outbackjoe

a camping trip of ridiculous proportions

Diff Locker vs Traction Control

Last Updated 17/10/2016

Diff lockers and traction control are traction aids that help send torque to the wheels with the most traction. They are a massive benefit when offroading on steep and uneven terrain. But which is better?

Traction Control

Traction control utilizes:

  • wheel speed sensors on each wheel
  • brake actuators for each set of brakes
  • something to provide the energy to activate the brakes (provide hydraulic pressure)
  • electronic controller (a computer processor) to interpret the sensors and control the actuators

Traction control applies the brakes to the wheels that have the least traction. This transfers torque to the wheel with more traction.

Diff Locker

A diff locker mechanically locks together the left and right drive shafts of an axle. The left and right wheels always rotate at the same speed when a diff locker is engaged. This forces whichever wheel that has more traction to take more load and prevents the wheel with less traction from spinning freely. Diff lockers can be selectable (turned on or off by the user) or automatic. I have a selectable diff locker and this article relates to this type of diff locker when discussing actuation.

arb rear diff locker switches

Diff locker selector switches on my Hilux

arb air locker entry into diff

Rear diff of my Hilux showing the air line feeding the diff locker actuator.

Which is Simpler

Traction control is an active system. It takes inputs from sensors, interprets the data from the sensors through the software running in the electronic controller, and sets outputs that activate the actuators. It does this continuously in real time as traction conditions change at each wheel, constantly interpreting the data at each moment in time and deciding the required state of the outputs. It takes a lot of effort to actively control something in this manner. It’s a sophisticated control system.

A diff locker is a passive system. Once it is locked, any wheel with more traction will immediately get more torque as the load naturally distributes across the axle. There is no sensing or interpretation of data. The are no actuators to control. The torque is distributed perfectly according to the traction at each wheel due to the physics of the mechanical arrangement.

Diff locker is simpler. It’s passive. There is no intelligence to the system. It relies on the physics of how loads propagate through rotating wheels to perfectly distribute the torque.

Which is Faster

Traction control is reactive. It requires loss of traction to be detected and then brake actuators to be set. This needs to be interpreted from the data coming from the sensors and therefore takes time to process. The actuators rely on physically opening and closing of switches and valves which also takes time. There needs to be some safety margin to ensure noise from the sensors and inaccuracies in the software model do not accidentally trigger the traction control to be activated when it shouldn’t have. This makes the system even slower.

Diff lockers distribute torque immediately as a result of the traction available at each wheel. It is inherently very fast. There is practically no delay. Load from the wheel with more traction immediately transfers through the axle and more torque is the result.

Which is More Accurate

When a wheel loses traction in a traction control system this does not indicate how much traction is available at the other wheel. How hard should the system apply the brakes? Only after the brake actuators are activated and the results are measured does the processor know whether too much or too little braking was applied, by checking the relative speeds between the two wheels when the brakes were applied. This system may initially not brake hard enough and under utilise the wheel with more traction. In this case the vehicle does not advance as well as it could have and loses some momentum. The system may brake too much and under utilise the wheel that had less traction, stopping it from spinning. Although having less traction, that wheel can still contribute to the motive force of the vehicle. Again the vehicle does not advance as well as it could have and loses some momentum.

What if one wheel has massive traction available and the other wheel has completely no traction? In this case the actuators on the traction control system may saturate (reach the limit of their braking capability). The wheel with massive traction might never receive sufficient torque and the vehicle is stuck.

A diff locker will perfectly distribute torque at all times. It happens instantaneously as a result of forcing each wheel to move at the same speed. No matter what the traction distribution is, a diff locker will always distribute torque with great accuracy. If one wheel has massive traction then that wheel will immediately receive massive torque simply by ensuring it rotates. The available traction will transfer load to the axle and the result is massive torque.

