Toyota GR Corolla's Brilliant AWD System - How It Splits Torque!

How Toyota's GR-Four AWD System Works In The GR Corolla & GR Yaris
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How does the 2023 Toyota GR Corolla's AWD system work? GR-Four AWD is the first new sports AWD system Toyota has developed in over 20 years, implemented within the GR Corolla as well as the GR Yaris. The AWD system allows for three torque-split settings: Front, with a 60/40 front/rear split; Track, with a 50/50 split, and Rear, with a 30/70 split. How does it work? I spoke with Naoyuki Sakamoto, GR Corolla's chief engineer, to learn all about it!
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[@EngineeringExplained]

**Won't constant clutch slip create a ton of wear?!** Before you consider the system to be unreliable and inefficient, take a moment to think about what's happening inside an engine. You have a metal piston, sliding against a metal cylinder wall, thousands of times per minute, at ~60-90 miles per hour. And none of the comments seem worried about this? Rightfully, because cylinder walls use oil spray to minimize the friction and reduce the wear. In this clutchpack, we're talking about different materials, designed for the application, bathed in oil, with a massive surface area thanks to many clutch discs (spreads out the friction, minimizing wear). 0.7% slip is extremely low, and the friction created causes a torque to be sent to the rear wheels, thus most of the energy still goes towards powering the vehicle, with a tiny amount lost as heat. Still not convinced? Prior to this KZbin thing, I worked in the forklift industry. Some forklifts use the transmission to brake, rather than wheel brakes. These are wet, multi-plate clutch packs, exactly like you see here, and they do nearly *all* the braking for a 4-5 ton forklift. That's real heat, because brakes (in this case a clutch) are designed to turn kinetic energy (the forklift's movement) into heat. These clutches can last the life of the truck, thousands and thousands of hours. It's very cool, and pretty incredible! Not to mention, pretty much every multi-speed automatic transmission is using clutches. Heck, a single-disc, dry clutch inside a manual transmission, can also last the life of the car! 100,000 miles no problem, if you're not abusing it. My only point here is, before you assume it will fail, why not wait and see how it turns out? Toyota has a reputation for cranking out reliability. Why assume they haven't done the testing and validation this time? If there's info on GR Yaris burning up these clutch packs (it's been out for a bit now) - definitely let me know, and I'm happy to share information on it! I'll remain skeptical that the clutch pack is the big reliability concern for this vehicle. Edit: If anyone is curious how this differs from Golf R/Focus RS, I have a video explaining here! kzbin.info/www/bejne/aF7Cda2abJl6i6c

[@Hillwatch]

It’s so funny because that was the first thing that came to my mind. I really appreciate the extra info though and I will remain open minded.

[@Nobody-U-Want-2-Know]

4-5 ton forklifts are baby lifts.

[@TurboChicken313]

It still looks like electronically controlled honda crv rear diff.

[@relhen30]

Yes. I drive forklifts and very rarely use the breaks. I know someone that drives forklift for a different company, and they were told to never use the breaks.

[@Vo0Do0972]

Came to the comment section to ask this. Cool. Thanks. Haha

[@cromptank]

This reminds me of an AWD conversion for motorcycles where they have the front wheel driven slower (~33% if memory serves) but it’s hooked up through a freewheel. When the rear has traction it gets all the torque and the front is driven by the road faster than the chain, so front coasts like a bicycle would. But if the rear tire starts to spin the the chain driving the front catches up and starts distributing the torque.

[@The_Opinion_of_Matt]

You are thinking of Christini bikes I believe.

[@TarenGarond]

What Polaris(Four wheelers and stuff) call "real four wheel drive"(At least in some Swedish commercials a few years ago) is functioning like this(Separate freewheel for each front wheel, but electric engage when reversing and when decelarration in a "hill descent mode"), but for sure it is very very bad when doing work(Might be good in the swamps or whatever no idea, don't care XD)

[@EZ-D-FIANT]

Its actually quite common in reverse, Honda have done a few systems where a vehicle is front wheel drive but when the front slips the rears engage, I understand the issues with two wheel drive on a motorcycle and this would definitely help make one rideable, very interesting data thank-you I'm looking forward to learning more.....

[@tracylemme1375]

The Army deuce and a half trucks of the late sixties used a similar system with a sprag clutch between the transfer case and front final drive.

[@rmp5s]

I've never heard of this...going to have to look into it. Very interesting.

[@shadowboy813]

This system is basically a different way of implementing the AWD system Porsche used in the 959 over 35 years ago. The 959's AWD system used a clutch pack for a center differential and had wheels that spun at different rates, but it did this by staggering the overall diameter of the tires, instead of using transfer case gearing. The 959's rear tires spun faster because the front tires had a slightly larger overall diameter (about 1% larger). The 959's torque split varied from 50/50 to 20/80 (F/R).

[@agnttgr]

Actually smaller rear wheels cause counter-effect - front wheels start to travel more distance - 1 rotation of front wheels is equal of 0,99 rotation of rear, for example. Thus when multi plate clutch is locked - wheels rotate at the exact same speed and actually FRONT wheels start to slip, causing a movement of torque to the front wheels. I think this difference in tire sizes isn’t that noticeable because tires are tend to squeeze under load so this 1% doesn’t really matter. And actually Porsche AWD system is rear biased, when clutch isn’t locked, 100% of torque goes to rear. But what really interesting is that new Audi RS3 8Y has 14% larger rear wheels in diameter than front (this is 7% more distance at the same rotation frequency), so when clutches are locked - rear wheels tries to travel more distance and all of torque goes to the rear

[@holdenworth2076]

If youve never researched into it, you should do one on the Borg Warner AWD system in Cadillacs. 25/75 and can send 100% to either front or rear. Clutch pack instead of differential in the transfer case

[@AnthonyTrifoglio]

Which models?

[@zacharymurdock6721]

My SRX4 has it. Its great.

