DCCD Discussion thread (merged)

[skuttledude]

Paul, excellent article you wrote about the new Subaru STi. I'm guessing the STi will be similar to the one we'll receive here in the states. If there is anyone who hasn't read the article..check it out here: http://www.apexjapan.com/ "Look under Sti..much more than a pretty face"

Since you have driven this fine car and many others too, my question is: How useful is this DCCD to somebody who uses the STi as a daily driver on normal (non raceway) roads?
Personally, I think it would be fun to have a switch that would select the power "bias" front and rear nad hope it comes standard (or at least an option) on the USA STi. But, is it useful?? When would you want it on something other than 50/50? What setting for dry conditions, or wet or snow? What is the true adjustable settings. 10/90 (front rear)? 20/80, 30/70, is 100 rear and 0 front even possible. Could you elaborate on the settings.

Thank you very much for your insights and I look forward to future articles....

BTW, what is your comparison of the EVO 8 vs. STi?

Truly,

Davis

P.S. of course if there is anyone else that has experience of the DCCD feature..fire away!

* Registered users of the site do not see these ads.

[PPower]

BMW system is 40/60 and I understand that the EVO tarmac level puts more power to the rear as well, though I don't know the percentages. More to the rear gives it more of a RWD feel with more safety by putting something to the front. Wouldn't it be nice to have a system like the Skyline where it is RWD until power in front is needed?

[Turboy]

USDM EVO VIII power distribution is 50/50.

[ANZAC_1915]

Generally speaking you'd leave the switch in the Auto position, which allows the torque to shift as needed.

Switching it fully forward is normal for gravel, snow, wet pavement, wet grass.... (John Felstead are you reading?! ) - torque 50% front/rear

Switching it fully rearward for "spirited driving" or the track (dry). - torque ~35/65 front/rear

I have not driven a car equipped with the "auto" position, but it should behave like the current WRX we have (the torque split is not "locked" at 50:50, it "defaults" to that absent different load conditions, and it can shift as required via the center VC).

Switching it fully rearward doesn't make the car an oversteering powersliding monster, but it does alter the "feel".

Paul or John, feel free to jump in here.

Glenn

[zzyzx]

DISCLAIMER for those with interesting imaginations: These general observations assume 1) Relatively sticky dry tarmac is the substrate, and 2) these apply to a steady-state condition. These do not apply to 1) Racing on ice across a lake, or drag racing on ice, 2) Going into a 40 MPH corner at 100, hard braking, followed by lift and steer, etc etc...

The center diff f/r torque distribution will alter the oversteer/understeer balance of the car.

FWD - Full power understeer

RWD - Full power oversteer

AWD 50/50 - same as FWD, full power understeer

AWD 35/65 - or more RWD bias is critical to provide less understeer and more neutral full power balance

Combine AWD 50/50 with a limited slip rear diff and you will always end up in an understeer situation under full throttle.

Does it really matter for commuting? No.

- Steve

[Wombat North]

AH! thanks guys for the info. I posted in the transmission forum and got very little info.
http://forums.nasioc.com/forums/show...hreadid=294792

Seems you get a better response if you post in news and rumors. STI's got everyones attention here

[pio!pio!]

I read in some thread that the DCCD tranny can't take high horsepower applications, so if you are gonna mod a car to high power levels w/ the subaru 6MT, opt for the non DCCD one.

[XT6Wagon]

zzyzx, I can tell you haven't drive a wide variety of cars.

I've gotten power oversteer in FWD cars (hard but very very possible)

Power understeer is the default mode for lots of RWD vehicles.

Oh and a Rear LSD on a RWD/AWD car can make for a very very tail happy car. My bloody subaru wagon on ice swings the tail out to a 35-40 degree angle when launching hard in a STRAIGHT LINE. In the wet power oversteer is all you get. More to the point My old AWD (part time) Topaz with it's std. rear LSD could get oversteer due to the diff, even with the rear driveline NOT GETTING ANY ENGINE POWER! It would "sense" too much slip between the rear wheels in a tight corner and cause the inside to break grip causing the rear to step out a good distance.


Never make geral statements about cars, as they will allways have a notible exception. (in most cases)

[zzyzx]

Ok, then I'd better not comment unless I'm prepared to write a 50 page treatise on chassis dynamics...

