Subaru Impreza WRX

hunter001 · February 2002

Not to re-hash what has been time and again mentioned and beaten to death, but both the VDC-Outback and the Auto-WRX use the VTD-AWD system. Please go back and read the earlier posts before bringing up this issue again.

The VDC-Outback, in addition to the VTD-AWD system, has a traction/stability control system, which is called as VDC. But it lacks the Limited slip differential in the rear. The Auto-WRX, in keeping up with its sporting intentions, has an LSD in the rear, but does not have the traction/stability control system (which is essentially a luxury-car feature). Given a choice between the stability control or the LSD, I would hands-down prefer the LSD, for a car like the WRX, since any traction that is required would be provided by the kick-[non-permissible content removed] VTD-AWD system and the side to side power transfer would be achieved by the LSD. The side-to-side power transfer in the stability-control equipped vehicles (VDC) would be achieved by the application of brakes, since it lacks the LSD.

In addition to that, without going into too much detail, the breadth to which torque/power can be transferred in a VTD-AWD system (VDC-Outback and Auto-WRX), and speed at which it can be transferred is way more than the other AWD systems that Subaru uses. Which is the reason why, vehicles equipped with the VTD-AWD system are a few thousand dollars more expensive than their "other-system-equipped" counterparts. If needed, I can go into further detail. Let me know.

Incidentally, the only other vehicle equipped with VTD in the world is the Twin-turbo Legacy, where the default torque split is set at 30/70 front/rear by varying the pitch of the Torque-sensing planetary gear center differential (which the other AWD systems - VC & other Auto-Subarus - lack).

Later...AH

hunter001 · February 2002

It sounds like what they were describing was the VDC on the Legacy Outback VDC. That system uses a VTD, but it also uses a host of sensors including wheel speed indicators, yaw senors, etc to detect wheel slippage and other traction problems. Now if that is what the VDC consists of, and the WRX lacks the VDC system, how is the VTD able to do all these feats that are reserved for the VDC system?

The host of sensors except the "yaw detectors" are present in the VTD-AWD equipped Auto-WRX, including accelerometers, throttle position sensors, 4-wheel speed sensors, gear position sensors and a host of others which I don't recall off-hand. In fact, the VDC (which also has yaw sensors) just uses what is already present in the regular VTD-AWD and other Auto-Subarus and use it in the application of brakes to keep the vehicle moving in a straight line (stability control). It also cuts power to the engine - thus is intrusive - for its traction control system.

But a major lack of the VDC is, the lack of an LSD, which, IMHO, is mandatory in a car with sporting intentions. The Auto-WRX has the best of both worlds - has the VTD-AWD and the LSD.

In fact, the VTD-AWD system is conceptually similar to the Audi Quattro employed by the A8/S8 and other V8 equipped Audis. This is completely different from the Quattro employed by the regular A4/A6 and also that employed in the Audi TT.

How does Subaru manage to sell such a sophisticated system in a reasonably priced car ? I would think it is because they already are using a heavy-duty version of the exact same hardware (Torque-sensing planetary gear and electro-mechanical transfer clutches) in their World Rally cars and does not involve any additional engineering dollars/yen to develop it anew.

Why have they not provided that in the manual-versions of their cars ? I think it is a matter of adaptability and cost. It is better adaptable onto the Auto-versions than the manual-versions, even though the Rally-cars are true-clutch-less-manuals similar to the BMW-SMG.

Later...AH

bull3964 · February 2002

"Incidentally, the only other vehicle equipped with VTD in the world is the Twin-turbo Legacy"

Not true, Subaru's own site says the Outback VDC is equipped with the VTD.

If the VTD has all the other sensors that you indicate, why doesn't the description of the VTD include those sensors when it does for the description of the VDC?

Also, wonder what would be gained from having 4 wheel speed sensors since the AWD system cannot directly affect the torque to each individual wheel. The only thing the center diff does is direct power between the front and rear. If the right front tire is spinning like mad, that slippage will be detected by the drive shaft sensor and then power will be transfered from the front. Knowing that it's the right front tire doesn't change the outcome at all. The VTD cannot transfer power to the left front tire to compensate nor can it apply brakes to the right front tire to stop it's spinning. It can only transfer power to the back wheels where the LSD would take care of side to side slippage, again negating the need for individual wheel speed indicators since the side to side power transfer is done mechanically exactly the way it's done on the MT VC system. It seems to me that indivudal wheel speed indicators are only necessary if you have a system that can apply selective braking to stop wheelspin, which the VTD can't do.

paisan · February 2002

You know they are the ABS sensors right? They don't have multiple sensors to sense the same thing. It all goes to the ECU and the ECU then dispenses the information to the AWD system.