[@dann1s.365]

JTEKT supplies Type B Torsen LSD and ITCC for Toyota GR Yaris, it actually likes haldex (even technically simpler than old hydraulic Haldex) without the new torque vectoring provided by two separate clutch on the rear axle. It doesn't have like a mechanical center diff, it's not like an entirely brand new thing, a lot of car use ITCC like new cx60 and Outlander etc., but GR4 is kinda modified like using 12 pairs + 3 pairs (appears to be) of wet multi-plate clutch plates that distribute torque, probably in order to handle the enormous torque, and clutch plate uses carbon material to reduce heat problem etc. if you look back at Celica GT-Four's system, it had viscous coupling and locking center diff, more like (at least closer to) rally car

[@oldblueaccord2629]

...and how long did the viscous coupling last? Any thing Toyota does I call BS on....they just dont have it.

[@DistortShawn]

Saab X haldex

[@sddyck]

I've been excited to learn more about this system. You are the perfect person to explain it to me! Thank you!

[@EngineeringExplained]

Happy to hear it, thanks for watching!

[@Kyriaeus]

@@EngineeringExplained Judging from the comments, it might also be time for an in-depth video on the workings of a wet multiplate clutch. I think people have misconceptions about what causes or accelerates wear the most (heat), and they don't seem to grasp some of the fluid dynamics involved in a wet multiplate clutch (i.e. how the clutch plates can transfer force even through fluid shear).

[@Vermonstered]

@@Kyriaeus Do the math. 300hp engine with a 30f/70r split is 210hp to the rear. 0.7% of 210hp is 1.47hp that needs to be converted to heat nearly half any track lap.. Even cruising on the freeway you're talking about 1/2hp cooking in the clutch pack any time the car is moving. There's no cooler on the rear clutch pack, no circulation, has a fluid capacity of 0.5L, is within an inch or two of the rear exhaust pipe. There's no way to offload the heat. By the end of a typical track session you've boiled off all the oil if the system actually operated as EE describes. Instead it's just like all the other systems out there. GKN Twinster, SH-AWD, all operate in heavily biased FWD modes most of the time in order not to overheat and create heavy wear.

[@Kyriaeus]

@@Vermonstered Funny how you mention do the math, then fail at it. My point was addressed to the loads of comments moaning about "errmahgerrd the clutches are gonna wear out in 2 minutes!". But since you're here: 1. The engine is not constantly running at 300 HP, you'd need to be on a track that is nothing but a straight line and a CVT do that. Or be on a dyno. 2. Not all of the slip is taken up by the clutch pack itself. During tight corners the inside wheels will scrub and take up some of the slip. 3. The "up to 70%" rear torque bias is just hat - "up to". It's not constant and it's not an on-or-off switch. 4. A bevel ring-and-pinion assembly at 99% efficiency would generate more heat than the clutch pack slippage. 5. There's a thing called heat shields - without them the transmission on any longitudinal drivetrain would be cooked, and so would any FWD-based AWD system's front bevel box. 6. Congratulations on pointing out that a FWD-based AWD system is in fact FWD-based and shares characteristics with other FWD-based systems. Real galaxy brain move. Can the rear drive unit overheat? Yeah. Has it overheated in similar systems? Yeah. Can it be addressed by adding some cooling? Also yes.

[@Vermonstered]

@@Kyriaeus 🤦 it's amazing how much one can write and not understand when you don't have a cooling system it doesn't matter if the system is running at 300hp or 50hp. It's all heat soak with no offload ability. Astonishing how many excuses you can write and still not understand the basic premise of this is a car designed for track use. Half the lap is full cook with no cooling. None of your 'reasoning' explains how a system will not cook off 0.5L of differential fluid in a track session. The failure here is trying to explain away the initial pretense saying it doesn't exist. Lol never mind half your reasoning is flawed if not completely useless at best. Considering transmission coolers and much higher fluid capacities exist for the front bevel gear assembly and those have coolers. So sorry, math is still there and you still have to deal with the heat generated putting the pedal to the floor in a straight line. It's not a static state system like EE tries to explain.

[@codyhill6238]

EE I would love to see you do a video on how Subaru's DCCD functions. Most notably, for the 03-05 models they had a biased centre differential that would distribute 65% of torque to the rear without creating power loss through friction/clutches. As an engineer, I'm sure you can appreciate that. Further, this allowed them to independently free-spin axles if available torque permitted, but rarely occurs in standard cars through the DCCD clutches locking the axles together. Speaking of that, the DCCD clutch locking mechanism was quite novel too, using slip to assist in locking pressure.

[@Zer0Log1c]

This! I'd love to see a good break down of how it works. If memory serves, I think there was usage of a planetary gear set that was used to achieve the f/r bias but it's been a while since I dug through the cobbled together forum posts trying to explain it.

[@centralmoment]

The DCCD is a planetary gear, where the motor drives in on the bridge, drives forward on the sun gear and drives back on the ring gear. The planetary gear produces the 35:65 torque ratio. The sun gear and the ring gear are braked together with a lamellar clutch, thus promoting the 50:50 torque ratio, i.e. locking. This multi-plate clutch closes using an electromagnetic principle. Amazing and brilliant structure. A similar central differential was in the Lancia Delta HF Integrale.

[@nazhif1]

Been waiting for this video for the longest time. So basically it's very similar to the Focus RS's where the rear has higher gearing, but also like the Golf 7R where it has only one clutch pack before the diff

[@EngineeringExplained]

Yep! Though this is using a single clutch pack for the rear, the Golf R uses two, one for each axle (newest version, explained here: kzbin.info/www/bejne/aF7Cda2abJl6i6c), as does the Focus RS, but with a speed differential to allow for different torque splits.

[@Vlican]

Acura's SH-AWD operates in a similar way with overdriven rear wheels, but they go even further with torque vectoring between the two rear wheels.

[@EngineeringExplained]

I don't believe SH-AWD overdrives a whole axle, instead, it overdrives a wheel on an axle. Ex: The outside tire will spin faster than the inside tire on an axle.

