have 99.9% of the time if you have air lockers fitted.

This is an interesting read on the different types of diffs:
Differentials (Open, LSD and so on)

It actually explains that ATBs are not really suitable, and are not generally used, for 4WDs.

In the case of a truetrac, the torque bias is around 2.5:1. That is, it can supply 2.5 times the torque to the wheel with grip compared to the one without grip. This is why they will not work with a wheel off the ground as 2.5 times nothing is still nothing.

So even if the spinning wheel has some traction, it can only transfer 2.5 times the amount of torque that can be supplied to that wheel to the wheel with better grip. So if the spinning wheel has very little grip, it cannot supply very much power to the other wheel.

This is where the traction control comes in. By apply the brakes to the spinning wheel, it actually increases the amount of torque that can be applied to that wheel and therefore the amount of torque that can be applied to the wheel with grip.

ATBs are obviously designed more for race cars than 4WDs. It sounds like you would be a lot better off with a LSD rather than a ATB. A LSD uses the the spinning of the wheel to direct power to the wheel with grip. The more spin the more power transferred. It does not require any load to be on the spinning wheel like the ATB requires.

But I will stick with my lockers. I only have to worry about a switch and not about loads on wheels, etc.

It is all interesting stuff. It was worth having a look at.

This is a quote from another site:
"All gear ATBs (including Torsen?, Truetrac?, Quaife?, Peloquin, OBX, etc.) work in basically the same manner: they divide the drive torque between the two axles, applying drive to each side, up to the available grip of each tire. The amount of drive torque one wheel can get over the other is described as the bias ratio, a measure of the torque split across the axle.

Standard, open differentials have a bias ratio of 1:1. They can only apply as much drive torque as there is available traction at one wheel. When one wheel loses grip, the total available drive is lost as well (at a 1:1 ratio). All your power goes out the slipping wheel - along the path of least resistance.

Torque biasing differentials offer increased bias ratios over open differentials. For example, if a diff has a bias ratio of 2.5:1, then it can apply drive torque to the wheel with the most traction (gripping wheel) at 2.5 times the traction limit of the wheel with the least traction (slipping wheel). This is a significant improvement over an open diff?€? most of the time.

The problem is that when one tire has LITTLE or NO grip (zero axle-load), the other wheel gets ZERO DRIVE, because (basic math here): 2.5 x 0 = 0.

Lift a wheel (or substantially unload a wheel) and you get zero axle-load on that side - that means that during the time the wheel is unloaded, the typical ATB diff will NOT power the wheel that’s still on the ground. No matter how high the bias ratio, you get no power to the ground.

During the transition from accel to decel, where you have near zero torque on the axle, even if the wheels are on the ground, the typical ATB diff is unable to begin applying drive torque until AFTER the zero torque condition is over. While this condition is generally short-lived, the fact that most diffs can do nothing during that time means that there will be a delay once the zero torque condition stops - creating a reaction time in the driveline."

Originally Posted by steane

You obviously don't need TC for an ATB to work.

I've got one, it works.

I've also got an ARB air locker in the back diff which works when it's not leaking.

The ATB works just as well off-road until you lift a wheel.

The ATB works very impressively on-road.

It doesn't require LSD oil.

It doesn't make steering difficult or dangerous.

TC doesn't really interest me (in a Defender) and I'd buy the ATB again without a second thought. In fact if they made them for the Salisbury I'd put one in the back diff as well. For the type of driving I do it enhances the vehicles performance in 99.9% of situations both on and off road when compared to an open diff, which is what you have 99.9% of the time if you have air lockers fitted.

Completely agree with all that above. I have ATBs (Ashcroft's) front and rear in my 110. I went that way because my 2013 TDCi did not have traction control, just open diffs, so it needed something and I was not interested in wholesale mods to bring all the driveline up to HD spec.

For sure if your defender is a competition or play vehicle and not a daily driver then selectable lockers might be the better choice.

But for my needs and use as daily driver - I prefer having the ATBs working for me on and off-road, every kilometre I travel, no maintenance needed other than normal diff oil changes. No compressor needed, no headaches with leaking air lines etc.

As for off-road ability - if you can keep all the wheels on the ground, you just choose line and drive the vehicle.

If you throw a wheel up then some left foot braking skills are needed to get/keep moving - unless you have traction control, then you continue to just drive with a little more throttle to compensate for ATC.

The selectable locker alternative will make life easier in those wheel-in-the-air spots. Trade off being your cost to uprate all driveline components to HD and sacrificing the ATB benefits in all other off-road as well as onroad situations.

I do some serious off-road trips into the Malaysian jungles in the company of mates with vehicles that are lifted, run 35" tyres, some with SPOA conversions, most with air lockers. My barge is also my daily driver, largely stock standard, no lifts, just the ATBs and a tune, and til recently was still running the stock 235/85 (<32") AT tyres. (Now has 33" MT).

On the hard off-road trips I often get "how the hell did you get through!?", so far zero occurrence of "oh no, he's stuck AGAIN". Happy.

While it's arguable that full on selectable lockers are essentially a one trick pony: I.e. The wheel in the air scenario (and its equivalents that result in near zero traction on one side of a diff).

And that this scenario is arguably the Achilles heel for ATBs and open diffs.

Gotta quickly add:
- that doesn't mean that vehicles with ATBs or Open diffs immediately come to a steaming shuddering fullstop as soon as any one wheel gets air. Of course not.

- many times when a rear tyre is lifted, both fronts pull you thru - and vice versa.

So it's only the really extreme situations (i.e. not every wheel with air situation) where full lockers are the ONLY game likely to save you from having to break out the winch.