Is ACD the same as DCCD (which varies the locking of the center diff which changes the torque split from 65/35f "open" to 50/50 locked)? or does it do more? Would an aftermarket diff. (Cusco etc.) do a better job (better balance, less understeer) than either adjustable factory system?

 

Nope!! The problem is that if the center diff is stronger (more and faster locking), car will push more

You need to have an open diff to be able to rotate the car and avoid the push. Then the problem with this is that too open center diff wouldn't be the best thing to have in the straight line.

That is the problem with the mechanical diffs and they can be tuned for one thing only and sacrifice the other side. Active diffs can do both and coupled with the steering wheel angle sensor and G sensors readings, it is hard to beat!!

Mr. AWD

 

You would have to spend a tremendous amount of track time tuning the Cusco LSD to get it to work as well as the ACD system and you'll barely see an advantage unless you plan to race.

As far as ACD vs DCCD, I'm sure how DCCD works other than it allows the driver to vary the split anywhere from 50F/50R to 35F/65R or somewhere around there. That split can be locked in place or the system can be placed in auto mode and vary the split while around corners, etc. I'm not sure what inputs DCCD takes in or how it executes compared with ACD. I guess we'll have to wait till it gets here to find out for sure.

Mark

 

I guess what I'm asking is how active is ACD (and DCCD)? MrAWD dosen't a 1way or 1.5 way center diff solve the corner entry understeer problem? I think the car would be awsome with 1 way front and center diffs. Very little understeer and maybe most importaintly... predictable. The problem with most active stuff on a consumer level (remember the active diffs on the WRC cars are FAR more advanced) is that they CAN be tricked in some situations. Simple, predictable, mechanical diffs may be the best choice for budget minded (can't afford WRC stuff!) track users. I agree it's gonna' take a little tuning but I think we can find the balance we need (turn-in, mid-corner, exit) without having to put ACD on the car

 

It stays open the longest in the Tarmac mode. Going down to the Gravel and Snow, just tightens it up more and less slip is available. That is why the car get more "heavy" on dry if you use those settings in there and rear end doesn't want to come around as it should!

As of the DCCD, I am not familiar (yet, I am working on it tough ) with the auto option and what it does. As soon as I figure that out, I will post it somewhere.

From what I know of those 1.5 diffs is that they are just regular tight diffs under the load and more opened when there is none. This wouldn't help you in the middle, since the only fast way trough the turn is at the full throttle!!

For the track use, Cusco units have better usage, but you still run into the problem in the slow corners with a car that has a lot of power which would make it to push more than you would like!

Fedja

 

That is not true (though it is popular fiction!) you can only do that with a low horsepower car on a high grip surface. On any car with moderate to high horsepower that just MAKES understeer (or in low speed corners with RWD it could be oversteer), either way slow. Bottom line: If you can "smack er" down to full throttle at any point in the corner you are going to slow

You were right about the diffs, free on the way in tighter on the way out and you modulate throttle mid-corner too exit to control balance of the car. As long as you've done the entry correctly, the right ammount of driver induced yaw (trail brake) depending on how fast the corner is the rest is pretty easy (as long as you don't mash on the gas!)

I still think the 1 (or 1.5) ways will work maybe better than ACD/AYC. "s own litirature only shows ACD helping free the car up on the entry (just like a 1way would) then AYC helping mid-corner on out (and no one it seams likes AYC on the track because it's weak, heavy and inconsistant). Thoughts?

 

Hmmm, OK let me put it this way then. If your car has an ability to accelerate and you are not using it, then you are not as fast as you could be! The same goes for the corner. If you are not at the full throttle, than you are not going as fast as you could. There are so many good books about this and you could definitely find much more about this, if you feel like.

As of the understeer/oversteer statement, you are even more off. Any car can be tuned to do either of those. There are tendencies that come from the average factory cars, but that can be changed. If your car is tuned that way that full throttle in the turn makes the car to be slightly loose and brings the rear end out, than you could use all of your throttle that is in there. If the car is not tuned than you get what you where referring in the above text.


Fedja

 

O.K. Here we go...If your car is tuned to accept full throttle in the corner and be neutral it is not cornerng as hard as it could. Why? simple physics...load transfer dictates the on the gas the front will be light there fore they do not have as much avaliable grip as the could if the car were balanced therfore your corner speed is slower (even though you are at full throttle). Highest corner speed is all four tires(not just the rear) at optimum slip angle for as much of the corner as possible

The guy who is at full throttle the most for a lap is not always the fastest, it is the guy with the highest average speed for the whole lap! Which means the highest corner speeds (balanced car) which will lead to higher straightaway speeds even if he has to be on the gas later.

Also a car that is tuned to be as loose as you suggest will be very slow on corner entry and even slower through transitions (slaloms, chicanes etc.) and have a slower lap time to show for it. In other words what you are suggesting does help you be on the gas earlier but overall you will be slower. (PM me for credentials or continue, this is good fun )

P.S. I still think the Cusco option will work!