If you didn't get the hint from the terse description I gave above, I was generalizing... my bad. My general statements above are probably only good 85-90%.

Of course, I could have written up a 500 word "disclaimer" notice, which includes an "if on ice" section.

For those of you who want to learn this stuff beyond superficial generalizations, then buy a good book like Carroll Smith's "Tune to Win"...

BTW, as to the "default mode" of RWD cars, I've yet to find that toggle switch that says "Give me oversteer".

- Steve

[ANZAC_1915]

The "under power" balance of the car is so dependant on tires, the suspension setup and what you did right before you got on the gas the discussion of it as it relates torque split is pretty moot.

The DCCD is just another variable which can alter the balance of the car.

I expect with the DCCD set forward that (as the split is locked when you set the DCCD out of auto) the car performs better on snow and gravel (if you're a moderately experienced driver). With the stock center VC you can get a "see-sawing" action due to the VC response time (the automatics work faster, both versions).

If you were in a lower grip situation (with the wrong tires) I'd be tempted to use the auto mode though.

I can recall driving RSquire's 22B at Donington that with the DCCD set to fully rear the tail would come out a little under power through the jog into the main straight but the front wheels were still pulling enough to keep it going the right way.

(of course if you lift at the wrong time then no diff setting is going to stop you taking a little spin)

Another thing that will change how the car behaves under power is the front diff (e.g. open, Suretrack), etc.

There is no information on that released yet - interesting the EVO US has an open front diff.

Glenn

[ewt]

I don't know if you saw this, but in another thread Paul talked about DCCD and how good the system is:

2004 Subaru STi

If you pan down to near the bottom there is a detailed description of the feel of DCCD. He mentions that "[he] would gladly pay up to 5k extra on nearly any turbo Subaru to have that system. It works wonders that [he] thought [he'd] have to buy an RWD for. "

It sounds to me that it would be very useful on normal roads-- RWD feel with electronic AWD drive to keep things under control.

Eric

[scott_gunn]

This is kind of off-topic, but I always thought the US WRX would be better off with a front LSD than a rear LSD. On pavement, I never spin the rear tires, it's only the front inside tire that ever spins. As for the rear, either it's sliding or both wheels are gripping.

I can see why the rear LSD would help on gravel or wet roads, but seems a front LSD would be better for most real world (and autocross) situations.

[WRSport]

Hopefully we will be seeing the front diff as well, but somehow I doubt it. We shall know tommorow.

[shirokuma]

Sorry - you are experiencing the twin effects of time zone difference (+16 hours depending on your location!) and recovering from the flu.

The DCCD in automatic setting gave the most transparent feel of AWD I've experienced yet, but I must hasten to add that my entire experience with it was on a track in rather extreme circumstances. Extrapolating that to road driving, I could probably say that for commuting, DCCD-A is unnecessary, but:

It did feel more responsive and, oddly enough, lighter than the standard AWD system. This may have been due to the large difference in engine power and delivery of such between new and older Subaru's.

The main thing to remember is that I'm heavily performance oriented towards mountain-road style driving. For that, the new STi/w DCCD-A is so far the best car I've encountered short of a heavily massaged Miata, and I have to say it felt more balanced than even that Miata, which is saying a hell of a lot.

The GT-R doesn't feel as good. While it theoretically is in RWD mode, the truth is that it's electronics interfere quite quickly, and in a rather obvious way. Then there's it's weight...

Originally posted by pio!pio!
I read in some thread that the DCCD tranny can't take high horsepower applications, so if you are gonna mod a car to high power levels w/ the subaru 6MT, opt for the non DCCD one.

Now, it comes in a car that's making 300+hp and 285ft/lb's of torque - that's a rather high-power application right there. As far as power levels far in excess of that, I have no comment -the car has only been out for a short period of time in Japan, I don't see how the tuners have tested it out thoroughly already.