[@Trickster_24]

@@EngineeringExplained youre mistaken. the 5th paragraph under 'development' on the wikipedia entry for shawd explains. id really enjoy a video explaining how shawd works and progressed. its an interesting system. most had the rear axle over driven at a constant 1.7% but earlier versions (that were used in the rl before it was discontinued) had an 'acceleration device' that let the overdrive be varied up to 5.7%. which allowed greater amounts of power be transfered to the rear axle. but i think it slightly limited the amount of power that could be kept in the front axle from 90% to 70-80%

[@tonamiplayman4305]

​@@EngineeringExplained The 1st gen SH-AWD system in the 2005 Honda Legend was more complex than this Toyota implementation, but used similar principles. This has a fixed gear overdrive of 0.7%, a multi-plate clutch and a differential. The 1st gen SH-AWD had a planetary gear set in front of the clutch pack acting as the accelerator with 1.7% overdrive which then connects to the left & right half shafts with their own set of planetary gears & multi-plate clutches. There was no conventional differential. However in order to save costs, the 2nd gen SH-AWD in the 2008 Acura TL dropped the Accelerator unit for a fixed gearing as is done with Toyota here, but with 1.7% overdrive instead of 0.7%. The loss of the planetary gear set on the central drive shaft reduced the torque distribution range especially in tighter corner. The 3rd gen SH-AWD in the 2014 Acura TLX took another cost reduction step dropping the 2 planetary gear sets from the half shafts replacing them with just 2 larger multi-plate clutches while keeping the fixed gear overdrive from the central drive shaft, but the ratio was increased to 2.7% This 3rd gen SH-AWD is very similar to the GKN Twinster used in the MK3 Ford Focus RS using 2 multi-plate clutches for each rear wheel. The central drive shaft though had a fixed overdrive ratio of 1.8% instead of 2.7%. Some versions had an additional multi-plate clutch upfront to disengage the rear wheels via the drive shaft for fuel savings. I see this Toyota AWD system as a further cost reduction from the SH-AWD & GKN Twinster. It replaces the 2 independent multi-plate rear wheel clutches with a conventional differential, while placing a single multi-plate clutch ahead of the differential. This is a much cheaper solution that can be deployed in more entry level vehicles by trading off a wider range of capability. so in order of complexity from high to low -SH-AWD 1st gen - 3 planetary gear sets + 3 multi-plate clutch packs -SH-AWD 2nd gen - 2 planetary gear sets + 2 multi-plate clutch packs -GKN Twinster - 3 multi-plate clutch packs -SH-AWD 3rd gen - 2 multi-plate clutch packs -Toyota GR AWD - 1 multi-plate clutch pack + conventional differential

[@traxxasslash95]

@@tonamiplayman4305 this comment is bang on

[@TML34]

@@tonamiplayman4305 The trade off isn’t capability, it’s more likely durability. But this is simpler, lighter and way more cost effective. Just know that you’ll need to replace clutch packs after x number of kms.

[@onemanmob6756]

It is a neat solution indeed. Similar way of sending more torque to the rear axle has been utilised in RC racing model cars for a long time. A beautiful thing about this drive system is that you can easily fine-tune it by putting slightly different outer diameter tyres on front and rear. By e.g. installing slightly smaller front tyres you could achieve a 80/20 rear bias instead of just 70/30

[@bradkroboth5490]

I've been a fan since I saw you in a car magazine a few yrs ago, love the content and explanations of how and why things occur, I have gotten both my kids watching you as well to expand their mindset

[@t16incho]

I have a GR Yaris and I was waiting so long for this video, non of the other videos (as always) go in detail to really understand the details. Thanks!

[@EngineeringExplained]

Heyy, happy to hear it! :)

[@robpeabo509]

You sounded and looked pretty excited about this development from Toyota Jason. It never ceases to amaze me what technologies are being developed for the motor vehicle. Just when you think that a particular aspect has reached it's climax, engineering AND science pulls another rabbit out of the hat. It is crazy! Motorcycles have had wet multiple clutch packs forever. You are actually taught to ride the clutch and increase the engine speed when performing ultra slow manoeuvres to remain stable I have been doing this for years and have never smelt let alone worn out a motorcycle clutch. I have never considered why multiple clutches are required, though I am guessing they each slip a little because of the oil, and the multiplication effect of each of the clutches in the pack help with overall clutch locking.

[@treaves2175]

Mostly a guess, but I think it’s also to distribute force/wear. More clutches means more distribution of wear means longer life id suspect!

[@michaelguerin56]

Thank you, Jason. I have wondered about variable axle torque ratios in on and off-road modes, for a while, especially after the Iveco Daily 4x4 came on the market here in NZ🇳🇿. The reports of central (electronically controlled) differentials causing vehicle fires (in hot places like Arizona) due to differing rolling diameters of vehicle tyres now make more sense to me. I will not attempt to explicate these details to anyone else, rather I shall point them to this video🙂!

[@TheGuyBooth]

Great explanation! Your videos are always extremely informative. It was a pleasure meeting you at the Toyota event and driving some fun cars at the track! Wishing you all the best!

[@EngineeringExplained]

Thanks!!

[@fp5495]

I watch these videos knowing I have the mildest of understanding of what is being explained, but still appreciate them with 100% gratitude. Impressive knowledge, as is the knowledge in a lot of the comments, as well.

[@yr6sport418]

You are constantly successfull make such a complex thing looks more more simple. Very good explanation.

[@EngineeringExplained]

Happy to hear it, thanks for watching!

[@commonsensicalkurt]

The focus RS has 2 clutches on each drive axle going to the rear wheels instead of 1 before the diff, and as a result the rear diff is locked because it can let the clutches slip to change wheel speed left to right instead of needing the diff to do it. This makes it possible to send 70% engine torque to either rear wheel.

[@kinglouiesshed8995]

Is that not what a mechanical LSD is for ? Just more things to put torque in to in my humble opinion 🤓

[@commonsensicalkurt]

@@kinglouiesshed8995 mechanical lsds will limit the difference in speed between each tire on an axle, but it has no active control over the torque split left and right. The clutch pack method can close one clutch and open the other sending all power to 1 side, or close them both and lock the wheels at 50/50 or an combination in between. It's a more versatile system then an lsd that let's the tires slip a certain amount and then when that limit is exceeded locks the axle at a 50/50 split.

[@sity909]

ok that's old tech. We're talking about the GR Corolla now.

