Quattro vs. Symmetrical

[Beanboy]

Who's confused? I think it is a terminology issue more than anything if any confusion does exist.

 

Seriously, I think many Subaru fans are stubborn to see some advantages the latest performance versions of the Haldex systems have to offer.

 

For the on-road performance driving like the LGT was designed for, I think it is really tough to predict what system would be faster...Given how quickly Haldex is improving, I wouldn't be surprised that the latest one in the MS6/improved R32 given everything else equal would result in better laptimes given exactly the same vehicle.

 

Yes, Haldex has no center diff and only offers partial/full lock during certain situations. So what? Willing to bet in situations where the Subaru system would be at an advantage, the parameters would be set for the Haldex system to be working. And as an added bonus, already locked along with offering stability control.

 

On the subject of stability control, Subaru will need to work on a different center limited slip system since stability control is going to be required for cars in the LGT class when the next generation LGT is released in a few years.

[RobY]

Well what exactly are the performance advanatges? If none of the wheels are slipping as is on the the tarmac haldex can only deliver 50% max to the rear wheels. Subaru already has this as its static distribution. Haldex cant shift power forward and back... it can only shift power back.

 

Mid turn you can never have full lock in a haldex system since there are no differentals the coupling will bind the drivetrain like a 4x4 vehicle with a transfer case.

 

In fact if there is ANY power transfer to transfer to the rear wheels mid turn it will cause some sort of binding, albeit not noticable, because a coupling by definition will try to make all the wheels spin together at the same time instead of allowing diffrent wheels to spin freely as is is required mid turn.

 

The sharper the turn the more you need AWD the less active the haldex system must be to allow the wheels to spin freely. If it fully engages the front wheels which are spinning faster than the rear wheels mid turn will try to mesh together causing some pretty frightening stuff to happen. Oversteer and understeer at the same time alternating, who knows it depends on which set of tires loose grip first as a result of wheels spinning at diffrent rates and a coupling trying to mesh them together when the driver adds power. This is unavoidable in a coupling.

 

If we look deeply into the technical aspects of haldex it is not made as a performance AWD system. There are technical shortcomings that a true differental system completely avoids. Sure subaru's system isnt perfect but it does offer real advantages over part time active AWD.

 

If you want the ultimate AWD get a computer based differental system like Hondas SH-AWD, ATESSA, VTD, or Misubishis ACD. Ill be first to admit that these systems are the cream of the crop and in almost all ways better.

 

Im not denying the benefits of computer control, but haldex is not designed to be a performance implementaion of it. It can be made to perform well and it is certainly better than FWD but is has technical shortcomings.

[Scotty]

Actually Haldex can be developed for performance. Their new aftermarket software is set up to respond quicker by throttle input and input speed. The new set up is biased towards the rear. If you mash on the throttle, it'll go to full lock before the engine responds to the throttle input. The OEM software is reacting in about 1/7 rotation of the wheel.

 

Of course the Haldex system can be configured on a RWD car like the Lamborghini Gallardo.

[RobY]

It can be improved yes. But any improvement you make will still be limited by its shortcomings. Powering out of a turn if the haldex ever attempts to go full lock you will loop the car because it tries to sync the front and rear wheels together. Without diffrerentials the wheels cannot spin independently while still delivering power. Any amount of haldex lock will impart a syncing effect on the front and rear set of wheels which are spinning at diffrent rates.

 

All this more agressive software is great but the last place I want the haldex to lock up is when agressively powering out of an increasing radius turn causing me to completely loose it when my rear wheels which are spinning slower than the front wheels mid turn decide to match each other in speed at the limits of adhesion.

 

The more it locks the more it tries to sync the drivetrain together and force wheels spinning at diffrent rates to spin at the same rate. To prevent this it has to decouple partially if the computer detects a change in steering input. In performance situations, ie corner exit, hairpins, sweepers, it takes away AWD when you need it the most.

 

Haldex can be configured in RWD but its a question if it offers any perfrormance benefit over RWD alone. Many Lambo competitors use an MR 2wd setup and outperform it oftentimes with less power.

 

 

By definitition it can never be rear biased its just a clutchpack that takes power from the front and attempts to couple the front and rear wheels together.

 

Haldex can be defined as an automaticly acting part-time AWD system since it lacks a center diffrential.

 

Visual aids...