 

Nobody said that you have to apply the full throttle in a violent way and unbalance the car. Then, I am wondering if you have ever seen and M3 or MR2 with inside front wheels 6" up in the air? Or, an AWD with the inside rear wheel up in the air? Or a lots of other car that have tendency to do so under the hard cornering? Higher number of wheel on the ground has nothing to do with higher cornering Gs.

No, the fastest guy is the one who can apply the full throttle earlier than the others. That will give you higher corner exit speed and higher final speed at the end of the straightaway. All of those together will give you higher average speed, which will make you to be the fastest as well.

Also, it is really not that important who has a higher speed at the end of the straightaway. The highest straightaway entry speed is so much more important. The one at the end has a lot to do with the HP and torque numbers of the car and still isn't enough to win. Just think of Lotus Elise vs. Camaro or something else that is on the same page.

I didn't say that car has to be loose as much as you are saying up there. I was saying that it has to be loose enough so you can controllably rotate the rear end under the full throttle. That is so much different than just being loose.

In reference to the slaloms, those are not driven with the full throttle most of the time. Except when they are so open and short that it doesn't effect cars acceleration through the whole section. Most of them are driven with the relatively steady throttle, since even spacing doesn't change requirements between the second opening and the third...

On the other hand, this is where active center diff will be the most helpful on the AWD car and it would be very hard to tune mechanical diff to get the same characteristics.

I did agreed with you on this except for the tight slow turns and high HP numbers. Another thing to have in mind is that activation speed and the locking strength of the active diffs is much higher then the mechanical diffs.

I also find this interesting and unless someone else complains about too much of the whatever, we can do a few more rounds!


Later


Fedja

 

First of all we are about two rounds from agreeing! and this is only about driving on dry (or good grip wet) pavement

I totally agree that the throttle thing, not an on off switch. As far as the MR-2 (used to have a 91 turbo, great car ruined by severe pump cavitation ) and the M-3 and the AWD car each car has different weight distribution therefore "balanced" is a different attitude in each car, it's about getting the appropiate amount of vertical load (for and aft with the brake or gas or trailing throttle)to compensate for centrifugal force which gives you equal slip angles in all the tires (the ones that are on the ground!)
and equates with higher corner speeds. On entry you do want a little more yaw (slip angle in the rear) so you can straighten the wheel out sooner (and therefore get on the gas sooner) which brings me too...

"the sooner you get on the gas (in the corner) the faster you will go" and "exit speed is most important"

Absolutly not. Example: If I stop at the entry I can now be at full throttle through the whole corner but my lap time is obviously slower. So at some point you are balancing entry speed with the point that you will start accelerating. Too slow in and you can get on the gas sooner (but slow). Too fast in too slow at the apex and too late on the gas (slow as well) so what is the best indicator? If you study Telemetry (data acquisition) you will see that the best indicator of lap time is...Apex speed (that's the correct apex without a botched exit). That indicates that again balance through the corner determines lap time not how early you get on the gas. I repeat again the guy that gets on the gas the first in not usually the winner. A good way to understand this is to get familier with the "friction circle." Skip Barber's "Going Faster" is the best at explaing this stuff (I'm guessing you already have it but if you don't you'll love it) .
We're getting there!

 

If you want to stay on the dry, that is fine with me, but the racing principles are still the same. You just have to be even more sensitive to the application of the driving commands!

Well, if you stop at the corner entry, you will be able to go through the whole turn with a full throttle. But, if other driver doesn't stop as you did, but just slows down enough to still be able to apply full throttle through the whole corner, his exit speed is going to be much higher than yours, and repeated corner after corner, his overall time will be better then yours! So, I guess we are pretty much on the same page here!

The apex speed is very important, but if you have to brake right after that (and that would be before the corner exit) due to too much speed, push or what ever else, your exit speed will suffer. So, this is a case which goes against just the apex speed as enough to measure effectives of the particular corner execution.

On the other hand, corner exit speed is not affected by anything else and that is the speed that you are attacking the straight that is ahead of you. The thing is that one who is able to apply the full throttle sooner (assuming it will be able to hold it all the way until the brake point at the end of the straightaway), will have higher exit speed and cover the straight quicker as well.

Almost there!!


Fedja

 

 

Well, that would really depend on the setup your car has, wouldn't it? If your car is setup to oversteer when throttle is applied, than if you do the same you will oversteer. This is generally true for the RWD and some AWD cars. FWD cars would most likely push if you do the same, since they require slightly different technique to drive around the turn.

Also, if you are at the limit of the traction (acceleration or cornering wise) and you try to get more, one end of your car will give up. Now the trick is to tune your car so it will give it up into the right direction, so you wouldn't have to lift to bring it back to the line. That is the beauty of it!!

Fedja

 

What I usually do is to press the QUOTE button on the top of the post that I want to quote and everything shows up surrounded by the proper control strings (like the "(QUOTE)(i)Originally posted by chronohunter (/i)(B)" - but with the angle brackets instead and finish everything with a matching pair of "(/QUOTE)" - note that "/" at the end!). You delete what you don't won't or brake it up with additional sets of the control strings on both sides and insert your comments in between the quoted text!

Hope this helps!


Fedja