[@diegogar400]

Old American engineering now we looking at what Japan has to offer bro

[@rangerover06sc]

@@kinglouiesshed8995 Well some of the differences are that a mechanical LSD is reactive not active. Also mechanical LSDs still let the unloaded wheel spin faster. It just limits that. And typically poorly if the wheel is off the ground because there is not enough torque for the LSD to lock. The diff in the focus can actively control wheel speed and the torque split pro-actively

[@TheGinger1]

Now I understand why I've seen videos of the Yaris being tuned with only the front wheels on a rolling road. Thanks as always for the great content!

[@randyhill7635]

I've been wondering what AWD system this car has since I first heard about it. You are the first one to answer my question. Thanks Jason, keep up the good work.

[@carlwillows]

Borg warner has made a TOD (torque on demand) transfer case for decades now. Very similar. 9 clutch plates I believe.

[@4x4.tests.on.rollers]

Interesting thing is that Mazda is using exactly the same system as Toyota (ITCC by JTEKT) but with 1% overdrive ratio. However - they are not using it to send more torque to the back but only to eliminate the backlash of the drivetrain.

[@LaBambaCL]

i rem a video by the mazda chief engineer, sounding something like this. this video title is misleading, its not brilliant, at least he didnt say new. and it doesnt sound as good as torque vectoring sh-awd.

[@dann1s.365]

lol I think I talked with you about the cx60 AWD system, yep it used itcc too

[@4x4.tests.on.rollers]

@@dann1s.365 On my channel? I believe CX-60 uses ITCC to but I meant fwd based models with the same layout as Toyota. Some years ago they've been cooperating with GKN but probably switched to JTEKT when CX-30 hit the market.

[@kolbenkopp-8780]

Fantastic vid explaining the (at least for me ;-) counter intuitive physics really well. And the tip RE "track mode for sliding" coming in handy. Got our Yaris a few weeks back (after a looong wait). In the dry it's an absolute monster. But quite happy there's finally some rain over here :-).

[@GR_Papi]

Very true about 50/50 drifts I’ve done it unintentionally a few times with my 07 Sti with the diff in full lock pretty wild sliding like that.

[@ProfessionalFixologist]

Great video as always! Could you do a follow-up for how this works when cornering, with different inside and outside wheel speeds? It seems like the difference in speed would cause the rear wheels when cornering to want to slide further out when the clutches are strongly engaged, and track more to the inside when lightly engaged.

[@EngineeringExplained]

The torsen diffs front and rear will take care of the left/right speed differences. The clutch simply chooses which axle gets more torque.

[@azlktune]

The clutch is never fully locked, it just limits torque on rear wheels. So when front wheels are running faster, it will just have more then initial 0.7% slip. Same happens in any modern cheap crossover without center diff.

[@calholli]

I think there is a VW that has a similar setup to this, in that the rear wheels are over geared just a bit. I know that the Acura SH-AWD system has a planetary gearset on each rear wheel, which acts basically like a 2 speed transmission on each rear axle; and has clutches that can engage on or off to disengage the rear wheels and allow it to be only front wheel drive most of the time.. I believe there are actuators that the computer can use to shift those planetary gears on the rear axle, into "over geared" - so that the rear wheel then get all the torque. Very similar to this system, except it has 2 of everything-- and the "over gear" in the rear is not permanent-- it's only engaged when it is needed on corners and low traction... In other words, the clutches in the rear can be fully locked, and still have a 1:1 ratio at all four wheels. So the AWD clutches, and the planetary "over gearing" are two separately controlled systems.... This Toyota setup is a much simpler and much cheaper version of that, but with less independent function.

[@alpanex21]

Like other commenters below, I was really waiting for a video like this! And here it is! Softening my pain that my GRY has not yet been delivered. Currently 17 months after order.

[@thenitekid]

I have a GR Yaris and i knew a bit about how the 4WD system works, but not to this extent! Haha! Nice video as usual, always a good explanation of everything. Keen to see you and others do more videos on Toyota's AWD 3 cylinder platform as America now gets a version of it in the GR Corolla.

[@MatthewHartsuch]

I am extremely excited about the Corolla GR, especially after seeing what the yaris gr is capable of.

[@absolutelyfailz4480]

Toyota Corolla with the GR trim sounds cool. My girlfriend laughed at me when I said toyota corolla gr and she said "nah we'll keep taking my lexus and you can leave your corolla at home". We were talking about date nights after I get my new corolla GR

[@DziadekMroz6666]

In heavy track use rear diff overheats in GR Yaris and then it goes to FWD mode It's mostly caused by exhaust being pretty close

[@kentowers2802]

The rear diff only take 0.5litres of oil A larger cover plate is available to increase the oil quality inside the casing. The clutch pack is separate though and yes very close to the exhaust

[@oldblueaccord2629]

Like ZERO surprises there...once you said Toyota.

[@kentowers2802]

I have changed my gearbox, transfer and rear diff oil twice now in 3000 miles The transfer case oil was dirty but the rear diff oil was very black and the plug magnet was covered in sludge Toyota say to replace oil every 4th year but that’s too long

[@kentowers2802]

@Way Outthere the GR/TRD undertray is for cooling the front transfer case and gearbox. It’s the rear diff which can overheat. The engine under tray won’t increase any cooling to the rear The part is also difficult to source from U.K. dealers

[@user-sq6nu3rv1m]

This is sounding like a real alternative to the current WRX, if availability doesn't become a problem. 🤔 Looking forward to seeing the inevitable head-to-head comparisons.

[@NackteTraube]

From what o saw only about 6000 manual gr Corollas will be sold in the us 🥲

[@jackemarleeyoung]

It won’t really be a good comparison when the price difference would be close to $10000. Maybe it would be comparable to the golf R, or maybe even an Audi.

[@robpetersen87]

@@NackteTraube it's closer to 5,000 due to production issues, but that's also just for the first year. There will be plenty more to come in later model years.

[@treaves2175]

Leaks are saying this starts at about 38k without the LSD front & rear

[@robpetersen87]

@@treaves2175 Pricing got announced, it starts at $35,900 without any options. A fully loaded Core with all three options packages comes out at right around $40k after destination fee.

