What is an e diff? (Computer controlled limited slip differential) | Auto Expert John Cadogan

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An e-diff is a computer-controlled limited slip differential, activated by a high-speed servo motor. After looking at inputs like the steering wheel position and the cornering load, yaw rate of the body and throttle position, the e-diff distributes drive left and right to maximise traction and increase cornering performance.
The result is more traction, increased yaw rate (less understeer) and you can get on the throttle earlier in the cornering process in extreme driving situations - such as on a racetrack. Earlier throttle application makes the car faster on the next straight and slashes lap time, obviously.
It takes a while to adapt to an e-diff on a track - initially you feel as if you are getting on the gas unreasonably early in the cornering process. When you get used to it, however, you'll see your lap times tumble...

[@Conservator.]

John, I love these kind of technical subjects. Bring them on, please. Can’t wait.

[@jamesplotkin4674]

I agree.

[@highlypolishedturd7947]

Me too. John, you do explain things well. Even better when you're serious, and not trying too hard to be funny.

[@jasoncee666]

Sub to my man at Engineering Explained channel 🙋

[@Conservator.]

Jason C Can’t sub twice (to the other Jason;)

[@Pilski]

AMEN!!!

[@connordunn2532]

Gave a thumbs up just for that definition of weight force vs mass - never heard it worded better.

[@gazzafloss]

Lucky for some of us aged folk to have someone to explain modern car Tech to us John, I'm ok with the old stuff but have definitely slipped behind with this new gubbins. Thank you.

[@highlypolishedturd7947]

Yeah, well said. Listening to jargon and tech babble reminds me that I'm getting old. Now, where did I put my reading glasses...

[@jfv65]

Way back 1995 i owned a Volvo 850. It had a system called TRACS. it used the ABS system to brake the inner wheel whenever traction was lost. It was crude but it sorta worked. I prefer a mechanical torsen diff. It provides seemless lock between 0-100%, whenever it is needed to stop the inner wheel from spinning.

[@DanWallis86]

John. I always love the beer garden and explanations you offer. It’s great to hear you talking about a car you love so much too. Makes me want to test drive an i30N. Keep it up mate.

[@mahcooharper9577]

Far be it for me to blow smoke at you John, but even as a long time viewer/reader it still strikes me as nice to have someone who is immune to the lure of car company junkets and tells it like it is and someone who actually understands how cars and the industry works. I always enjoy the tech videos. And we have an N Fastback in the family (just hit 1500km) and it's fkn awesome. Can't wait for the review.

[@MrAndrew1953]

Datsun used to amaze me with their indepent braking set-ups on their rally 1600s. Thanks for the tutorial prof - always good /grateful to have punters understanding of these complex systems. Thanks for doing that. Amazed you can get an e-diff on a production Hyundai.

[@ultravern]

I tried one of those i30N Fastbacks at my local Hyundai dealer and was very impressed and would have bought it too but I need an auto due to my ruined left knee. I bought a SEAT Leon Cupra instead which has a similar diff. I've never had a front driver before in more than 35 years of driving but, once you get the hang of the diff, it works beautifully. I doubt I could breach the cars limits on a public road here in the UK without winding up in prison. Sorry John, I know it's made by the Devil's own car company but it looks lovely! Great vid, thanks.

[@santillbrezon2161]

All your videos are great john my wife and myself enjoy them all.

[@AutoExpertJC]

Tell her I said she's very tolerant... (Thank you both very much.)

[@macbuff81]

Love learning about these technical matters from an intuitive and comprehensive presentation :)

[@robertsmith5557]

Ditto John. Great tech. That drift was a beauty.

[@MrWilliam.Stewart]

John loves putting his propeller head hat on, his audience loves when John puts his propeller head hat on. Call it a win win wouldn't you say.

[@jimdannock898]

Great article. As a i30N owner for the past 12 months the e-diff is great fun. Powering out of a corner is amazing and it is so well tuned I get no interruption from the electronic traction control (unlike my previous Veloster turbo). Probably having the e-diff set to Sport mode all the time doesn’t contribute to long tyre wear.