Which is Smoother

For traction control to activate it requires a loss of traction. Once this is detected, the actuators are activated and torque is sent to wheel with more traction. This means a momentary loss of forward drive must occur for traction control to activate. Then a sudden burst of forward drive occurs when the traction control activates. Then the actuator releases and the process repeats. This is particularly a problem in low traction conditions where all wheels rapidly lose and regain traction. The traction control system goes berserk, violently shuddering for extended periods.

Diff lockers are perfectly smooth. No loss of traction is required. No sudden pulse of forward drive occurs. When a wheel has more traction it will load up the axle and receive more torque. When a wheel has less traction it will unload the axle and receive less torque. It occurs seamlessly and instantaneously.

Which Allows More Stability / Better Control

Traction control may or may not activate depending on relative wheel speeds and throttle input. It may activate but not with sufficient force. You cannot predict what the traction control will do. You may be attempting to advance up an obstacle expecting the vehicle to effortlessly clear it but the traction control does not provide enough torque. To combat this more throttle is required to generate more wheel spin and more torque transfer. Then once the obstacle is cleared you need to rapidly reduce throttle to avoid going too fast and hurling the vehicle into a heavy impact further down the track. The result is unpredictable and yields large variations in vehicle speed.

Another source of variability in traction control performance is loss of the accumulated energy that provides the hydraulic force to the brakes. When traction control activates it depletes the accumulator that stores the energy to activate the brakes. The traction control system will not operate adequately if the accumulator is not given time to regenerate.

With diff lockers all wheels always rotate. This yields very predictable vehicle performance and extremely stable vehicle speed. There is no requirement to adjust throttle. You can chug along slowly, safety and smoothly at a constant speed.

Which is More Efficient

Traction control applies the brakes. This is wasting energy. Sometimes the energy wasted is significant enough to noticeably feel the vehicle is being sapped of power, particularly in low traction environments when wheels rapidly lose and regain traction with the system effectively braking all four wheels simultaneously once you take an average of the constantly pulsating brakes.

Diff lockers waste no energy. All energy provided by the engine is transferred to the wheels and distributed perfectly.

Which is More Reliable

Passive systems are usually more reliable than active systems. There’s more points of failure in an active system. For a traction control system there’s many sensors and actuators, there’s the electronic controller, the accumulator and there’s all the wiring and brake lines in between. A failure at any of these points will render the system inoperable. I have heard about wheel speed sensors and associated wiring being damaged in offroad situations.

For diff lockers there is a single, slow moving, strong, reliable actuator that locks it in. Once locked it almost cannot fail unless there’s a major mechanical failure within the differential. There is still the potential for the actuator to fail but it is a single point of failure. There are no sensors, processors or other actuators.

Which Causes More Wear

Immediately we know that, when activated, traction control wears out the brakes. It also wears out the switches and valves that operate it. These switch rapidly during operation and so can quickly accumulate wear due to huge number of operations. Not only do the brakes and actuators wear out, but the vehicle’s drivetrain also suffers. The sudden and rapid application of the brakes presents as a shock load to the drive train. In isolation this shock load may not be significant but over thousands of operations it may accumulate to significant wear and an eventual failure.

I’ve done a few defensive driving courses over the years and part of the course usually involves hard braking and manoeuvring on a skid pan. I recall on one occasion an instructor explaining that the CV joints on the vehicles used in the courses suffer regular failures due to shuddering loads caused by the ABS and traction control systems. The wear caused by these systems is real and will contribute to a failure if activated often enough.

Diff lockers do not cause shock loads. The torque transfer is smooth and continuous at all times as governed by the traction available to each wheel. Of course shock loads can still occur if the driver applies excessive throttle when a wheel leaves the ground or bounces off an obstacle. When returning to the ground the wheel will experience a severe shock load. Repeated events can cause failure, particularly on the front CVs of a vehicle fitted with front diff lockers and even more so if the vehicle as been lifted. Traction control systems equally suffer from this type of abuse.