[@DirtSweatGears]

Thank the engineers that they used Torsen limited slip instead of throwing more clutches at it. Much more durable, and there's only one set of extra clutches before the rear box. Toyota can do some great stuff when they actually do the work!

[@jg8263]

The fact that more vehicles don't use Torsen is a shame. Such a great and robust system.

[@MiikeyLawless]

@@jg8263 but it does have a big downside...

[@jsquared1013]

@@MiikeyLawless a simple preload spring in the center (as in the Wavetracs) takes care of the diff acting open when one wheel is totally unloaded.

[@aaACEa]

Gears, transmissions primarily on alignment, synchronisation, precision and timing. Manual transmission is the beauty of the art of driving. Bravo always. 👏

[@apexhugger]

Great video Jason!

[@matthew3136]

My first car was a rwd Corolla. I would love to get one of these bad boys. Sadly, they will be hard to find at reasonable prices.

[@427cidpower]

They will be impossible to find at reasonable prices 😱

[@danoberste8146]

EE, you are amazing at anticipating all of my questions. This video was an an ALMOST perfect example. You nailed 999 of my 1000 questions. The one you didn't address is how much torque can you sap from the engine in the worst case scenario? Drag and heat have got to cost something. Did Toyota just give the motor more power than it can possible use to overcome the loss? Thanks,

[@Incommensurabilities]

Good point. Traditional AWD/4WD systems sap a lot of power if they're engaged all the time, so I would be surprised if this system was any worse overall since I would expect that most of the time it would be 60/40 front/rear

[@EngineeringExplained]

Great question - I do not know! Dang. But considering this thing has nearly equal fuel-economy the lighter, FWD only Civic Type-R, I don't think it's eating up much energy. There of course will be some energy lost as heat in the clutch pack - I do not know what that number is. Again, great question!

[@stefano-hd6es]

Amazing explanation, such concepts explained simply, even for non-native english speakers like me! Thanks!

[@EngineeringExplained]

Glad it was helpful!

[@cattman1970]

Well done. Love your explanations

[@jamte6150]

This car is going to be limited in production. I wonder if this system will make it into any other cars? Before multi motor EVs take over and can do more for less. Can’t wait for the full review !

[@sssxxxttt]

Yea, why develop something like this when many states consider banning ICEs in less than eight years?

[@joeyager8479]

You're comment about EVs beat me to it!

[@adrianbjones]

Exactly - what a waste of time compared to 4 in-wheel electric motors.

[@frijoli9579]

If only EV's were light and stored a lot of energy. Gasoline is still king for years to come. Maybe one day soon there will be the nail in the coffin, until then leave me to my own choice. lol

[@alexanderflack566]

@@adrianbjones In-wheel electric motors are a lot of unsprung weight, which will negatively affect handling. Even with them in the car instead of the wheels, you probably don't want 4 in a road vehicle just because you're increasing the cost for very little benefit; an LSD and independently powered front and rear axles is already far better than you can get with any reasonable ICE-only car setup.

[@wompa70]

Glad you mentioned the center clutch pack was wet. I was imagining just how fast that would wear out since it's always going to be slipping. This little machine is amazing. Wish I could get one.

[@AgneDei]

With pretty much constant slip in many modes it will still wear out fast. Oil won't help with that completely. I guess that there are lots of sensors in that clutch pack to precisely measure it's temperature, and most likely software in the car will disengage it before it overheats, but it will still wear out quite fast as it will wear out even when cold slipping. Also it would be interesting to know how much a replacement set of clutch disks costs for the Corolla and Yaris GR. As it is a Toyota i guess that they expect you to mostly drive around in Auto mode with 2wd, and really pushing it like once a month for an hour or two it may easily live though 2-3 years and that's really all you apparently need in a new car as you throw it out after that anyways 😉

[@EngineeringExplained]

@@AgneDei Why make up numbers haha? 2-3 years? You really think Toyota's gonna make a part that consistently fails within warranty? Also, there is no "auto" mode, no 2WD mode. It's always AWD. Please read pinned comment above for durability concerns.

[@mrwhips3623]

@@AgneDei you and a rock have the same IQ. You clearly know nothing about these "wet clutches" so instead you came up with a bunch of BS numbers. Bruhhhhh 😂

[@AgneDei]

@@EngineeringExplained For a sort of science driven person you are really naive in belief that a constantly slipping clutch can physically be reliable. It's not hydrokinetic, the slip still wears down the clutch material, the oil just prevents it from burning up quickly. Any motorcycle owner with a multi disk wet clutch will agree with that FACT. I assumed that there is an auto 2wd mode as that would make obvious sense with what you described. It's how literally almost all 4wd systems work nowadays in cars with traverse mounted engines, and by pure statistic it's highly unlikely that all of them did it wrong, and only Toyota knows how to do this. 2-3 years(maybe 4, by the way in EU the standard consumer warranty is 2 years long, while a standard warranty for business is only 1 year) is most likely exactly after the end of extended warranty and that's exactly what manufacturers are doing for years already, making cars after their lease as expensive to maintain as possible, to make new lease more attractive to the customer, than keeping/buying out their car after the lease ends(this drives new car sales hard for many years already). Also as to the warranty, I'll be very surprised if Toyota has a warranty on that clutch, which is basically never under warranty as a normal consumable part. As to the "explanation comment", cylinder wall and piston are designed for low friction, they often have ceramic coating to reduce friction, and they are sprayed with engine oil, which is slippery, and a totally different kind of oil than a gearbox oil designed for wet clutch. If you used engine oil in that clutch pack it would most likely stop working as it would really start slipping like crazy. That's the reason why you can't even put normal gearbox oil(not to mention engine oil) to a wet clutch setup or you'll break it. That's seriously basics of wet clutch operation. I can believe that Toyota put a lot of engineering to limit this effect, and oversize the clutch so that is has lots of material to chew through, maybe a big filter to catch the ground up material, but in the end, physics is physics, and unlike the engine example, clutch disks are designed to grip, not to slip. I'm quite sure that they would talk a lot more about the clutch if they managed to make a hybrid of a hydrokinetic clutch (where slipping only heats up the oil instead of grinding down metal parts), and a normal friction multi-disk clutch (as in haldex, dsg, motorcycles, and lots more).