[@majestictwelve3709]

Great video JC. My insomnia was really getting out of hand but this cleared it right up

[@TheNortheastAl]

Thanks, John for today’s physics lesson. I enjoy them very much and they help to explain why our cars do what they do. More would be fine with me.

[@lewisg1736]

I very much enjoyed this episode. Perhaps you could offer a talk on the differences in all-wheel drive systems in the future. I do miss your sharp wit that we are used to on many other talks, but this was a pleasant addition. Thanks again.

[@kelstra1997]

John I always enjoy these technical reports and would love to see them appear regularly. You explain the function of the e diff very well but it seems to me that it achieves exactly the same thing as traction control - which most cars have these days anyway.

[@bluecent]

Great explanation. In simple terms I explain it as it “pulling the front wheel drive car through the corner, as opposed to running wide”. The best example is those multi-laned roundabouts where the diff literally pulls the car through the corner. And let’s not forget other manufacturers also have these too.

[@805fpv3]

wow you killed this demonstration! Amazing job sir ! God bless you and keep up the good work :)

[@ByronWWW]

Have a vaq ediff in my cupra, took a long time before I discovered how it worked on public roads because expectation was that it would just understeer off the road - there is a brief moment of doubt before it locks up but the drive you get out of corners is crazy. In the wet in the most aggressive setting, when it looks up it tightens the line so much around small roundabouts you need to wind off the steering lock a bit - can actually feel it tug the front end in.

[@gordonclark7632]

Understanding comes with good explanation. You did that and I learnt something that I never really understood.

[@D800Lover]

John in 'no smut' mode today. My ears thank you.

[@guyandrewsironman]

Best tire pressure for different driving outcomes. Track, country road, city. Pressure changes during performance driving on road tyres. Thanks JC

[@timothycc711]

Thank you John. I already knew this stuff but always fascinated with these topics. I want to add some kind of mechanical limited slip to my F150. Great driving on the track! One suggested topic- continuation: how limited slip help during offroad situations and the various lockers and limited slip diffs available such as torsion setups.

[@rtaylor0361]

Love to here your analysis of the Prelude ATTS

[@johnmajkowski7200]

Thanks for a very understandable explanation of weight versus mass.

[@adriancoyne851]

yes please john,love how you explain how new gadgets on cars work,cheers

[@nemlol]

I wouldn't mind seeing you review higher end cars. And keep pumping it out, loving the channel.

[@bobfrombrisbane1831]

Hi John, I found this video informative and easy to understand. Thanks. 🚗

[@AutoExpertJC]

Thank you Bob.

[@joshh2645]

Great video! Keen to watch more videos like this.

[@aussiesam01]

Hi John, pretty good description of what a diff does, thanks, but seemed to stop short of explaining the electronic/mechanical operation of the e-diff itself while working its magic. Would you kindly consider adding a description of the electro-mechanical operation of the e-diff and how this might differ from a mechanical limited slip diff. Thank you.

[@curtislitchfield1378]

I"m a fan of the visual queue with the blurry "race track turn" :)

[@stevenlee9064]

great explanation of e diff.

[@hudrob1976]

Great video, thanks John. Please produce more content like this, it is great having a reference for concepts to show to others. Could you do one on front and rear swaybars, and their impact on cornering behaviour? :)

[@TwoHemiViewer]

What should have been added in commentary is that the diff has a hydraulic clutch pack actuated to the wheel that has lesser traction to add portions or total traction to the spinning wheel via all the sensors that he did mention .

[@dazzamac70]

John, awesome breakdown of the aspects of the e-diff!!👍

[@johnloncar7785]

Beer hall physics. I like it. You probably should have mentioned that gravity is a type of acceleration. I reckon a few more lightbulbs would have lit up.

[@AutoExpertJC]

I should probably have mentioned to remember to keep breathing as well...

