love the thread guys, lots of information here...

The attesa awd system is the best, but the evo's awd system is the second best, theres only one flaw in the evo's awd system, and thats the 100:0 torque split. If the evo had a 0:100 torque split like the attessa, then it would easily be the best awd system. There is this misconception that the subaru has the superior awd system. While it is a great awd system, and also a true awd system, it is not the best handling awd system available. Bottomline...when you have torque applied to more wheels, you get more understeer.

Because the subaru's dccd transfers torque 50:50 and 35:65 and runs with limited slip, all 4 wheels have torque applied to them at all times which leads to tons of understeer...this is obviously not good for handling. The evo on the other hand can transfer torque 100:0 if necessary, and SAYC can transfer all the torque to the outer front wheel making it "one wheel drive" which is great in terms of handling. Again, the only flaw is that the torque split is 100:0 and not 0:100.

Now, the reason why the sti outhandles the evo in dirt, etc is because its better to have understeer in these situations. When rallier's drive, they rally drift and it is easier to drift in cars that understeer than on cars that oversteer. If you dont believe me watch the drift bible, the ae86 is known as the best drift car and it is a car that understeers.

To sum it up, the true awd systems (ones that always have 4 wheels spinning) can never be superior in terms of handling in normal (tarmac) situations. They can however be superior in wrc situations. The question "which awd system is superior?" is actually a very vague question because it depends on the context of the question. The awd systems such as the evo and attesa are superior for normal situations (and thus superior for us, since 99% of us dont rally), but the true awd systems are most likely better in wrc situations. Let me know if you disagree with my assessment, id love to learn more from this thread.

 

The evo actually can never do 100:0 torque split either. It is similar to the DCCD except that the mechanical diff is set to a 50:50 bias. The electronic component of the ACD just manages the locking of the diff. It's a common misconception that the ACD can completely disengage the rear axle. The subaru diff when open splits 35:65 (I believe the 06 STI has 40:60) and is incompatible with mechanical speed based LSD devices like a VCU. The DCCD locks the diff which makes the torque split go 50:50.

 

if someone can host it, i'll send it. i have like GAZZILLION videos from top gear, BM, rally compilations...waaayy too many

 

The only thing i disagree with you is your conception of torque and why the STi understeers when pushed. Your understanding of torque transfer and its affect on understeer/oversteer is kind of contradictory and confusing. I'm not trying to rip on you, maybe I'm just reading you wrong. You are right that a 0:100 split (all torque going to the rear wheels) would be ideal for best handling, but then you go on to say that the SAYC transfers all the torque to the front outside wheel and that this is great for handling. This completely contradictory. A RWD biased car that oversteers but can be controlled can be driven much faster through and out of a turn by a competent driver. A car with all the torque going to the front outside wheel, the wheel that is carrying most of the turning load and actually making the car turn, will understeer.

Your statement that when you have torque applied to more wheels, you have more understeer. This is like saying that a FWD car with an open differential will outhandle a FWD car with an LSD. A FWD car with all the torque going to one wheel will understeer much more than a FWD car with an LSD that puts power to both wheels proportionally based on the amount of slip that each wheels is experiencing. I think i understand what you were trying to say that a RWD car will understeer less than a similarly set up AWD car. But there are so many variables to take into account: weight, weight distribution, suspension design and settings, tire track, wheel base, etc. Thats why an Evo outhandles a Mustang. And understeer isn't necessarily a bad thing.

99.9% of drivers are not competent enough to handle oversteer and too much oversteer is just plain bad. The reason they made the stock STi understeer is the same reason they make most cars understeer and one of the reasons there are FWD cars: engineers know that understeer is easier to control especially for the average driver. This carries over into your drifting and rally reference and SAYC. Drifting is all about control. Rallying is maintaining control under high speeds in unpredicatble situations and condtions. As already stated, understeer is easier to control than oversteer.

SAYC is not meant to make the car handle better as much as it is to make the car easier to handle, making the driver feel more competent and able to push the car to its limits while still maintaining control. SAYC makes the car easier to handle more than it actually makes the car handle better. Simply put, it makes the car predictable at its limits. It makes the driver faster but not so much the car. The potential was already there, SAYC just helps the driver realize more of it.

Back to the STi... 35:65 torque split should oversteer but reason that the stock STi understeers when pushed to the limit is because of the suspension setup used. So you are correct in stating that handling stock for stock, the Evo AWD system is superior to the STi AWD system. But, a thicker rear sway bar and an anti-lift kit is all it takes to make the STi oversteer in a controlled manner when pushed and handle better than the Evo.

Just because there is some torque to the front wheels does not mean the car will understeer. The rear wheels recieve more torque. It is this difference in potential that makes the car oversteer. And it is because the front wheels still have torque and incite some understeer potential that make a properly set up AWD system predictable when at the limits.

In AWD, you get some of the predictability of FWD and some of the handling ability of RWD combined. Obviously because you are combining them, both aspects will suffer some loss. But you can vary between more predictablility or more handling.

And we haven't even touched on LSDs and their effects on understeer/oversteer. Perhaps another time...

This isn't meant to be a flame because, for the most part, you are correct, AWD is great for what it is: predictablility in less than ideal situations. Especially when the less than ideal situation is who is driving the car.