[@danoberste8146]

@@AgneDei Or... does the wet clutch act more like a torque convertor? If the pack uses ATF there may not be any actual physical contact between the plate and the clutch. Caveat, I'm no engineer and I don't know, but I agree with EE that Toyota wouldn't design a component that is guaranteed to fail during the warranty period.🤷🏾‍♂

[@philips3825]

Much awesome. Thank you J!

[@edwoodcostin]

Great video. Brilliant explanation thanks

[@evchargerreviewsnet]

Thanks Jason! What an amazingly complex engineering solution for converting dino juice into forward traction. So much more simple and reliable to have an electric motor at each axle...

[@cromptank]

One negative here: If you tune up that engine, the clutch pack can still only draw so much torque for the rear so beyond a certain point all your torque improvements go to just the front axle. Upgrades focused on making that engine rev high and carry the same torque longer wouldn’t have this problem though.

[@ryancooke8429]

I've seen some people crack the controller for the system and are able to send more rear power than factory, I guess they up the clutch pressure

[@cromptank]

@@ryancooke8429 I think the issue is it can only handle so much torque continuously before overheating. Maybe giving that clutch its own oil cooler is possible.

[@ryancooke8429]

@@cromptank yes I'm sure at some point it would need better cooling and or upgraded clutch plates, but it seems like the system is still pretty effective in the 400+HP range, plenty for a small car

[@capnskiddies]

It weighs as much as a pair of boots. And it's 285 from a 1.6 3cyl I'm not sure how much power has been left on the table before reliability/service intervals become a pain in the arse.

[@cromptank]

@@capnskiddies that’s an excellent point

[@robpetersen87]

Looking forward to your review! I hope the GR Corolla is good, because I'm getting one...

[@EngineeringExplained]

Coming soon!

[@SeaCTV]

I literally looked up: "GRC system engineering explained" two days ago. It seems I was two days too early 😅 Cheers, thanks for the lesson. This alongside the MK8 Golf R/Focus Re video really helped me understand the different approaches. Excited to see how the GRC overheating is compared to the GRY considering it will default to FWD if it gets a little toasty.

[@Consolethumbs]

This will be fun to test when we get them at are dealer so far the best AWD system I tested was Acura SH-AWD or IVTM-4. 3 inch lift on the GR corrola will be winter monster.

[@Dma63]

How about 4matic mercedes? Is it the same thing like these?

[@jacquesc3166]

Have you tried the DWS06's in temps below -15C though? Down right dangerous in Canada, you'd slide off the road if you attempted to show off. I get the ground clearance aspect though, I have failed to care in the past and parked my sedan after plowing through salted snow on the roads and 10-12 inches of fresh powder in the lot. Rust will happen, no matter if you Krown it.

[@jacquesc3166]

@@username8644 I bet it does. I've been running ATTESA-ETS in my daily for 12 years between an 06 G35x and this 13 G37xS, car is 95-5 rear bias and goes up to 50-50 as rear traction goes out. I would say symmetrical AWD is more capable, but an NA V6 that screams to 7,500 RPM while sending 70-80-90% to the rear is more fun. Respectfully.

[@josephpiskac2781]

I had a similar system on my 1984 AMC Eagle SX4. I could take the car on ice covered roads and the car performed like it was dry pavement.

[@ROCCOCYCLES]

I actually saw one of these last weekend. It was lifted with big tires. Odd bird.

[@josephpiskac2781]

@@ROCCOCYCLES They came from the factory with big all terrain tires. Mine was beautiful with silver body and navy blue mud bottom trim. Navy blue or slightly lighter blue interior with every option. The straight six was developed for the 1962 jeep and the torque would pin me to the bucket sear. Performance out of this world off road and in winter. One time I was stuck in a snow drift so I gunned the engine and all four wheels rotated with the car lifting on topof the snow. I drove on top of the snow possibly for a mile. Sadly I started having extreme maintenance problems after a couple of years and felt forced to trade it in for a new 1987 GMC Jimmy.

[@kc9scott]

I believe the Eagle used a viscous-fluid-coupling center diff. I have a DSM that also uses that type of center diff. Those are fine for basic winter traction, but in sporty driving, it takes a few seconds for the viscous fluid to heat up and provide traction to the other end of the car. That delay is annoying.

[@josephpiskac2781]

@@kc9scott Yes mine had I think 16 maybe 9 clutches in viscose liquid. The torque converter was hand built in England. Ifthe wheels were spinning it required a second or two to halt the spin. On an ice covered road it seems to have always been working. Acceleration on ice was amazing.

[@jimbodee4043]

Thanks Jason for the 12 disc oil filled clutch pack assurance as I was not believing it would not wear out in like 1000 miles of driving.

[@xulloa84]

Those three cilinders on top 👍, great video as usual top notch

[@mikebeale1685]

In your explanation about why it might be possible to send 100% of the torque tto the rear in higher gears, but not lower gears you compare wheel torque values. These torques are not what the clutch pack sees because it is located on the driveshaft before the final drive. The torque values are lower by about a factor of 4.

[@EngineeringExplained]

Okay, quick clarification here. It's possible you're correct, but I don't believe it's the case. You have the bevel box turning the rear driveshaft, and then the rear driveshaft turning the final diff. If these gear ratios match (one speeds up, one slows down), isn't that 1:1? Further context, this transmission has two final drive ratios. One for gears 1-4, and one for gears 5-6. This indicates there are two output shafts in the transmission which mate to the front differential (bevel box, here), thus allowing for the two final drives. Then you have the gear ratio of your rear driveshaft at *both* ends. If those match, wouldn't it balance out?