 

http://www.4x4abc.com/images/101/4WD_turn.jpeg

 

http://www.4x4abc.com/4WD101/def_turn.html

 

"Only when going straight all four wheels are turning at the same speed rate (or at least about the same rate. I'll add a separate page to explain the exceptions)

 

As soon as a turn is initiated all four wheels will rotate at different rates since each of them follows a different imaginary circle.

This is what happens during a turn:

 

The inside wheels will rotate with less rpm than the outside wheels.

 

The differential on the rear axle guarantees that the rpm delivered via drive shaft from the transfer case are distributed to the left and right wheel as needed. Meaning equal rpm when traveling straight - less rpm to the inside wheel and more rpm to the outside wheel when in a turn.

 

The differential of the front axle does exactly the same thing.

 

The axle differentials take care of the need for different wheel rpm.

 

Interestingly enough during a turn the front axle needs more rpm than the rear axle. Here is why:

 

The front inside wheel will need more rpm than the rear inside wheel.

 

The front outside wheel will need more rpm than the rear outside wheel.

 

This means that the front wheels need more rpm than the rear wheels in a turn

 

When you add the rpm of front wheels (A+B) you will find that the number is higher than the combined rpm of the rear wheels (C+D).

 

Unlike full time 4WD - Part time 4WD is not able to accomodate the need for different axle speeds."

 

http://www.4x4abc.com/4WD101/def_turnfull.html

 

"If you own a vehicle with full time 4WD the need for different rpm front and rear is satisfied by a center differential incorporated inside the transfer case. This third differential, in addition to the two axle differentials, allows the front and rear axles - front and rear drive shafts - to rotate at different rates when needed. Torque and rpm are distributed exactly as needed.

 

Full time systems allow all 4 tires to push or pull at maximum rate. In part time this is not the case.

 

This makes full time systems superior for on-road and off-road use....

 

Full time 4WD: No wind up, no binding, no understeer, no skidding - always maximum pulling power...."

 

http://www.4x4abc.com/4WD101/def_turnpart.html

 

"When traveling with part time 4WD on high traction surfaces like asphalt, concrete, etc. handling of the vehicle will become unsafe (understeer) and the "driveline binding" will eventually cause component failures. Part time 4WD should not be used on high traction surfaces! Even when going straight most of the time, slight differences in tire pressure front to rear or vehicle load resulting in different axle speeds will cause "wind up" and eventually damage."

 

***Assuming that the haldex goes into full lock***

[fzanetti]

Just a good reading article on Audi's new QUATTRO 40/60 split system for the new S series model cars.

 

During this part of the drive I could really feel Audi’s Dynamic Ride Control (DRC) system at work. DRC is a mechanical system, which diagonally links dampers on opposite corners together. The direct effect is that body roll, pitch, and dive is drastically reduced. This was not only apparent when driving the car, but also when comparing the new RS 4 to the old RS 4 out on the track. Through the corners, I was only pushing the car to 8/10, so any effect provided by the new asymmetrical 40/60 quattro differential could not be felt. It is my opinion that it would take 10/10 racetrack driving, or a low traction situation to realize the benefits of the 40/60 quattro versus the former 50/50 system. Neither of those options were available to me.

 

Once reentering the Hockenheimring grounds, I took a slight detour to “play” with the car a little at a large, open parking lot. In a skidpad type test, I gradually increased the cornering speed to get a feel of the car at the limit of adhesion. The amount of grip the new RS 4 generates is quite impressive. However, the “at the limit” handling still leaves room for improvement in my opinion. When the limits are exceeded, you are greeted with safe and dull understeer. Even with the ESP off, I was not able to get the tail out with the new 40/60 differential. One blame factor here is the relative lack of torque compared to the grip available. Another factor lies within the suspension calibration. I feel Audi still has some ways to go if they intend to compete with the driving involvement/experience of the RWD competition. This new RS 4, however, is a step in the right direction and certainly an improvement over a stock B5 RS 4 in terms of suspension.

Soon I’m back at the Audi and quattro GmbH paddock. Like the gentleman before me, I’m back slightly late and I’m not quick to relinquish the keys to the new RS 4. However, the yellow gas pump on the DIS and the 10 km to empty tell me it’s probably time to give it back. On a side note, a totally unscientific gut feeling on the gas mileage tell me the fuel consumption is good given how hard I was driving the car. This is undoubtedly one of the side benefits observed from the FSI injection system. Given the lighter weight and FSI technology, I would be very surprised if the fuel consumption isn’t better than the current S4.