Which is More Automatic

Wouldn’t it be great if you could get a robot to drive your four wheel drive on these difficult trails and you could sit at home on your couch in perfect comfort and watch a video recording of the trip that the robot posts onto facebook for you? A fully automated car. Actually no. That would be crap.

Traction control happens automatically. There is no driver intervention required. It is the more modern, fancy, automated option. Like most modern gadgets that creep into vehicles, to me it’s more of a con to try to keep you trapped in the consumer cycle of buying new cars rather than any real enhancements that make you happier.

With diff lockers you need to decide when you want to use them. It’s part of the experience of controlling the vehicle. You need to turn them on when approaching a tricky section of track. You need to remember to turn them off once your’re on a smooth, high traction surface. You also need to turn a front diff locker off when negotiating sharp turns since an engaged front diff locker makes it difficult to steer.

For me, automating something I enjoy doing and that is by no means arduous to do myself, is not an advantage. Some people might like automatic features. In any case this is not a significant performance measure. Either way it’s pretty damn easy.

Which is Easier to Implement in a Modern Vehicle

Modern vehicles are bulging with sensors and actuators and electronic controllers. So traction control capability is usually already there due to the requirements of other systems. Any additional electronics are cheap. So it’s very easy for modern vehicles to have traction control.

Diff lockers requires an extra actuator and modification to the differential which no other system would share. It’s dedicated. This means more effort and cost is involved in having a diff locker.

What Do Vehicle Manufacturers Think?

Practically every current four wheel drive vehicle has traction control. Modern implementations are fast and accurate and offer good offroad performance. However some new vehicles with traction control, including the new Toyota Hilux, come with a factory fitted rear diff locker. The original manufacturers understand the advantages of a diff locker relative to traction control.

Conclusion

Here is a video demonstrating the performance difference between traction control and diff lockers. The first vehicle is my Hilux with a rear diff locker. It makes it through smoothly and easily whilst the Landrover hesitates due to traction control, rolls back and gets a nice bit of panel damage on the right rear. To add salt to the wounds it’s unable to drive out on its own and must be pulled out by the Hilux.

Note that the Hilux only has a rear diff locker whilst the Landrover has 4 wheel traction control. The one diff locker is so awesome that it can immediately and smoothly send massive torque to the one back wheel that had the traction. Imagine what combined front and rear diff lockers can do!

Is traction control another crappy electronic gizmo that unnecessarily complicates our lives whilst performing worse than the original mechanical method? In my opinion – YES. Traction control performs worse in every performance measure except for ease of implementation. Give me a diff locker any day. I’m a simple man with simple tastes!

This doesn’t mean, if your vehicle already has traction control, that you should get a diff locker. Traction control is pretty good and is more than adequate for most applications. The point of this article is not to instruct people to get diff lockers. Mainly it explains the operation of diff lockers and traction control. Additionally this article deals with consumer culture. Maybe we don’t need complicated and expensive cars. Maybe we don’t need complicated and expensive lifestyles. Consider what you’re trying to achieve before opting for the fancy, technologically advanced, complicated, expensive solution.

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see also

Design Compromise

Diff Locker Front or Rear?

Do You Need a Suspension Lift?

How to Drive on Sand

How Failure Works

Design Guide for 12V Systems – Dual Batteries, Solar Panels and Inverters

How to Catch Barramundi

XXXX Gold – The Great Mystery of the Top End

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28 thoughts on “Diff Locker vs Traction Control

  1. Thank you so much you have saved me a lot of money I was convinced by my deisel mechanic to chip $1200 plus exhaust 1300 I thought the powe for towing Kimberley Karavan off-road might be worthwhile they were saying I would go to about 170 nm on my my13 exceed deisel which has by the way rear diff lock .i almost traded to a discovery for the suspension but got talked out of it for reliability .
    I was thinking that driving on high speed at lower centre of gravity might be safer . Wish ther was an after market option !
    Regards John

  2. Hi, this is a great site! However, if you did that test again with your Hilux and a Discovery 3, on more difficult tracks, I suspect it would be the latter pulling out the former! The Discovery you showed as an example has a very crude form of TC and no ability to lock the centre diff (without modification) – I know, I have one! The Discovery 3 has an excellent form of TC and can do ridiculously difficult fire trails on highway tyres with minimal tyre slip. Cheers

    • Hey feraldisco cheers for your feedback. The video is not a test, it’s an example that demonstrates the science of this article.