 

i agree with that. pro drifters set cars that have ~1000hp to understeer as well, allows for more control under greater angles of drift and higher speed, without spinning out. they use wings in the rear as well to provide rear grip which facilitates control at high speed drifts. in GT4 i also like to set my rally cars for some understeer which makes them more controllable under heavy throttle.
now as far as evo goes, eventhough it's more FWD biased initially, i've gotten the back end out on several occasions at lower speeds and poweroversteer (on asphalt), and this is with my '04 that doesn't even have front LSD to tuck the front in under throttle.

 

great analysis...i guess i was somewhat wrong with my thinking, thanks for clearing it up for me

 

because a multiclutch electronically controlled center diff is faster reacting and more variable.

this is the real reason that the radius sucks. if you stick bigger wheels on the car regardless of offset the radius will be more or less the same. a longer wheel base will only make your radius suck as much as the length of the car, ours sucks much worse cuz we have a short car with a ****ty radius. the transverse engine has nothing to do with it, the nsx has similar steering yet it's engine is not only in the rear but also longitudinally mounted.

the reason is because we not only have a fast ratio rack but it's also high sensitivity, hence the magnicficent feel. you can have a fast ratio rack that turns more but you're gonna get a lotta choppyness think ford taurus. if you have a fast ratio and very fine increments then you're not gonna get as much wheel angle but you'll get a great sports steering system.

but that's all you need... you never need to move the front side to side if you have the proper mechanical diff... the torque biasing will do it itself.

my opinion is that the honda and nissan systems may be the most advanced... but the evo's system is the best. firstly because atessa is not even an all wheels drive system, it's a rear wheel drive system that give you awd when you're in need of it. this is already not gonna give you lots of characteristics that we want to see in awd cars. where does honda use it's all wheel drive? (just wondering)

everyone only knows of rally as WRC... wrc is not the only place where rally racing exists... the evos do very well in other groups. wrc is a factory big boy battle, that means more money means more wins. the french companies have so much poured into this they've have two cars racing for the same team... that means two times the help for team points. hardly justification of their awd system. not to say they suck... they're badass but they're also more rich than the other teams.

and this is the sad thing, wrc is one of the few factory big boy competitions where all the big boys aren't big... WHY? cuz rally support sucks, the fans love it, the drivers love it, the workers love it, but someone is skimping us dammit! GIVE US WHAT WE WANT!!!! MORE RALLY!

for what it's worth, the focus wrc is doing very well in the last two years... no one has mentioned ford's awd system.

what you fail to realize is that the signal skyline is also carbonfiber or if ti's not, i'm wondering how they got it to 2600 pounds... and yes skylines are boats regardless, a 3500 pound car qualifies for a boat.

that must be a jdm weight because the skyline weighs 3500 it has always weighed more than the supra.

doesn't it disengage the center diff when you pull the ebrake?

i don't think they designed ALL the horrible understeer into the sti... part of the understeer comes from the massive anti dive tuned inot the chassis of the car. understeer is impossible to control, you cannot steer in any way when understeering. however in an emergency situation, understeer is more SAFE, becuase it will cause you to plow in a straight line instead of turning and spinning and possibly flipping. it's all basic physics, once you introduce angular momentum the situations gets a lot hairier because you need to damp out the angular momentum as well as the transverse momentum.

you had stated that understeer is easier to control than oversteer... that is not only untrue but only true for a novice. in wrc they choose to oversteer because it's easier to control the car in the unpredictable situations cited. i will concede that understeer makes a car more stable but that's also the definition of understeer practically, where oversteer is the reduction in polar moment stability.

sayc is most assuredly to amke the car faster not the driver. and it's basic phsyics once again, getting more--or rather the RIGHT-- amount of traction to the rear outside wheel will get you the absolute fastest pace around a corner wtihout slipping.

 

How is something untrue but then only true for a novice? Are you calling me a novice? Most car drivers, including yourself, are not professionals, don't kid yourself.

A car that is understeering is much easier to correct than one that is oversteering. you don't need a physics degree to know that, just some driving experience.

 

I've always been partial to the DCCD on the new scoobs or the 4Wheel steering on the GTRs...I can't remember the acronym tho.

 

Super HICAS

 

wait, so the evo doesnt have a 100:0 torque split? i read in many threads and in caranddriver that it can split torque 100:0? And getting back to this point, why did mitsubishi design the evo to do this? What benefits come from a 100:0 torque split?

 

I'm not sure why Honda's SH-AWD is even in this discussion yet. Yes, it sounds great on paper because it can bias any wheel front and rear or side to side, but right now it is only on their heaviest luxo car. They haven't won any accolades with it, nor are their any sports cars with it yet.

I'd have to say the title belongs to Mitsubishi. Nissan's system is great, but stock GT-R's aren't anything to shout about, and only the racing versions were banned so many years ago. Lightly prepared Group N Evos dominate everything else in their class and street Evos handle better then almost every other car they go up against.

 

Watch Top Gear, its a lot better then 5th Gear and is the original UK car show.

 

no, not trying to say anything, if you read what you wrote again the proximity of rally racing to understeer is more controllable is very misleading.

 

ahhhh thank you!