-mike

bull3964 · February 2002

Well, then the MT has the information on individual wheel speed as well, the AWD system just can't take advantage of it. It also seems as thoug the VTD can't really take full advange of that info either. Yes it can see that one wheel is spinning, but the only thing it can do is transfer power away from the front. Meanwhile, the driveshaft sensors are telling it the same thing. The front is slipping and the power needs to be transferred to the rear. There's nothing more the VTD can do, so what does it matter that it's being told to transfer power from the front via a wheel speed sensor rather than a drive shaft sensor?

Since the VTD can't change the speed of indivudal wheels, about the only advange I see for using that information is a possible degree of quickness involved with detecting slipping at the wheel level rather than driveshaft level, a quickness that the VC already has inherently since it's a mechanical system rather than an electronic system (it doesn't have to detect-correct slippage, slippage causes the correction, leaving out the detection part).

paisan · February 2002

takes time to heat up, that is how the VC works. Once the spin hits the Viscous Fluid (Silicone) it heats it up and then transfers power. The time it takes to heat up the fluid is the reaction time. It isn't nearly as quickly as the electronic systems, and as previously mentioned, the computer learns when it will need to move power around, by storing slippage data and shifting the power BEFORE there is wheel slippage.

-mike

bluesubie · February 2002

The TT Legacy AH is referring to is the Japanese market one.

VTD vs. VDC sensors:

VDC = Steering angle, yaw velocity, lateral accel., 4-wheel speed and brake pressure (and more)

VTD = Throttle position, ATF temp sensor, front & rear wheel speed, shift position switch, brake switch, battery voltage and engine speed

That's what I gather from this FHI PDF file:
http://210.101.116.115/fisita/pdf/G347.pdf

In real-world applications, the redistribution of torque (instead of controlling wheelspin) on any of Subaru's AWD systems is enough to keep you out of trouble.

A past issue of drive magazine had a write-up on Subaru AWD vs. traction control a couple of years ago. You could probably research back issues at subaru.com.

-Dennis

bull3964 · February 2002

"The time it takes to heat up the fluid is the reaction time. It isn't nearly as quickly as the electronic systems"

Is there any hard data to prove this? Or is it just popular belief?

Also, how variable IS the electric system. It uses sensor data that must be sampled. Just like digital music, it can't use all the data all the time it only uses small samples. There has to be a sample rate and then tolerances setup in the computer as to what reaction to take depending on what the data says. Meanwhile, since the VC is a simple mechanical system, it truly is continuously variable depending on the amount of slippage.

I'm also curous as to how the system knows to restore power to a certain set of wheels. In the VC, the fluid cools as it stops spinning which allows more power to go to a set of wheels, if in that instant slippage starts again (no matter how little) the fluid heats up and transfer power away. The electronic system doesn't have that advantage. Does it continually try to put more power back and then back off it detects slippage again? If that is a the case, there must be some interval setup in the computer that says "Try to transfer power back to the default distribution". To me it seems that the VC would be more quickly able to return to default power distribution than the AT system since it strives for equilibrium by nature. Meanwhile, the computer has to tell the AT system to try to go back to it's default state, something that can seem to be not 100% full proof.

Notice, I am completely discounting the learning capabilites here because I am talking about unexpected slippage. There's no way a computer can learn that there just happens to be a patch of ice, snow, or gravel in a certain place on the road.

Now I'm not saying the electric clutch is in any way inferior to the VC, just that it advantages are outweighed by it's faults making it basically equal.

bluesubie · February 2002

Adam - I read on someone's personal site that the VC takes a half wheelspin for the silicon to activate. I'll try to find hard data on that.

Judging from your second to last paragraph, I assume that you haven't read the pdf file in the link I posted. ;-)
"... the estimation technology to detect the coefficient of road friction which is the core of the new VTD control, and experimental results of vehicle equipped with this control system are presented.."
(boy, AH will love this)
Btw, check out the Tri-State forum of the i-club.com. There's a huge Scooby event in Southern NJ this Saturday. People from Maine to Maryland will be there.