      I am sure traction control has improved. Can you explain how the new disco would outperform a diff locked vehicle given my explanation in the article?

  3. Your explanation seems theoretically sound, but I don’t think it fully accounts for the sophistication of modern suspension and traction control systems. I have personally seen a Disco 3 on highway tyres running highway pressures do ridiculous tracks in the Vic high country with virtually no tyre slip. Dial up some youtube vids of modern landrovers and you’ll see what I mean. The wheel articulation and TC means there’s always at least one tyre at each end that has good traction and the reaction to any slip is super fast, unlike old TC systems that seem to require you to accelerate harder to get the TC working and to give you momentum. The new systems are very controlled and smooth so reduced wear on componentry, tyres and tracks. LR know a thing or two about wheel articulation…a vehicle can have diff locks, but if the wheel articulation is poor, it will still struggle on some tracks.

    • Hi feraldisco thanks for explaining that new traction control is better than old traction control and that articulation is useful when offroading. Unfortunately that has nothing to do with traction control vs diff locker. You are trying to defend the landrover as being a capable offroader, which I agree with, but that’s completely irrelevant in relation to this article. All other things being equal, diff locker will outperform traction control.

      My old suzuki sierra, worth less than the tyres on a new landrover, would outperform anything. You don’t need a vehicle loaded with thousands of sensors and actuators and several million lines of computer code to have outstanding offroad performance. Actually, in this case, all other things equal (including suspension articulation), the sensors and actuators and several million lines of computer code perform worse whilst simultaneously adding complexity, expense, increased wear and more points of failure. I’ve heard some stories of new landrovers having some whacky problems with the electronics. This can’t be avoided when you load up so many points of failure. Fancy gizmos are not the right solution for reliable, capable offroading in remote areas. It can be done better and more economically without. That’s why landrover’s use for this application has declined over the last 30 years or so. Landrover is a luxury wagon loaded with gizmos and gadgets. The gizmos and gadgets are for the sophisticated middle class consumer suffering from status anxiety, not for improved off road performance. You can still have great offroad performance with all these gozmos as proven by landrover. Doesn’t mean you need it. Hopefully this article provokes some thought on a vehicle’s intended application vs technology. Sometimes less is more.

  4. I’m not arguing about the benefits of simplicity when it comes to vehicles for remote travel. However, it will become increasingly difficult to obtain simple vehicles and most of us like a bit more in the way of creature comforts than some of the old school vehicles provide – most people spend the minority of their time doing hardcore offroading, so commuting and touring functionality is important (it’s not about ‘status anxiety’). Many of the old school 6-cyl TD vehicles also use 50% more fuel than modern TDs, although I accept that the 4-cyl Hiluxes get ok economy.
    These things can only be proven in a real-world test, and the real-world test you used wasn’t really a good guide as it involved completely different vehicles and the one that had the TC had a particularly crap old school version of TC. All I can say is that I’ve seen D3s running highway tyres have less tyre slip than heavily modified old school vehicles with mud terrains. It defies physics. I agree that some of these systems might become a bit unreliable on high km vehicles, but my argument was purely about capability.