[@andrewsnow7386]

@@EngineeringExplained I was going to make the same comment as Mike, but after deciphering your reply, here is my revised comment: The combination of the bevel box and rear differential ring and pinion must be responsible for the 0.7% speed difference -- that is there combined ratio must be 1.007:1 not 1:1. But, that doesn't tell us the torque through the clutch pack. We would need the actual ration of either the bevel box or rear diff to determine this. Now, (as expected) we can see in the cutaway photo that the pinion in the rear diff is substantially smaller than the ring gear -- maybe 3:1 maybe 4:1. So I agree with Mike. The torque in the front to rear drive shaft, and thus the clutch, will be 1/3 or 1/4 the torque you calculated for the front differential carrier housing.

[@crazybuschris]

@@EngineeringExplained That is assuming the bevel box ratio is 1:1 which from the photo of the rear diff it is not. The torque at the clutchpack would be reduced by whatever ratio is used for the bevel box/rear diff. As a point of comparison, Haldex systems typically use a 1.6:1 gear ratio in their bevel box.

[@4x4.tests.on.rollers]

@@andrewsnow7386 In the transfer teeth ratio is 17/39, in the rear differential - 41/18.

[@andrewsnow7386]

@@4x4.tests.on.rollers Nice - so about a 1:2.3 ratio at the bevel box (not quite between the 1:3 or 1:4 I was guessing). Thus, the torques at 9:58 in the video would be 1,700 and 370 lb-ft.

[@hardcoreep]

Did you see the Japanese tuner Revolution's GR Yaris. They found out that past 45kg of torque the car goes100 percent front-wheel drive. They had to get an aftermarket computer to stop the car from doing that. Now if the GR Yaris shares the same system as the GR Corolla, will it be programmed to do the same?

[@hardcoreep]

@Way Outthere I'm aware of the motive car, but they're not using a stock ecu + parts and if I remember correctly, they specifically tuned it with a power ramp. Not all of us want to go that route.

[@SBKhuram]

You're the best!! We love you!

[@larsweinand4035]

well, in the GR Yaris, it overheats after 10-12 laps on the track - that's with 255s AR1 Semis... but happens. Then it puts it into 2WD mode only.... works fine again after cooled down. The close by exhaust adds to this happening... but there are some vents you can install which blow cool air onto the clutch housing.... that helps. Love that car :)

[@TheAnoniemo]

I wonder how much energy is being lost in the clutch slip, compared to a geared AWD system. This sounds like a way to make a cheap compact AWD system but sacrificing efficiency or long term reliability, bit like a gimmick. edit: Not trying to hate on it, I'm sure it's fun to drive in the AWD modes and you wouldn't be driving for best efficiency anyways when you enable them.

[@luizarthurbrito]

Yeah, I agree that the cheaper tried and tested reliable way of doing 4wd fits a Corolla better than this system. But what do I know haha.

[@ivonakis]

Here is my though process - If the clutch is fully open the car is front wheel drive and 100 percent efficient. If the clutch is welded and the wheels cannot slip the car will bind and will be 0 percent efficient So if the front wheel get 60Nm and travel 100m and the rear wheel get 4Nm and travel 100m the energy lost is 40nm - slip which is 0.7m. So the car did 1000Nmm and lost 28Nmm Sorry for the confusing units. So the efficiency is 1000/1028 or 97 percent. If we calc for 30/70 - the lost energy is 49Nmm and the efficiency is 1000/1049 or 95 percent.

[@jbandt]

@@ivonakis units aside, you're explanation helped. I too was wondering how much efficiency is lost by slowing the front axle to send more torque to the rear. It sounded like it was creating a lot of drag making it pretty inefficient.

[@EngineeringExplained]

Y'all are incredible - company develops a neat way for you, as the driver, to have selectable torque splits, and you say "it's a gimmick." Gets way better mpg than Subaru STI, what efficiency do you want to see from it? How is it unreliable?

[@davidlobaugh4490]

AWD wasn't broke no need to fix it.

[@tristianbilly001]

Whiteboard connoisseur

[@MannySilva]

My 2003 Mazda Tribute (aka Ford escape) had a similar system the clutch pack locked up at around 10 years old and was in 4 wheel all the time making for a stiffer and more noisy ride, Lower MPG, etc.

[@joshuafaircloth4098]

Awesome video, very well explained

[@hondartluke3219]

First thing great presentation as always. Second I never comment but besides the fact. This system isn't new and almost seems Toyota took this right out of the Honda playbook of all things engineering. Also the experience and knowledge of such an exact replica will tell you it's very unreliable. Back when Honda used an actual viscous coupler it was more guaranteed and had some longevity but then Honda reinvented the deployment of the system to incorporate "wet clutch" technology. Look, any Honda guy will tell you it's a garbage system that has been extremely modified in the aftermarket just to have progress in the racing records worldwide. Honda has advanced from this to the SH-AWD version of the "realtime" basics they once utilized placing more "wet clutches" at each piece of drivetrain that transfers the torque and is amazing stuff. I must say again, this is archaic technology and quite surprised Toyota had to copy such an old relic of engineering. 1984 Honda Civic wagon RT4WD is where my knowledge starts on Honda dominating this technology since then.

[@mattg9364]

So basically the same as a focus RS or older golf R? Basically an over run haldex system.... nothing earth shattering really, this has been a thing for a long long time

[@killmeh2]

yea, it's still an economy sports car in the end

[@mattg9364]

@@killmeh2 yeah just don't know why the vid ranting and raving over something that's just a copy and paste of what everyone else is doing

[@ALMX5DP]

@@mattg9364 it’s similar but not identical. I think it’s still beneficial to cover the nuances to understand the pros and cons to each approach.

[@albertobrancati]

Golf is 2wd in normal condition, GR is always 4wd

[@mattg9364]

@@albertobrancati yeah but it's the exact same system

[@v-gc7257]

I want one. Thank you Toyota. Beautiful engineered.

[@SONO4B11T]

Definitely going to have to watch this video more than once.

[@Ballacha]

that looks unnecessarily complicated. why don't they just go permanent 4wd like evos? fuel economy? i mean, according to this video, the transfer case clutch pack is almost always engaged, unlike vw's haldex. so it's not even going to be as fuel efficient as part time 4wds. not only that, you also have clutch grinding all the time. why?

[@HuffmanDickings]

already seen videos of people posting how their corolla went into 2wd mode due to heat. this is a cool explainer thanks!