[@missingnola3823]

Love the applied physics; please keep these coming! --John Skinner

[@barrettwbenton]

Terrific. BGP is always fun *and* informative. (And, yeah, I think you're pretty sweet on this Fastback.)

[@Pilski]

Great video! Really love the analogies, description and presentation in general!

[@kiwiryker]

Awesome John ,, This is the best way explained that everyone can understand

[@roddaniels1809]

Great explanation on a complex subject John.

[@sjbiggs01]

Great explanation. Now can you contrast an eDiff with a mechanical limited slip diff? How do they differ in the “inputs” available to each and does one perform better than the other? Thanks.

[@tonykb2193]

Not if you had a quaife LSD. No computers needed, the engineering of it is just right, no clutch packs to wear out like the electronic diff will have.

[@andrew1977au]

Do a video on lowering a car, the effect and effects when it’s done right vs wrong

[@BPantherPink]

Wonderful explanation... JC

[@dkinney1000]

Nice one John, every bit a driver's car by the sound of it and it looks rooolly fast!

[@michaelrussell6661]

The difference between rear wheel, front wheel and all wheel drive in regards to how they get power down and handle. I have a rough knowledge of how they all work, being explained by someone who actually knows what they are on about would be really handy.

[@antone.henderson]

Thanks for another dose of simple to understand enlightenment. Regards Tony Henderson

[@mickdalrymple6425]

Great work John, thank you

[@AutoExpertJC]

Thanks very much Mick.

[@m.v.k4681]

Just one word FANTASTIC!

[@anthonybuffolin185]

Hi John, Keep this kind of stuff coming, well at least for me. Ties in nicely with the car reviews as it really gets into the nitty gritty of certain vehicles and what's you get for your money. If you're looking for a topic what about exhaust system tuning? 101 style and then in-depth for nuts like me. Please and thank you always. Regards Anthony

[@ToyBJ]

Perfectly understandable thanks JC 🤪👍🍺 , basically nothing like the lockers in my Landcruiser then ? Lol 😂

[@L3aRn2Th1nK]

Talk about what is torque split or maybe how the fixed and variable centre diff works and the pros/cons in handling. (WRXs spring to mind)

[@andrewthompsonuk1]

I have to add there is a big difference here from the cars that apply the brakes on the inside wheel with an open diff. Sometimes this DSC function is described as an eDiff by car sales people. But remember applying brakes means lost power and slower exit speed.

[@AutoExpertJC]

And traction control typically intervenes first by reducing engine power.

[@geoffreyveale7715]

I can see that an e diff would be good on a race track to get the best lap time, but surely the computer applying a little braking on the inside front wheel to limit wheel spin would have a similar effect. Applying some braking on the unloaded front wheel should allow the average driver to get around the corner just as safely and would be what you would expect in a car with a good traction/stability control system without the complexity and cost of an e diff.

[@SunRise-ul7ko]

I wish I had an E-diff on my SV6 VF commodore. I quite often spin a rear wheel accelerating around corners in the wet.

[@kadmow]

@@AutoExpertJC: TC kicks in?? No!!

[@michaelstuehrk3396]

Nice work sir, can you refer me to a good quality animation of the e diff in action,or perhaps a cut away view. Thanks

[@davidrusso4750]

Excellent - really enjoyed your discussion and explanation.

[@bondisteve3617]

Loved it....all of it! Many thanks.

[@JohnHeidemann147]

Love the explanation of an e-diff. Can you explain how the Q2 diff in my Alfa 147 GTA achieves the same result mechanically? Fitting that transformed the entire car and tamed the power much as you describe here.

[@ceterisparabus]

I put a quaife q2 style lsd in my Subi, was epic.

[@JohnHeidemann147]

@ChrisHallett83 Excellent video explanation. Thank you! The Q2 totally transformed the GTA. Eliminated torque steer and tamed the power into productive performance. Best money I ever spent.