    • I think the hilux vs disco example in this article is valid. That part of the track was a very steep incline with a very uneven portion, where one front tyre was completely in the air, one rear tyre had very little weight and one rear tyre had almost all the weight and all the traction. The track was dry and firm, there was plenty of traction available for the tyre with all the weight on it. Both vehicles were going slow enough so that momentum would not carry them through the obstacle. I think the variables were isolated pretty well down to how well the vehicle can get torque to that one wheel which means diff locker or traction control. At that speed the hilux would not have made it up without a diff locker. Instead it made it up easily. The traction control vehicle hesitated and rolled back. The difference between the observed performance is due to diff locker vs traction control. Job done, the example is valid. Any traction control vehicle has to hesitate to a certain degree for it to be activated. There is no way around this. The new one might be better but the example still illustrates the difference.

      Anyway, for a better real world example, check out the prado videos on youtube where two identical vehicles are tested. This article isn’t about presenting examples, I added that in coz it was an interesting video that supported the science. This article would still be relevant with completely no examples. It’s more about explaining why I think diff locker is better, and to get people thinking about whether complexity and gizmos are actually helping them achieve their goals.

      In my opinion the gizmos and “creature comforts” are about status anxiety. They don’t make you happy according to any research conducted about what actually makes people happy. They do make you poorer and less able to experience the things that actually do make you happy. But that’s beyond the scope of this article, lets not argue about that. I might write more about it in the years to come.

      But yes, traction control can still be a capable system off road.

  5. I think we’ll have to agree to disagree about the suitability of the real world example that you show on this site. A diff lock is a diff lock. The same cannot be said about TC where there is huge variability in the performance of different systems. I have a D2 and I can assure you they are no match offroad with a D3. If you had used a D3 in your video, the outcome would have been very different.

    • Think about the principle that the example demonstrates rather than the particulars of whether car A or B would have made it. This article is valid with no examples. The example is just to help illustrate the science. Maybe the D3 would have made it up that obstacle but what about a slightly steeper one whilst going even slower? If it made it up that one then what about one that is a bit steeper still, whilst going even slower again? Eventually, with all other things equal, the traction control fails to advance whilst the diff locker does advance. The video demonstrates why. It’s to help explain the principle not to represent the performance of every vehicle with traction control.

  6. Hi Joe – something strange happening in your comments postings – what I see above is missing the first few lines of what I see in my email. I agree that TC, by it’s very nature, must detect some slip before it works which must result in some cutting of power/braking to some wheels, theoretically affecting forward momentum. The thing is that with the best modern TC systems, this is all but imperceptible on the track. If you’ve got time, dial up some youtube vids of D3s. It’s kinda ridiculous what they can do up super steep hills at super low speeds. In terms of capability, I would doubt there would be too many gazetted tracks in Aust that would stop a D3, and if they did, it would probably be more due to ground clearance than TC issues. So for 95% of 4WDers, unless you’re going in extreme offroad comps or deliberately looking for ‘trouble’, something like a D3 is going to exceed your offroad performance requirements, so you don’t need to worry too much about a theoretical diff lock vs TC control debate in terms of capability. Long-term reliability and serviceability is a different story of course…although modern LRs are much more reliable than the old ones…it’s just that the old ones were easier to fix in the bush when they inevitably broke down!

    • Yeah agreed, with hundreds of sensors and actuators and a few million lines of computer code and a control system sophisticated enough to run the space shuttle, the new landrover can now almost match the capability of two actuators from 50 years ago. But the theoretical performance advantages of diff lockers are still there along with all the other advantages of less complexity, more reliability, less wear, better efficiency, etc.

      So your philosophy is, if the super expensive complicated solution is good enough 95% of the time, then don’t worry about the simpler more practical more reliable solution? What sort of logic is that?

      What I’m saying is to think about what you are trying to achieve. Maybe you don’t need to spend over 100k on a fancy new landrover with the most advanced traction control in the world.