Cheers,

Paul Hansen

[skuttledude]

Thanks everybody for defining some aspects of the DCCD.
Paul, hope you feel better..the flu just plain sucks! Thankstoo for your hands on details of the DCCD and the STi. Very well written article Its a pleasure to have you posting here.
I suppose we'll know tomorrow if we will see the DCCD on the STi.
Most of my driving is on tight twisty (50-60mph avg.) hilly/mountain roads so I was especially interested in the DCCD. Of course, the weather here in Ohio changes from sun/rain/sleet/snow all the time so AWD is so much fun and hopefully the DCCD will just add to that.

If its an option, I'll take it..thank you very much.

Cheers,

Davis

[EJ20WRX]

Originally posted by Turboy
USDM EVO VIII power distribution is 50/50.

Actually its more liek 60%/40%

[ANZAC_1915]

Bzzzzt: 50/50.

http://mitsubishicars.com/MMSA/jsp/evo/tech.jsp

[Fido]

I've had a lot of questions about the DCCD, like how to use it, when to use what, what happens when you use it, etc. This thread from our friends in the UK helps a lot (http://www.scoobynet.co.uk/bbs/threa...=143750&Page=1), but still leaves me with some questions. Exactly what will happen (not mechanically, I understand that ) if I switch it to full lock and drive around. Sure, I'll get shudder, noise, and some scruffing at low speeds, but what happens if I try a hairpin at a good clip? When would you all use the different degrees of lock (bearing in mind that I think it's infinitely variable, using the 6 position display as a reference)? There's a diff oil temp light, so under what condition could I make that warning light go on? Full lock and a day of driving, or what?

I'm just anxiously awaiting summer so I can get my grubby little hands on my STi

[DistantTea]

Until subaru gives out some sort of "The Complete Idiots Guide to DCCD" I'm completely lost. I know its an Active center diff and from what apex japan said it does have automatic settings. I'm only assuming it has a feature to operate as an open differential when the handbrake is pulled... otherwise they wouldn't have the handbrake suggestions in the short manual.

I can't wait until someone who really knows how to drive these cars sits down and starts describing the system in detail. Maybe a Karl Schielble or Ramman Lackeman (ok I just murdered that dude's name but they're both scca pro rally subaru drivers).

I have a feeling that after break-in its going to take me a month just to figure out what to do and when for performance driving on this thing.

-Tom

[AKGC8]

I'm sure johnfelstead can answer this if he runs across it.

[Fido]

Yeah, John wrote a lot of good informational stuff in the scoobynet post, but he didn't really get into situational driving and the what if's that I'm really curious about

[ANZAC_1915]

The DCCD system on the new car is different from the DCCD on the older gray market STi's in the UK right now.

[RA29]

If set to say, 40% front and 60% rear, will it still transfer power between the front/rear wheels if they slip?
Will it transfer itself to 10/90% for example?

Thanks

[ciper]

Some of you may be helped by researching the Torquemada, it was a DCCD grown from the i-club members. Still in development.

[Jason Saini]

The way I have read it in my research is that in diff free mode it's 35% front, 65% rear as it's normal open bias. Open diffs still can be designed to have a bias, and that's this one's natural bias. Then, by actuating the DCCD you are basically making it a tighter and tighter LSD, all the way up to full lock which would be 50% front, 50% rear mechanical coupling.

The diff never actually mechanically transfers power to ther rear wheels, that's just the diffs natural bias. That means that even in diff free mode, the car will behave more like a RWD car than a FWD one, and you can manually make it tighter.

At half the adjustment range, for example, you will be at around 50% lock for the LSD portion of the diff... This means that the fronts would have to unload WAY more than normal to make them lose traction. So it's more apt to stay with it's natural 35f/65r bias.

With the diff free, if the front tires were on ice and the rears on concrete it would spin the front tires. But all load being equal, it will put more power to the rear tires. And, by adjusting the DCCD, you will reduce this tendency...

It's a bit of a vague concept, but think of the above situation with the front tires on ice....
With diff free, the front wheels will spin...
With DCCD at let's say 10%, you will slowly pull forward off the ice patch, and as soon as the tires are off the ice, the power would go back to 35/65.
With DCCD at 75%, you would quickly move off the ice and resume natural bias.
With DCCD at full lock, you would shoot off the ice.

So the system basically controls how quickly the car can compensate for dissimilar grip or loads.

At least that's my understanding so far...


-Jason Saini
www.over6racing.com www.kingmotorsports.com