[@daveg872]

John, bring on the hardware and electronics explanations. Its interesting to know how it works and the affects on the vehicle. You might also share the cost of living with it if there is any special maintenance involved. An example would be the VW GTI DSG transmission. Early examples required an expensive flush every 40K miles here in "Merica" which was a surprise to many. If you're going to dig into something, please explain continuous variable valve timing for intake and exhaust valves.

[@pablostraub]

Great explanation. And surprisingly no foul language 😂

[@AutoExpertJC]

Thank you. It was a major fucking effort though...

[@andyslatter6143]

John, great topic. I am a big fan of front drive small cars and find any LSD ( Limited Slip not Lucy in the Sky) something that totally alters the experience. My conclusions on the current ( not driven 130N) E-diff vs haldex/ torsen vs LSD with clutch pack are that it is very digital vs analogue. That is I much prefer the torsen ( quaife in a little Clio172 specifically) as the engagement is seamless where the digital diffs that I have experienced have not evolved to the point where the application is so gentle. On a track where it is black and white, on or off, it is probably less obvious but on a dirt road or perhaps an underpopulated b-road with low traction it stands out like dogs balls when the E-diff engages and can have additional consequences. Big initial under-steer. I understand that the process control needs an initial feedback to keep the whole thing in check but I think Bosch or whomever are not there yet.

[@aeroloco4352]

Hi Jon loved the vids. Please consider adding visual aids, charts etc in your explanation in your future videos especially when you mention angles and down forces etc.

[@dillonvossen1144]

love the tech details JC!

[@byronnightingale5550]

I like a good tech talk, and also a good physics discussion. Would you entertain the idea of a comparison between the isochoric process and isobaric process. The isochoric process takes place in the petrol engine, where the isobaric process takes place in the diesel engine. I wouldn't mind your take on these processes. Real McCoy physics this is.

[@sjm.photos]

Had one of these as a courtesy car it wasnt bad at all. Great explanation

[@E82N55]

I thought your explanation of weight transfer and tire friction was great, but I think you missed a big point about how ediffs work when slip is sensed, which is by using the ABS system to brake the slipping wheel thus sending power to the other wheel through the open diff. The cons to this system is that the brakes can get much hotter than using a mechanical LSD

[@melvinshelton8448]

Hi John, You instructed your audience to let you know if we want you not to discuss/translate/simplify the very nuts (so to speak) of your presentation. Please just continue teaching this way, thank you very much. You got it in one. Please refrain from fixing it. Ta!

[@aussietaipan8700]

Good tech subject JC.

[@AutoExpertJC]

Thank you, deadly snake...

[@ridingwithpat]

Thanks John, more of these please. Maybe one on why my 2004 Prius uses about half the fuel my 1990 Camry wagon used for the exact same across the suburbs 50 minute commute. And another about why the Prius can still achieve that result with 320,000km on the clock on the original battery. Maybe a show about how over the life of a Prius it can save 12,000 litres of fuel compared to a similar size petrol only engine car. Yeah, I know you won't. I do seriously love your work. Have you seen Book Of Mormon? I think you'd love it. I saw it last night.

[@regsparkes6507]

Got it,..the principle of the E-diff,..now I wish I could experience this 'feeling' and drive like I stole one!

[@freefall0483]

Very nice explanation. Can you do a vid explaining the difference between an e-diff and torque vectoring.

[@rangerover06sc]

The big difference between an actual, mechanical torque vectoring and e diff is that an e diff will lock with a variable amount of torque to try and get the wheels to spin at the same speed. A torque vectoring diff will selectively engage or disengage clutch packs so that certain wheels spin faster. So in the scenario mentioned in the video, an e-diff can shift more torque to the wheel on the left( that has all the traction), and greatly limit how much faster the wheel on the right is spinning ei slipping. A torque vectoring differential can slow the wheel on the right and make the wheel on the left (that has all the traction) spin faster and get more torque.