 

 

From:

 

http://www.audiworld.com/features/tests/b7rs42.shtml

 

Flavio Zanetti

Boston, MA

[fzanetti]

Audi AG unveiled in Germany this week a new-generation version of its landmark quattro all-wheel-drive system engineered to impart Audi’s AWD vehicles with handling that more closely replicates that of rear-wheel-drive vehicles. http://subscribers.wardsauto.com/microsites/images/editorial/audi_rs4_05_022505.gifNew quattro system launches with high-performance Audi RS4 in Europe.

 

The new quattro system – launching with the high-performance RS4 sport sedan in Europe – under normal driving conditions “biases” 60% of drive torque to the rear axle and 40% to the front. Since quattro’s inception in 1980, Audi maintained a balanced 50/50 front/rear default torque distribution that it said imparted a high level of security and dynamic stability.

But the traditional 50/50 torque split also imparts quattro-equipped Audis with an inherent and safe understeering handling character that long has been judged dynamically inferior to vehicles – primarily luxury sport sedans – whose rear wheels do 100% of the driving.

Audi engineers, anxious to achieve dynamic parity with its RWD Mercedes and BMW (and now Lexus, Infiniti and Cadillac) rivals, have reengineered the quattro system to send 60% of engine power to the rear wheels, which they say is enough to deliver RWD-like handling while retaining the stable chassis dynamics and all-weather traction ability that were quattro’s original reason for being.

http://subscribers.wardsauto.com/microsites/images/editorial/audi_torsen_differential_05.gifAudi hallmark Torsen center differential reconfigured for rear torque bias.

 

And although the new quattro system debuts for the European RS4 that will not reach North America until 2006, Audi officials here for the launch of the redesigned A4 say U.S. buyers nonetheless will be some of the first to get a taste of the new, rear-biased quattro drivetrain: The ’05 Audi S4, due to hit the U.S. in April, also will be fitted with the new-generation quattro system.

Marc Trahan, Audi of America Inc. director-product management and quality, tells Ward’s the ’05 S4, a 340-hp, 4.2L V-8 equipped variant of the A4 that is a rung lower than the 420-hp RS4, will be the only U.S.-specification Audi to boast the new-generation quattro system until mid-2006, when all ’07 quattro-equipped Audis will be fitted with the new rear-biased architecture.

“The rear-bias (quattro system) fits well into our new, sporty direction (for the Audi brand),” Ulrich Hackenberg, head of concept development and body engineering for Audi AG, tells Ward’s here.

The new quattro system, though changing to the new 40/60 front/rear fixed torque bias for normal dry-road driving, still will retain the quattro design’s primary feature: the ability to apportion the optimum amount of torque between the front and rear axles when wheels lose traction.

The ability to apportion a variable amount of drive torque to either axle in reduced-traction conditions is enabled by the Torsen-design center differential, which has been the heart of the all-mechanical quattro system since Audi adopted the technology in 1987.

 

 

 

Flavio Zanetti

Boston, MA

[IwannaSportSedan]

Sounds like Subie isn't the only one going slightlly rear biased.

 

the 06 WRX STI gets a new rearward-biased center diff. 65% rear, 35% front. with automatic mode (variable torque distribution, similar or same as VTD in the 5EAT transmissions, if I've heard correctly...) and manual control varying from fully locked to full RWD. As well as having a mechanical limited slip mechanism added to speed reaction time, in addition to the electronic control.

 

Damn, I still think that transmission, with a 3.90 or 4.10 final drive would be GREAT in a tuned up Legacy...

 

BTW, the Caddy STS is 60-65% rear biased AWD, too. If I had to buy american, but was not limited by money, I think I could do worse than an STS-V. (I think I like the STS series better than the CTS series, actually... but expensive for what it is.)

[mkaresh]

You guys have got this pretty much covered.

 

Main lesson: if someone is complaining about traction in rain or snow, it's almost always the tires. I have people contact me all the time asking me what car they should buy to correct this problem with their current car. Often I tell them that all they really need are new tires optimized for the conditions they're driving in. Many want a new car anyway. Maybe the rain/snow are just an excuse?

 

Second, that piece about VDC above is the usual marketing/journalistic B.S. that describes a system as something special, when if you look at the words you'll see it's just a description of a generic stability control system. This is what all stability control systems do. Some are more intrusive and/or less precise than others, but the above description is technically generic despite the "unique" language it's clothed in. I see this all the time, and I hate it. It's the same process that heaped lavish praise on the MacPherson Strut for decades.

