Edmunds dealer partner, Bayway Leasing, is now offering transparent lease deals via these forums. Click here to see the latest vehicles!
Options
Subaru Impreza WRX
This discussion has been closed.
Popular New Cars
Popular Used Sedans
Popular Used SUVs
Popular Used Pickup Trucks
Popular Used Hatchbacks
Popular Used Minivans
Popular Used Coupes
Popular Used Wagons
Comments
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
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
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.
-mike
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).
-mike
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
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.
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
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
Later...AH
-mike
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.
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
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
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)
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
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
DjB
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
Later...AH
-Dennis
"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.
-mike
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?
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
-mike
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.
I understand your point and agree with you, unfortunately it's a likely reality.
-mike
Patti
-mike
EVO II? :-)
wannawrx - I've heard summer. Maybe around July or August.
-Dennis
Thanks in advance,
Matt
Stephen
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
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
- Hutch
Later...AH
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.
http://www.sportcompactcarweb.com/archives/technobabble/techno_0402.shtml
Stephen
Bob
-B