[@standupmoto]

Great explanation of the E diff and put into “don’t have to be a rocket scientist “ to understand terms. I know your not into 4WD off-roading clips climbing mountains etc but would like your take on the new Suzuki Sierra or Jimmy or whatever it’s called nowadays. I have subjected myself to three of these got to be a mother to love them little gems in the late seventies & mid eighties (1x2 stroke & 2 new 4 strokes) before kids houses and station wagons and now reaching mid life crisis point am looking for a toy and remember fondly my Suzi days. I was never really in a hurry to get anywhere (just as well) but I was also never let down no matter what or where I put them and wondered if they are still as capable and reliable as they used to be now they are fitted with all the latest tec?

[@banjodevon-willis5487]

I feel like the beer garden physics definitely needs beer. Other than that it’s tip top stuff 👌🏼

[@AutoExpertJC]

Thank you very much. Everything gets better with beer, of course.

[@wafive]

John could you please go further into the mechanical aspect of how the diff actually sends the power to the wheels, is it a clutch pack or some other jiggery pokery

[@nickbouvy8851]

So by the sounds of it the diff actually vectors torque to the outside wheel and it’s not just a case of the inside brake being applied to load it up. Should work very well and get rid of the biggest problem with front wheel drive. The boys would still miss power oversteer but it should be very quick around a track.

[@mcmoose64]

Well explained John. More like this thanks!

[@robertlawrence2748]

Hi, I would love to know how this E diff compares to the passive diff in the Civic Type R, when driven with some vigor :) Cheers!

[@rdvil]

Definitely need to dig a little deeper in to the subject John, this left at least me a little hazy on the difference between brake traction control system and e-diff. Is there a computer controlled clutch pack inside the diff like in early 90's Benzes or does it use the normal brakes to achieve the same effect like every other modern car, or something fancy like a servo rotating a planet carrier in the one or the other direction like in a Volt/Ampera? And what's the benefit v. torsen such as a Quaife diff?

[@MiniLuv-1984]

Like beer garden physics John. I imagine the "e-diff" is an open diff with braking applied to transfer torque - like traction control, just faster. Imagine now bypassing this whole goofy approach by driving each wheel independently - like you could in an EV with a motor per wheel. As far as I know, only Rivian are doing this on their 4WD. Can't wait for the future!

[@AutoExpertJC]

Not really. It's a clutch pack, not a single-wheel ABS activation.

[@MiniLuv-1984]

@@AutoExpertJC Thanks John, yeah, I looked it up after I opened my big mouth.

[@jeremywatts2768]

Great video, but I still dont get how it actually physically controls the axles. It looks to me that the unit is an add-on bolted to _one_ side of the transmission but I can't get anyone to explain what its physically controlling. It looks like a VW Haldex unit that operates like brake clamping to force an open LSD to bias the drive forces. How is it controlling both sides? Does this have to work in conjunction with the brake vectoring system to work? I wish somebody could show an entire unit of the transmission with and without this unit installed so I can understand what is different.

[@FlaviaPitariu]

I loved the episode. I'd like to learn more about Mitsubishi active yaw that is present in the Mitsubishi Evo

[@frankbarbara2507]

Thanks for all that info, I didn't understand all of it,, but that's OK, cheers 🥂 🥂 🥂 🥂

[@livenloud6697]

Is that you driving john ... wow.. 😎

[@peebow1000]

We want more physics, thanks. Talking about differentials, there's various types for various applications yes? As in diff systems that can transfer 100% torque to individual wheels etc..?

[@andrewharms2460]

John would you please do an update regarding the sales stop of hybrid Toyota cars .

[@tomnewham1269]

Hi John, I take it the e diff would also limit torque steer as well which was a real dislike for me when I drove an Audi once.

[@masterDarcy13]

Hi John .. could you explain the real difference between a front and rear wheel drive car . Is one better than the other ?