[@aaronwestley3239]

Well there's a reason why Toyota dominated the WRC for many years

[@wsu8568]

If you would call 2 out of 20 “dominating”

[@aaronwestley3239]

@@wsu8568 well they have 60 rally victories, with only 2 manufacturers beating that record, one of them dead. Plus 4 constructors title.

[@CharlesChristena]

Good job Jayson

[@Tanktaco]

Love these more technical white board stuff, but I think I'm gonna need to watch it again.

[@mikeormond7883]

In the U.K. the centre clutch packs regularly overheat on trackdays in moderate to cold outside temperatures when used hard for longer than 10 minutes causing an “overheat” message on the dash and converts for fwd.

[@cybertrk]

Another clutch to replace

[@JordieG8]

Nope

[@ALMX5DP]

Probably should pay attention to the latter portion of the video.

[@jharris280zx]

I remember a certain youtuber driving a subaru impreza and comparing the awd system to a mitsubishi lancer awd and hearing him say subaru applies brakes to the inside wheels when turning, while mitsubishi adds power to outside wheels to help corner.

[@LalaneMotors]

Thanks for this!

[@cameronturnbow8004]

In the racing GR Yaris, they set them up to do 100/0 torque splits when they pull the handbrake. So there are applications for the 100/0 split.

[@Disnamesucksass]

This is for all the GR yaris'. "Pov" spec or rallee

[@rsanchez9865]

Great video, thanks

[@dr-zieg]

Reminds me of tuning the slipper clutch on my old RC.

[@darthkahnobis]

Love the subtle Lebowski reference

[@ericvermeulen9853]

Own a GR Yari with the LS diffs, it is the best in its 50/50 setting although it doesn’t always feel like a 50/50 split when on track but more neutral

[@brandonroyal6821]

As a mechanical engineer who also trains students, I love your videos, but I have one hangup. I would suggest replacing the word "torque" throughout the whole video with "rotational speed". Overdriving a mechanical apparatus through gearing does not increase the torque applied, it actually reduces torque applied - but what it does increase is RPM!

[@JackOfHearts42]

Love the drivetrain videos!

[@FableReality]

I feel like I've been waiting for this video for over a year

[@dalekallio4619]

It seems that data, once again, wins the day. Bracketing torque and distribution of it, via gear angles that can take a beating👍🏻

[@ScarKnoturbed]

Amazing tech 💯💎

[@ThunderbirdRocket]

Nice one ! Thanks .

[@chapystick_]

This is mind blowing for me because this is how the AWD system of the Mazdaspeed6 works, except that it came out in 2005. As far as I’m aware though, the rear diff gear ratio matches the front so it’s maximum split is 50/50 or more front biased. Looking into my resources to see if it’s actually geared faster or not to confirm.

[@elmeleegy9904]

Thanks for explanation. One question I have is what would happen if you have smaller wheels in front than rear or vice versa? How would that impact the slippage in the clutch pack?

[@ianmusson5883]

Thanks for the explanation. Looking at the way the torque split works it relys on the car having consistant wheel road speeds on all for corners. So the car will need all four tyres to be the same make, wear and tyre pressures to make full use of the system.

[@hieuhughesle-au9884]

really interesting stuff, this reminds me of hondas iVTM/ Acura SH-AWD but instead of longitudinally across the rear wheels more or less vertically between the rear differential and front transaxle; with the difference being multi ratio front or rear power bias in the GHR compared to Torque Vectoring front or rear power bias on honda AWD systems

[@sodazman]

I've had my GR Yaris since launch and it's overheated at least a dozen times with enthusiastic street driving, track driving and skid pan runs. I'm going to try wrapping the exhaust as some suggested and hopefully it remedies the problem.

[@krebgurfson5732]

absolutely not bro, get a subaru

[@MO-on8ml]

great video as always :0)

[@jojo_beans]

Hey I recognize that track! It's the Utah Motorsports Campus. That's a fun track that's really wide and really fast.

[@robertrousseaux1059]

Winter climate means an AWD sports car . This awesome.

[@josephpiskac2781]

Jason looks like your putting on some muscle. Good deal!

[@Angry_Squirrel555]

I can’t wait for your review of the GR Corolla. This vid has been truly enlightening and I learned a lot about this car, now I REALLY want it! I’ve been a Civic guy for a while but this is just seems to be a really promising car like the old SE-R, JCW Mini, DS3, etc. Plus the new Civics (as nice as the Type-R is) have gotten far too large and the GR is a good looking car that’s small.

[@DeFausti]

GR Yaris is much better though

[@annettesurfer]

More complexity just means another component that could go wrong. This great engineering reminds me of when direct fuel injection replaced port injection and whether the consequence was unintended or planned obsolescence.

[@tinhinnh]

The beauty of this system is its adjustable

[@yungboicontigo9278]

Toyota has been on a roll in the past couple years. I’m not a hot hatch kinda guy but would love to buy a GR Corolla at some point. Definitely giving the Civic Type R a run for its money!

[@Squeezmo]

Kinda the same process when paralleling AC generators. If you make one try to spin faster when locked together, the faster machine picks up load from the machine set to run slower, although both must spin at the same speed.

[@ryoder]

Loved the Lebowski reference! ;-)

[@peterscott4597]

Thanks!

[@gw4686]

You had me and then you lost me at 5min 44s. But thankfully I can watch til the end & replay until I understand🤣 🤣 . And eventually be less lost, hopefully. You are a good man. Thank you for making us simpleton feel like we can understand engr

[@gw4686]

Only thing that didn't compute was that the heat within the clutch pack ~ 'losses' through the drivetrain. Why it is convenient to use percentage splits rather than thinking exact torque numbers.

[@freecanadaplease]

Living in Canada and driving old quattros this is the first car that has interested me in a long time. I've driven haldex cars with great disappointment, but how does this compare to the new golf r / rs3 haldex ? New haldex seems like they are trying to engineer out the flaws of haldex (wider front tires on rs3) and less grippy tires on the rear of golf r press cars. The GR looks like the closest thing I can get to my 2000 Audi a4 b5 1.8t with rs 4to1 center diff and torsen front and rear.