-Dennis

hunter001 · February 2002

Not true, Subaru's own site says the Outback VDC is equipped with the VTD.

All of us know about that. In fact, in the US, only the Auto-WRX and the VDC-Outback (both of whom costs 1000s of $ more than the models immediately below them) has it, and elsewhere in the world, only the Twin-turbo Legacy has it.

If the VTD has all the other sensors that you indicate, why doesn't the description of the VTD include those sensors when it does for the description of the VDC?

Where did you check for this "description" ? If it is the Subaru website, it is notorious for not containing anything deep or technical. Also, I think Subaru should publicise the effectiveness of the VTD-AWD (for both nasty weather conditions and also handling) a lot more than they are doing right now. In fact, I have a feeling that they are keeping it real quiet, for fear that the knowledge would scavenge sales from other Subaru models, as I am sure it would.

Later...AH

hunter001 · February 2002

Thanks for the link ! That was really good.

Later...AH

paisan · February 2002

I believe it samples at 10ms intervals, I know that is what the ECU does on the TOD on my Isuzu, I'm pretty sure that the subaru ECU does it in similar refresh rate. I think that is faster than the VC can react, not that the VC system is slow per-say or bad, just more reactionary than the AT systems.

-mike

bull3964 · February 2002

I didn't get a chance to read that link yet, in fact I was typing the previous message before you posted it. I'm at work right now so I won't be able to read it until tonight. I'm still rather foggy on how a system can estimate the friction coeffecient without inducing some wheelspin.

And hunter001, yes I did use subaru's site for that description because I couldn't find any other materials on the web for the information. I do not think that your theory about sales canniblization is correct however.

People buy regular impreza's because they can't afford WRX's (there really is no other reason).

People buy foresters over the VDC outback because they need/want the extra room that it provides. Otherwise the other outback owners most likely simply can't afford the VDC outback (I think the H6 engine is more compelling a reason to buy it than the AWD system).

For years Subaru has marketed the "wheels that slip to the wheels that grip" tirade. I don't know how they could market the VTD any better than that.

One other point before I really have to go for the entire day. What happens in this situation?

The computer learns that you floor it out of curves, therefore always planting the majority of the power to the rear when you exit turns. However, just as you are accelerating this time, you rear wheels encounter a low traction situation (ice, gravel, whatever). Can the system transfer the 90% of power that may have been in the rear (since it learned that it should have 90% in the rear out of turns) faster than the VC can transfer it's default 50% power? Seems as though the system has to be faster because it may have to transfer alot more power quickly.

paisan · February 2002

is only 80/20->40/60
not sure of the VTD variability.

There aren't steering inputs so it would be based on speed/weight/throttle position not steering. (AT system)

-mike

bluesubie · February 2002

The Outback has more room than the Forester. Bad example. :-)
Some people prefer higher displacement over total h.p., so I don't buy your WRX over other Imprezas argument either.

A lot of this speculation would be put to rest if Subaru put out some detailed information on all of the AWD systems. Audi does this (or used to) for the Quattro system. It would probably just lead to more internet AWD arguments anyway. :-)

-Dennis

bull3964 · February 2002

"There aren't steering inputs so it would be based on speed/weight/throttle position not steering. (AT system)"

Still, the point still stands though, the curve was just incidental, it just learns that from going a relitivly lower speed, you step on the throttle to accel quickly and should therefore transfer power to the rear.

I'm also kinda curious if the system changes the default power distrubtion when slippage is detected rather than use the electic clutches to transfer power. For example, in my situation i posted above, would the system keep the default power distribution it assigned for that situation and then manage the power with the clutches or would it change the power distribution and only invoke the use of the clutches on a limted scale?

From what I'm understanding now, the regular AT system can only transfer power though the use of the clutches while the VTD can change the power distribution without the use of the clutches, only using them to react very quickly or to change the power distribution a little from the default. (This may all be talked about in that .pdf that i haven't been able to read yet though)

hunter001 · February 2002

People buy foresters over the VDC outback because they need/want the extra room that it provides. Otherwise the other outback owners most likely simply can't afford the VDC outback (I think the H6 engine is more compelling a reason to buy it than the AWD system).

