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      05-26-2015, 06:29 PM   #1
X135iM
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Performance Control

Just adding my $.02 on this.. never really found anywhere to test/notice any advantage to this system but a new commute of mine leads me to a very long and pretty high speed off ramp... I have tried putting the car to its limits and I find that under heavy acceleration at a decent speed the rear will feel like it is trying to slide out, but it never does (not oversteer) but just the "feeling" of this, like you're almost driving diagonal with no slipping. I am suspecting this is the system braking the inner rear wheel and applying power to the rear axle. Any experience on this?
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      05-27-2015, 06:59 AM   #2
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I think you're describing the yaw control or "brake vectoring" kicking in. Personally, when hustling the car, I can't stand it...

But it does do the job of fending off understeer/tucking the nose of the car when approaching the limits of traction in generally low-speed turns. And yes, it's grabbing brakes on one or more inside wheels.

But it was open diffs and thus no way to actually transfer torque side to side on a given axle.
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      05-27-2015, 07:45 AM   #3
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Installing a Wavetrac limited slip differential on the rear axle was the best mod I have done to my car.
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      05-27-2015, 11:03 AM   #4
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Hi,

I took the Perf. Control on my X1 but did not have the time to test it yet (still breaking in the engine).

I talked rapidly about it in this post:
http://e84.xbimmers.com/forums/showthread.php?t=1128327

I think what you're describing is due to the flex of your rear axle bushings.

I'll coment more when I have time.

Cheers.
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      05-27-2015, 11:13 AM   #5
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Quote:
Originally Posted by PrematureApex View Post

But it was open diffs and thus no way to actually transfer torque side to side on a given axle.
That's one of the functions of the DSC. It will slow down one wheel so power is transferred to the opposite wheel. That's practical on snow when limited grip is available as it won't react to a torque difference, but to a speed difference between oposite wheels of the same axle.
It is this feature that perf. Control uses to "accelerate" the desired wheels in a corner.
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      05-27-2015, 01:45 PM   #6
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Quote:
Originally Posted by paradoxical3 View Post
Installing a Wavetrac limited slip differential on the rear axle was the best mod I have done to my car.
Can you link me towards the product?
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      05-27-2015, 02:33 PM   #7
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Quote:
Originally Posted by NTTY View Post
That's one of the functions of the DSC. It will slow down one wheel so power is transferred to the opposite wheel.
No, it's not. It slows down the inside wheel to induce yaw.

Again, it's an open diff. Torque output at each side of an open diff will ALWAYS be 50/50. Always, by the very definition of an open diff. Some of that power is being eaten by the brake, but there is no "transfer" of anything. An open diff has no mechanism to do anything but 50/50 at all time.

I guess you can say that the faster spinning wheel is putting more power to the ground (by its increased speed vs. the other side), but nothing is transferred via the diff.



When a car with an open diff is stuck in the snow, and one wheel is spinning while the other one is still...

People incorrectly think it's because all the torque is being "dumped" on the wheel with no traction. But that is incorrect. Even in that instance, both wheels are receiving the same torque. What is actually happening is that the torque output is limited by how much torque it takes to spin the wheel with the least traction. the other wheel receives the exact same amount of torque. However, because it has more traction, the torque it does receive is not enough to rotate it and move the car. So it sits there, still.

That's how an e-diff works. Apply the brake on the slipping wheel, upping the torque that side of the diff is "taking", and correspondingly increasing the torque provided to the other side (again, always 50/50). Once it's high enough to begin to rotate the wheel with the traction, away you go.

Last edited by PrematureApex; 05-27-2015 at 02:43 PM..
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      05-27-2015, 03:18 PM   #8
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Here's a better video...



Should be mandatory watching in order to join any car forum!
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      05-27-2015, 04:40 PM   #9
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Not sure what you tried to demonstrate. I did not say there was torque transfer because there's none.
Second part of your second video talks about what I tried to explain. Lock one wheel on the open diff, and the opposite wheel will go faster, while torque remains the same between the two wheels.
So it is not only to induce yaw that one wheel will be slown down, but also to accelerate the opposite one, torque still being split 50/50.

EDIT: Note that Performance Control will brake only the inner rear wheel in a corner, and this is compensated at the same time by an intervention in the engine. And or course, as I said before, slowing the inner rear wheel will make the outer wheel go faster since it is an open differential.

I also checked my user's manual, but it does not answer one question I have. I wanted to know, when deactivating DTC and DSC at the same time, if it would keep Performance Control on, I guess yes but can't be sure. I'll try to test as soon as possible.
Also, the documentation suggests that e-diff is active even if DTC and DSC are deactivated and that it will use brakes to mimic an auto-locking differential on "all driven wheels".
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Last edited by NTTY; 05-28-2015 at 05:22 AM..
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      05-27-2015, 11:03 PM   #10
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Quote:
Originally Posted by dirtye84 View Post
Can you link me towards the product?
http://www.evolutionracewerks.com/node/90

Again, it's the best mod I have ever done.

The open diff sucks on the track, unless you like the car killing the drive out of corners and prematurely wearing tires and brake pads.
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      05-28-2015, 12:58 AM   #11
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Yeah, even my s28i does that slight wiggle when full throttle at low speed on slick pavement.

And I have 255/40r18 Pirelli P7's.

Running without DSC won't work on track since the left rear wheel will spin wildly, and that's coming out of right hand turn even.
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      05-28-2015, 07:41 AM   #12
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Quote:
Originally Posted by NTTY View Post
Not sure what you tried to demonstrate. I did not say there was torque transfer because there's none.
Second part of your second video talks about what I tried to explain. Lock one wheel on the open diff, and the opposite wheel will go faster, while torque remains the same between the two wheels.
So it is not only to induce yaw that one wheel will be slown down, but also to accelerate the opposite one, torque still being split 50/50.
Sorry, guess I misinterpreted when you said "transferred" in response to my comment on the open diff (as nothing is transferred). Sure, there's a difference between the power put to the ground by the wheels , but, as you said, that doesn't have anything to do with varying/transferring torque over the diff.

Anyway, we're on the same page now!

Last edited by PrematureApex; 05-28-2015 at 07:49 AM..
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      06-20-2015, 11:40 AM   #13
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Sorry I've been busy for the last 3 weeks. Yes, indeed, on the same page ;-)
I did 3'000 miles with the car now and so had plenty of time to test.
Perf. control is not active when DSC is completely off. You can feel Perf. Control interventions when in a tight corner (ABS like interventions on one wheel), it indeed allows the car to turn faster, but only when you are accelerating, it obviously does not intervene when braking.
Cheers
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