 

Finally, on the subject of stability control systems, I come across articles, ads, and drivers quite often who talk as if a stability control system affects the feel of a car in typical driving. ("Notice how solid the car feels on the road? That's the beauty of the stability control system at work.") This is far from the truth. Stability control only kicks in when a car is well off its intended path. This doesn't happen 99.9% of the time that your average person is driving a car unless the road is under a couple inches of water or covered in ice. Especially not if the chassis is well-sorted to begin with.

[LegacyTwin]

Wow, didn't realize that this thread had gotten this long, but very interesting views and comments.

[erito]

Real world practice, When driving in snowy/icy conditions, the cars with haldex (some audi, all volvo, vw...) aren't even close to Subaru and Audi Quattro (torsen). All systems that like Haldex need to get the slip before transferring torque get stuck or lose handling before Subaru AWD and Quattro do.

 

Then if you compare handling, you must use the same tires, they have alot to do with the traction.

 

Just my opinion/experience and not scientifically proved

 

Today we have 50cm of fresh snow and counting....

[iyalla]

Finally, on the subject of stability control systems, I come across articles, ads, and drivers quite often who talk as if a stability control system affects the feel of a car in typical driving. ("Notice how solid the car feels on the road? That's the beauty of the stability control system at work.") This is far from the truth. Stability control only kicks in when a car is well off its intended path. This doesn't happen 99.9% of the time that your average person is driving a car unless the road is under a couple inches of water or covered in ice. Especially not if the chassis is well-sorted to begin with.

 

I have to disagree with you there. The stability control systems in current cars a VERY intrusive so much so that the NYTimes did a test in which they gave a bunch of users a test using a plain jane BMW 3 from 1992 against the cars they currently own. One guy had an impreza, another had a Volvo wagon. All their cars came with some for of traction control and stabilty control. They all passed the evasive driving test with flying colors in their cars. They ALL failed in the old Bimmer which had no traction control.

 

The traction systems kick in even in a simple slalom test in dry weather. This even surprised the testers who all thought that their skills were awesome and had nothing to do with the electronics in their cars. The learnt very quickly how much they depended on the systems.

 

Trust me if you have a car with traction control you have NO idea when that thing is kicking in to make you look good! Its not as obvious as ABS. Its subtle. Take the guy who posted here that he took a corner in the snow in his wifes Volvo and it wasn't a problem but then he took his suby on the same corner and oops problem. Subaru all wheel drive without VDC will not save your a$$ when you do something stupid (even if you don't think what you did was stupid) and the rear wheel biased LGT will make you pay dearly.

 

Traction control systems only become very obvious to the driver in stuck situations or of the beaten path because thats when the system is maxing out to keep you going straight BUT most of the time, especially in perfect weather, you will have no clue except, of course, the grin on your face.

 

Right now Subaru with the lower models and LGT are one of the very few only pure all wheel drive cars out there. Enjoy it while you can because VDC is just around the corner.

[ilh]

What a surprise: test someone in an unfamiliar rear-wheel drive car and see how they do compared to their familiar AWD/FWD daily driver. Which do you think they'll do better in? That hardly seems scientific.

[direavenger]

Yeah I hated that article too. They made special note of the Subaru driver doing a complete 360 degree spin in one of the manuevers. Thanks, NYTimes...

[iyalla]

What a surprise: test someone in an unfamiliar rear-wheel drive car and see how they do compared to their familiar AWD/FWD daily driver. Which do you think they'll do better in? That hardly seems scientific.

 

 

Um you're missing the point of the article:icon_roll

Traction contol, Awd and Fwd all help you. Its up to you as the driver to figure their limits out and be carefully especially if you have two types of cars in your driveway or are switching to something new or old.

[fzanetti]

Um you're missing the point of the article:icon_roll

Traction contol, Awd and Fwd all help you. Its up to you as the driver to figure their limits out and be carefully especially if you have two types of cars in your driveway or are switching to something new or old.

 

Exactly....

 

As long as they are not intrusive, limiting your abilities behind the wheel, as some are...

 

Flavio Zanetti

Boston, MA

[jc51373]

Audis suck the big one...Tell ya what, take the wheels off any Audi and put skis on it, because it is nothing short of a SLLLLLLLED.