For your information, there are 2 H6 Outbacks. One of them is the VDC-Outback with the VTD-AWD and the other is the LL Bean-Outback, with the regular-Auto-AWD. The VDC-Outback costs $2400 more than the other H6-equipped LL-Bean Outback.

People who buy the LL-Bean-Outback equipped with the H6 engine, think they are saving thousands by not going for the VDC-Outback. Most buyers, I am sure, are not even aware of the differences and the advantages of the underlying hardware; and the salespersons - who are also equally ignorant - are not helping either. In reality, are the folks who buy the LLBean getting a good deal (by not going for the VDC-Outback ? I don't think so. They are simply getting a different vehicle, at a different price-point, that incidentally share the body and an engine with the other vehicle. 2 different AWD-hardware, 2 different price-points. Is Subaru really doing its part in trying to explain why they are charging that $2400 extra for the VDC-Outback over the LL-Bean-Outback ? Are they really explaining the differences in the underlying hardware ? Nope !! Except for some brief marketing statements, that make absolutely no difference.

When people buy the Auto-WRX over the Auto-RS, they are getting a completely different AWD system, in addition to a turbo-engine and LSD, which is well worth the 1000s of dollars additionally charged for.

Later...AH

edge01 · February 2002

Not to take away from your VDCvsVTC discussion, but has anyone else experienced a great deal of snow/ice build up in the wheel wells and wheels themselves that causes thier WRX to go out of balance and shake like a washing machine on spin cylce?

I've driven my WRX and a friend's 97 Rally Sport and they both have this problem.

Just wondering if this might be a design flaw and if there's anyway to avoid/fix it.

ryan

bruticus · February 2002

does the MT5 also have the LSD? Sorry for sounding like a dunderhead; it's just that I am a dunderhead.

DjB

hunter001 · February 2002

For years Subaru has marketed the "wheels that slip to the wheels that grip" tirade. I don't know how they could market the VTD any better than that.

They are not marketing the VTD specifically by the above slogan. They are marketing the AWD in general. What I meant earlier, is that they should provide more detail about the VTD-AWD and how it rates vis-a-vis the other AWD systems employed by Subaru.

Later...AH

hunter001 · February 2002

Yes, the MT5 has the LSD too. But it shares the same AWD with the RS-MT5. In the Auto-WRX vs Auto-RS, the AWD is also completely different, in addition to the turbo and LSD due to which the premium charged over the Auto-RS is well worth the extra.

Later...AH

bluesubie · February 2002

Some folks here at Edmunds wax the inside of their wheels. This keeps the snow and crud from building up as bad. I get the same thing on my OBS.

-Dennis

bull3964 · February 2002

It seems that all outback models (except the sport) have an LSD.

"H6-3.0 L.L.Bean Edition models have an electronically managed continuously variable transfer clutch and limited-slip rear differential." (the same is true for the other Outback models except sport)

So we have:

2.5RS, 2.5TS, Outback Sport
AT - Active AWD
MT - VC

WRX
AT - VTD + LSD
MT - VC + LSD

Outback (except VDC and Sport)
MT - VC + LSD
AT -Active Awd + LSD

Outback VDC
VTD + VDC

Forester L
AT - Active AWD
MT - VC

Forester S
AT - Active AWD + LSD
MT - VC + LSD

Legacy L Models
AT - Active AWD
MT - VC

Legacy GT Models
AT - Active AWD + LSD
MT - VC + LSD

I wonder who decides (and for what reason) which system goes on which car. I do think the reason why the VDC doesn't have an LSD is because it would interfer with the system.

Personally? I would not buy a VDC model, ever. AWD and power transfer is one thing, engine limiting and automatic braking is another. The later two have no place on a car I drive.

Also, the price difference may also have to do with the 11 speaker mcintosh sound system as well.

paisan · February 2002

Eventually you will have a form of VDC on every car you can get, it's becoming more and more std, like ABS. My guess is over the next 10 years almost all vehicles will have it in one form or another.

-mike

cinosweive · February 2002

I noticed Sport Compact Car included the WRX on their annual list of "eight great cars" for the second year in a row. It appears as though it is their favorite of the eight as well (but maybe that is just my read).