[@DavidPruitt]

Point of contention, an object on the ISS doesn't weigh "zero". The object still has weight and is falling towards the center of the Earth. The reason that it doesn't hit the Earth is that the object is moving fast enough that it's trajectory happens to end up being an ellipsoid that never intersects the Earth. Taking your brick, it weighs say 1 kilo on the surface of the Earth. If you let it go it goes straight down. If you throw horizontally it follows a curve. In both cases the weight is the same, 1 kilo. If you kept throwing it harder and harder it would end up farther and farther along the ground. In each case its still 1 kilo. If you threw it hard enough it would end up following the curvature of the Earth, essentially falling around the Earth. And its still one kilo. Clearly that won't happen because of air resistance slowing the object down. By sticking the ISS at an altitude of 200ish km there is minimal resistance from the atmosphere. Therefore it still has weight, but due to its horizontal speed it falls around the Earth rather than into the Earth. The reason that objects on the ISS appear to be "weightless" is that all the objects are falling around the Earth at the same rate. If you let go of a brick the Earth holds you still while there's nothing to stop the brick, until it hits the ground. In remembrance of the fact that we managed to get a man to the moon and back 50 years ago and where clearly ahead in some ways at that time. The moon where a 10 kilo object is a 10 kilo object and a 22 pound object as weighed on Earth would weigh 3.6 pounds.

[@declan1327]

Hang on...don't you mean that the MASS always stays the same? I thought that how much a thing WEIGHS, was due to to it's proximity to another mass. you know...that gravity stuff.

[@petesmimob]

Dear John, Thats brilliantly explained, thank you. So what is the difference between an E diff and a Limited slip diff. Best regards Pete

[@aussiebloke609]

I'm guessing this system is a little different to Hyundai's TVC (Torque Vectoring Control), but it sounds like a similar concept. As I understand it, TVC uses the individual front brakes to slow the inside wheel when it detects a loss of traction, rather than just cutting engine power, and slowing that inside wheel will transfer the torque to the outside wheel instead so long as power is still being applied. As best I can tell, this E-Diff system adjusts the torque vectoring inside the diff itself, rather than using the brakes - which is probably better in terms of a track day, as it will reduce brake wear and heat, and likely lets the system be more proactive in terms of adjusting torque output as you drive. Same idea, but a different method of implementation. Or have I misunderstood how this works? Let me know what I've missed/screwed up. :-)

[@charliestuart3657]

Just fascinating, nicely done. Do you like motorcycles also John?

[@andrewmoorhouse687]

Very interesting and informative John. You won’t hear any objections from me if you cover more modern car tech in future episodes. There’s kind of a negative being a positive! The only caveat with limited slip differentials, I understand, is if you are at maximum sideways grip on the driving tyres of your car, the transfer of power to the outside loaded tyre can overload the grip on that tyre, resulting in a sudden loss of grip. This can lead to a spin in a rear drive and especially rear weight biased car: mid-engined or rear-engined sports cars are particularly prone to this, especially if it’s purely a mechanical diff. Speaking from scary and costly experience here. Front-drive cars are less likely to suffer this, I suspect, and even if they do it’s just going to understeer on you, which is probably easier to control for most.

[@iansalgado8710]

Love it !!

[@redhaze8080]

that thing looked so well balanced at Targa Tas

[@gavinlee9928]

Great, thanks John. You explained the e-diff's effect on handling. I would like to see how the e-diff works. I.e. dismantled on a bench in a workshop?

[@AutoExpertJC]

It's just a limited slip diff that's actuated by a high-speed servo motor. Looking at the parts hardly ever tells you much about how it works. It's a motor and a clutch pack attached to a differential.

[@azizbass]

Hi John great explanation as usual maybe it might help to have some videos of you actually demonstrating this and talking us through it just an idea thank you .

[@aaronbryan5095]

Have you driven late model Lancer Evolutions? Because its fancy computer controlled differentials make the one in the i30n look like child's play and that's from over 15 years ago.

[@MrLunithy]

Cool like the RX in my RC .... lol on a serious note more of this stuff is great and any chance of some Peter Wherrett flash back that guy was way ahead of his time ..... in a few way's lol.