 

Overpriced, overhyped, ratbox that breaks constantly. Whatever the small differences may be in the AWD systems, I will take my Subie rather than split hairs over the two. Once Audi gets their quality in line with their prices I might consider it. Until then, if I am gonna spend that kind of $$ I will go one step further and buy a 911.

 

Subie is rock solid.

 

 

Just my two cents.

[neelnug]

Trust me if you have a car with traction control you have NO idea when that thing is kicking in to make you look good!

 

A while back my mom had a volvo s80 with stability control. I read up on the technology and decided to give it a test. There is a parking lot nearby with a painted path. I tried to drive as quickly as possible staying within the lines. I tried it again with the stability control turned off. HUGE difference. I demonstrated the same technology by taking a turn way to fast and hard. Stability control brought the car through the turn... with out it I would have had enough oversteer to hit the curb. Evasive action, bad weather, poor driving skills and other unknowns can all be helped immensly with stability control. I was bummed that subaru didnt make it available on the legacy gt.

[mkaresh]

I have to disagree with you there. The stability control systems in current cars a VERY intrusive so much so that the NYTimes did a test in which they gave a bunch of users a test using a plain jane BMW 3 from 1992 against the cars they currently own. One guy had an impreza, another had a Volvo wagon. All their cars came with some for of traction control and stabilty control. They all passed the evasive driving test with flying colors in their cars. They ALL failed in the old Bimmer which had no traction control.

 

The traction systems kick in even in a simple slalom test in dry weather. This even surprised the testers who all thought that their skills were awesome and had nothing to do with the electronics in their cars. The learnt very quickly how much they depended on the systems.

 

I said these systems do not affect the car in "typical driving." Your average driver simulates the conditions of "a simple slalom" roughly never. Or do you live in a unique area that places orange cones in all the parking lots and highways to keep things interesting?

 

Look around the next time you're on the road. Notice how other people are driving? That's "typical driving." The simplest slalom is a relatively extreme condition.

[iyalla]

I said these systems do not affect the car in "typical driving." Your average driver simulates the conditions of "a simple slalom" roughly never. Or do you live in a unique area that places orange cones in all the parking lots and highways to keep things interesting?

 

Look around the next time you're on the road. Notice how other people are driving? That's "typical driving." The simplest slalom is a relatively extreme condition.

 

 

Thats hilarious from someone who lives in Detriot. Maybe you have civilised drivers there. Well in NY and Philly people cut me off all the time, come to a complete stop for no reason all while talking on the cell or something. I have had to use a slalom move a lot of times especially in the wet when these morons come out the most. You must live in a European eutopia in America. Stay there if you can.

 

And I also said even in your so called Typical "Driving Miss Daisy" Driving the stability system is kicking in. You just don't know it unless you have an OBDii scanner on your dash. Every turn you make and stop you make, even in the dry perfect driving conditions of Detriot, are causing the system to kick in.

[ilh]

And I also said even in your so called Typical "Driving Miss Daisy" Driving the stability system is kicking in. You just don't know it unless you have an OBDii scanner on your dash. Every turn you make and stop you make, even in the dry perfect driving conditions of Detriot, are causing the system to kick in.

Every turn and stop? Prove it. That sounds like quite an exageration.

 

I have no problem with it being useful, especially in slippery conditions or emergency maneuvers, but to say it is doing something as you slowly turn into a parking stop is ludicrous.

[2006Specb122]

Can someone please tell me what the maximum amount of power that can be sent front or rear in the legacy 5 speed.

 

I know it is normally 50/50 but I can't seem to find where it hits the max on distribution to front or rear.

 

Thanks

[Garandman]

The best thing about having a debadged H6 Subaru is the look on Audi drivers faces when you go by. Even better that they think it's an H4.

 

Nice interiors, but Konrad hasn't kept up in the reliability department.

[SLegacy99]

I couldnt tell ya the max but the 5 speeds really do run like a FWD car. My front tires are worn significantly more so than the rear.

[ebpda9]

it think the subaru seems worse because of crappy stock tires and shitty shocks. the system can be the best, but if the wheels are not planted firmly on the ground no traction. i noticed my car gets a lot of wind.

[dark_rex]

I couldnt tell ya the max but the 5 speeds really do run like a FWD car. My front tires are worn significantly more so than the rear.

 

 

that's because you turn them. that's what tire rotating is for. judgeing torque distribution by tire wear is completely wrong.

 

dR