Car and Driver, if I recall correctly, bumped the WRX from their top 10 for the revived T-bird. Now what the hell were they thinking?

dsm6 · February 2002

C and D picked the WRX in their top ten. You are thinking of Motor Trend, who picked the t-bird as their car of the year.

hunter001 · February 2002

AWD and power transfer is one thing, engine limiting and automatic braking is another. The later two have no place on a car I drive.

I agree. In fact, the first version of the VDC did not have a "VDC Off" button but they have added it to the latest version of it. If my car came with a Stability Control system, I would switch it off, if I wanted to do some really aggressive driving. But such systems do have their place, but I personally would not want it, especially due to its intrusive braking and ability to cut engine power.

Given a choice between choosing the VDC(stability system) or an LSD, I would hands-down prefer the LSD, especially on a car like the WRX. But I would not mind having the VDC, in addition to the LSD, as long as it has an "Off" button. At the time of resale, it might win me some points !!

Later...AH

paisan · February 2002

It turns the system back on when you reach 30mph. Mercedes can turn off the ESP system but it only turns off the braking portion and a small % of the throttle control, it will still cut the throttle at some point. I'm not a big fan of these systems myself. Last weekend while in the Pine Barrens http://isuzu-suvs.com/events I had to spin my way out of a mud-pit where I was burried over the frame of the trooper. I just punched it in 2nd gear and it kept bouncing off the rev-limiter but got me through it!

-mike

bull3964 · February 2002

"Eventually you will have a form of VDC on every car you can get, it's becoming more and more std, like ABS. My guess is over the next 10 years almost all vehicles will have it in one form or another."

My god I certantly hope not.

The thing is, it may be a nice thing to have for no brainer driving, but it is not in any way shape for form necessary.

I live in western pa (right now, down near pittsburgh but I went to school north of the snow belt). Aside from REALLY deep snow (8 inches has really been my max), I've driven in just about every weather condition imaginable. And this isn't just with an AWD car, I've done it with three different FWD cars and a RWD van.

You simply do not NEED these intrusive systems. If some want them, fine, but I hope they all come with a way to disable them.

paisan · February 2002

Yep we don't NEED radios, heated seats, power windows, ABS, disc brakes, etc. etc.

I understand your point and agree with you, unfortunately it's a likely reality.

-mike

boaz47 · February 2002

Been looking into getting another car. I can't believe it but a wagon or small SUV seems about right at this time. I went to look at the WRX but it will be too small. The Forrester might fill the bill a bit better. But while looking at the WRX I noticed that there was no way I could get my hand between the valve cover and the inside wheel well. Now just how would I change the spark plugs on a WRX? I remember having to pull a wheel on a old Nova with a 350 to get to the right rear plug but I didn't see an access panel on the WRX. What is the trick?

subaru_team · February 2002

It is tight in there. However, I remember being able to reach in a do it during a technical training class, albeit verrrryyyyy carefully.

Patti

ssoto1 · March 2002

In todays newspaper called the newsday they said the 2003 evo II is coming out with 250 hp next summer so i think the subaru guys are going to do something like wrx si.I'll wait for the SI

paisan · March 2002

Cool a retro car!

-mike

wannawrx · March 2002

When should the new MY of the wrx come out? This fall or winter or what? anyone know?

bluesubie · March 2002

That's WRX STi. ;-)
EVO II? :-)

wannawrx - I've heard summer. Maybe around July or August.

-Dennis

spaceguy · March 2002

I just purchased my 1st car - a 2000 Subaru 2.5RS with an Aftermarket Turbo (HKS). What octane gas should I use?

Thanks in advance,
Matt

barresa62 · March 2002

I would imaging the same octane rating (minimal) as the WRX. That would be a 91 octane rating or premium in most States.

Stephen

nectalover · March 2002

I have read that the WRX is having big problems with how sensitive the ABS works. Is Subaru doing anything about this that anyone knows of? I have heard that while normal breaking if you hit a bump the ABS kicks in and the break drops to the floor and looses breaks for a couple of secs, causing near accidents as people cannot stop in the distance they need. Thanks for any word on this. Late

hunter001 · March 2002

I have never experienced this in my several thousand miles of driving my Auto-WRX. Never ever. The vehicle has always stopped very well, with absolutely no problems whatsoever.

Also, what did you mean by "and the break drops to the floor and looses breaks for a couple of secs," ??