  7. I don’t know a lot about the diff locks but have mates with them and they say they are good, but traction control is better then nothing, a mate and I went up scrub though a lot of muddy stretches, now he owns a Colorado with no diff locks or traction control, but he had new mud tyres, I have the Triton that comes standard with traction control and had near bald A/T tyres, now he needed to engage 4wd in some place where I could cruise through in 2wd, guess what I’m saying is although Id like to have diff locks, I find traction control does an absolute great job in the mud and surprised me how well it worked.

  8. I think so Diff Locker beats Traction control but, if we would consider that example comparison video we will mistake regarding TC just like mentioned by “feraldisco”. Because there is no need to be expert, so that got it center lock not active on D2 in video. Without there is any ulterior motive, we have to be carefully when giving example, otherwise there would be occur that thought some hidden advertising. Disclaimer “I don’t think so”

    By the way I have disco 3 and much more video when off roading so that compare with TC and Lockers.

    Regards.

  9. Hey Joe

    Great Video and very helpful.

    I am more into dessert sand dunes offloading driving, nothing crazing I just enjoy cursing every now and then.

    I own a ford expedition ( I know it is a heavy vehicle!). What I normally do to avoid getting stuck is the following:

    1. Reduce Air Pressure to 18.
    2. Turn on the H4 on my 4WD dial.
    3. Drive with a steady speed on THIRD gear.

    The car does have a traction control that get disconnected Automatically on Low Gear (L4). Do you recommend that I turn it off also on H4 for the reasons you have stated above ( mainly wear and tear)?

    Thanks and Happy New Year

    • Yeah in sand the constant small amount of slippage can make the traction control shudder the whole time. It ain’t good. If that’s happening I’d turn it off. On firmer dune ascents over uneven terrain it may help keeping it on. I discuss it a little on the how to drive on sand article if you want more info.

  10. Excellent reading. The most information I have ever seen.
    There is one thing still puzzling me though after tons of information! Is is good to turn on Traction control if stuck in deep sand, all four tyres spinning? Or do I need to actually loose traction on some tyres for it to work? I have a Ford FX150 Platinum.
    Thanks, Tina

    • Hey Tina if the reason you are stuck is because the sand is very deep and soft then I don’t think traction control will make much difference since all the wheels have adequate weight. Turn it off to avoid the constant shudder and associated wear. If stuck due to uneven surface then turn it on. In general for sand I’d keep it off otherwise it gets triggered all the time for no benefit. More details are on the how to drive on sand article.

      • Thanks for feedback. Will keep in mind for next outing. Passed on your website to a few friends here also.. Tina

  11. i found this article to be a great read, i don’t believe for 1 second that a car with Diff locks can be out performed by one with just traction control as stated by a previous critic. if people wonder how wheel rutts are created? mostly by vehicles losing traction and digging holes or pitts and almost making some tracks redundant as ground clearance becomes an issue. i own a new Y62 Patrol and can tell you that since i have fitted the Front Locker my car conquers many a beaten up track that i struggled with previous to the Locker installation.

  12. You make out as if a locking diff is more efficient, it isn’t. If one wheel is spinning because it’s off the ground, 50% of the power is being wasted. This wouldn’t happen with traction control.

    • Hey Oliver I’m not sure what you mean. With a locked diff the wheel that is off the ground will receive almost zero torque and almost zero energy. It receives only the energy required to overcome the friction in the bearings etc. Practically nothing. With traction control the torque is always equal on both sides since it’s an open diff. The brakes generate the torque on the lifted wheel by friction and in doing so waste energy.

      • A locked diff distributes equal power to every wheel regardless of traction etc, so the free wheel would be spinning, thus waisting energy/power. With traction control, the braked wheel would be receiving zero energy, since it’s an open diff, all the power would be sent to the non-braked wheel. Perhaps you should do a little more research on how open and locked differentials actually work.

      • Woa there you’re way off dude. You should read my first response, and do some research, and maybe learn some basic physics.

  13. Feel free to dismiss that actually, I’m being brain-dead

  14. Out back Joe,

    You have made some interesting comments and remarks… Can I ask you what your qualifications and experience is?

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