The "brakes drop to the floor " ?? That's news to me !!!

Later...AH

thecat · March 2002

Bill, check over at I-Club.com. There is quite a bit of information on the subject in the "Warranty Issues & SOA Problems" topic. IIRC NTSP is now involved and it's anybody's guess where this is headed.
I experienced the problem once several months ago. I have been unable to replicate it, even on the same road. However, the experience scared me enough that I recently pulled fuse #8 (ABS) and it won't go back in until this issue is resolved. While I'm not recommending that anybody else disable the ABS system, I like the brakes better without ABS.
- Hutch

rex_ruthor · March 2002

Almost caused an accident for me...

edge01 · March 2002

I've also experienced this problem specifically in snowy/ice situations which has nearly thrown me into several accidents. I'm considering pulling the fuse as well until this is figured out.

thecat · March 2002

Ryan - I expect the ABS to activate on snow and ice. In those conditions, ABS doesn't help you to stop shorter but does permit you to maintain control. However, I don't expect ABS to activate on dry roads because of a small irregularity in the road surface. In my case, as apparently with others, the brake dropped and I didn't have any brakes for a second or 2. Seemed like an eternity at the time. Although it hasn't happened since, it's not an experience I want to repeat. Subaru seems to be suffering from cerebral-anal insertion on this issue. I hope they get the problem identified and corrected soon.
- Hutch

nectalover · March 2002

Hunter. I have read on I club, an posted here to see what others were dealing with. Also to get it more press or whatever to try and get it fixed. What I mean by the pedal goes to the floor is that the break pedal inside the car gets forced down to the floor when the ABS gets activated in certain instances. Some say hitting the breaks over railroad tracks sometimes produces it. The main issue I have is hearing that when this rare occurance does happen some people have come close to rolling into busy intersections or plowing into someone from behind, because the break gremlin happened at the exact wrong time then it should. Meaning that the ABS kicked in when it didn't need to be thus throwing the pedal to the floor initiating a loss of breaking power for a few seconds and allowing the car to get down the road that much quicker without breaking power. Sorry for the long post, but I-Club has 14 pages on this and I feel it is a serious problem. I think it what is happening is that the ABS computer or whatever sends the signal that turns on the ABS is confused in certain instances. In those instances it thinks the wheels are locked and therefore is trying to release them, to regain control. When in fact they are already rolling and then continue to roll for longer then is nessesary putting people in harms way as they are getting into close calls with other drivers etc. Just what I know about this situation, and just my 2 cents. Sorry so long once agian. Late

hunter001 · March 2002

I wonder if the VC-AWD (employed by the manual cars) has anything to do with this ?? Quite a few VC-AWD implementations make AWD and the ABS system, operate mutually exclusively. Maybe that is why I have not experienced it, since I am equipped with a different AWD system ?

Later...AH

hazdaz · March 2002

well this is the first that I have heard of this problem, and obvioulsy thats put a little bit `o fear into me (espesially if Hunter is right, and it effects the MT cars). Anyways, cuz of this, I think I'm going to go try out my ABS - in about 2 months time, they have yet to kick-in. I know ABS is loud and kinda unsettling - some systems more than others - so I wanna see how loud the one on our WRX is.
I also would like to say that ABS does not make a car stop sooner (unless were talking about ice/bad road condition). The stopping power of the car is directly related to the size/design of the brakes themselves - not the ABS system.

barresa62 · March 2002

Here's the link posted in Meet The Members section about the design and application of Subaru's ABS as it applies to the WRX. This may answer some questions. BTW, I have experienced this braking issue myself on a couple of occasions. It was kind of scary, especially coming downhill to a stop behind already stopped vehicles. It does take some getting used to but that doesn't mean I like it. This would be one area that is an achilles heel for the WRX, IMO.

http://www.sportcompactcarweb.com/archives/technobabble/techno_0402.shtml

Stephen

rsholland · March 2002

I'm wondering if this WRX-ABS problem is also present with other '02 Imprezas; such as the TS, RS and OBS? Or even Foresters, Legacys and Outbacks?

Bob

beanboy · March 2002

Why would the ABS system be any different on automatic cars? I'd think problems would be worse, since other systems are dependent on the ABS sensors/system...

-B

Subaru Impreza WRX

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