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F10 / F11 (2011 - Current)
The new chapter in the highly successful story of the BMW 5 Series Sedan (F10) and wagon (F11)

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  #1  
Old 09-25-2011, 11:32 AM
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Needsdecaf Needsdecaf is offline
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So I disabled ARS....

Following up on the tail end of this thread, I conducted an experiment that I've been wanting to try for a while. I figured that it deserved a new thread.

Quote:
Originally Posted by DreamCar View Post
Looks like this thread is gonna convert in to whole new debate but would greatly appreciate if some body can shed some more light/feedback on ARS

My thoughts exactly.

ARS Part 1 - Discussion on Anti-Roll

Quote:
Originally Posted by Stealth.Pilot View Post
This is one of the few things Needsdecaf and I disagree on.

Having driven Lexus GS cars with ARS and active suspension, and one with just active suspension but no DRS, I have always found ARS reduces floatiness.

Needsdecaf experience comes from another brand too (maybe Volvo or Acura).

So we are both speculating as far as BMWs go, no one will know until we see a non ARS DHP car hit the lots in a few weeks. However I have faith that BMW as a performance engineering company would only offer ARS as an option if it improved performance handling.
To my knowledge, Lexus GS does not have what BMW terms ARS, which is active anti-roll bars. It only has active shocks. In fact, I don't think anyone else except perhaps Mercedes uses the active anti-roll bars.

ARS isn't necessarily meant to increase performance handling. It's used to create luxury handling, in my mind. Two cases in point: ARS was first introduced on the 7 series. Second, new M5 has DDC (active dampers) but NOT ARS (active anti-roll bars). In fact, I do not believe ARS is even an option on the M5.

Think about what ARS does and what an anti-roll bar does. An anti-roll bar is designed to do what it's name says, prevent roll. It does this by connecting one side of the chassis to the other by a rigid bar that is mounted on links. These links allow the bar to rotate if both of the opposing suspension components move at the same rate (i.e. you hit a speed bump). However if the opposing suspension components do not move at the same rate (i.e. lateral loading from one side to the other) the bar is not free to move and acts as a transverse spring (think the Corvette's rear leaf spring) which resists the outside suspension moving upward by the lateral forces acting on it.

However, this system is far from perfect. If you are driving straight, and your left wheel encounters a bump in the road, the anti-roll bar is not free to rotate, and it transmits motion to the other side of the suspension. Therfore, you experience a "head tossing" motion. There are many other motions where the anti-roll bar isn't countering roll, but instead creating extraneous movements in the suspension.

Now, ARS does two things. First, in steady state forward driving, it de-couples the roll bar from one side to the other. This means that the suspension is free to act completely independently. This offers much more comfort as the extraneous suspension movements are reduced. However, if you start giving even a bit of steering input and corresponding lateral load, the car will roll quite a bit. So this type of setting is desired only when the car is tracking straight ahead.

Second thing that it does is effectively vary the rate of the anti roll bar action. Up to a certain g force level (0.5g, I believe), it will twist the anti-roll bar to resist outside suspension upward movement (i.e. resist the car leaning into the turn). After 0.5g, it starts to relax, letting the car roll so that it feels natural and, as the driver approaches the limit, predictable. Essentially, ARS is acting as a variable anti roll bar from zero (decoupled) to much stiffer than normal (0g to 0.5g) then back to what a normal standard anti roll bar would be (after 0.5g).

In summary, ARS is designed to eliminate the compromise found in selecting anti-roll bar setup. Running a stiffer anti-roll bar is great for handling, but sacrifices ride comfort. Likewise, a thin bar is good for ride, but bad for handling. To me, the ARS is designed to reduce harshness of a sporty roll bar setup, not enhance cornering stiffness of a thin bar.
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Last edited by Needsdecaf; 09-25-2011 at 11:50 AM.
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  #2  
Old 09-25-2011, 11:47 AM
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Part II - ARS in action.

So while Stealth.Pilot is true in saying that ARS reduces "wallowing", that's only true if you define wallowing as excessive roll. To me, there are many other suspension movements that feel unnatural that I consider wallow, not just excessive roll. I have always felt that the car feels a bit "bouncy" encountering certain bump patterns. It does not feel tied down. It can feel, at times, less than BMW-like.

I have always blamed this on two things. First, soft springs required with the active dampers. Second, the active anti-roll bars. So I wanted to drive the car with the ARS disabled.

The requisite fuses are in the trunk fuse box. However, BWM's fuse labeling system leaves a lot to be desired. There's no fuse marked ARS. In fact, each "function" has a number of fuses shown to it, sometimes up to 8 fuses! For instance, there is a pictogram of a shock absorber, with about 6 fuse numbers listed next to it. Then there is a picture of a car with rolling arrows with another 6 or so fuses. Two of the "anti-roll" fuses are not shared with the "shock" fuses, so I pulled those. As expected, I got two errors, but not the ones expected. First was a lack of self-parking. Second was a lack of lane departure warning. Interesting. These systems are REALLY interconnected. By playing with the two fuses (131 and 134) I found that if I left 131 in, I would have everything except self-parking and ARS, with the lane departure warning going away. If I left 131 only in, I got ARS back, and only lost lane departure warning.

I only did about 10 minutes worth of driving with ARS disabled, but I can say that the car is MUCH different. I observed much more of the traditional head toss from a car with standard roll bars, however, it was very tolerable. Moreover, I found that the car had lost quite a bit of the floatniess that I feel in normal driving, even in Sport. Finally, I did not get a chance to really lean on the car, so I cannot compare the amounts of roll in ARS on vs. ARS off.

I plan to run ARS off over the next week and see how the car responds in normal driving. Certainly the differences should be enlightening.

One other thought is that there was still some float in the car even with ARS disabled. I suspect the springs are still pretty soft because when ARS is active, it resists roll that the springs do not need to counter. I would be willing to bet that the spring rates for the 2012 sport car (DDC, no ARS) are different than the 2012 car with DDC and ARS, or the 2011 DHP or M Sport cars.

More observations to come. Thoughts are welcome......
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  #3  
Old 09-25-2011, 12:04 PM
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First of all I laud your experiment. Great initiative and also quite ingenious. I am curious to hear your perspective after a week.

My sense is from the initial experience you describe that it may boil down to taste. I haven't felt so much of the floatiness that you describe in the BMW - but it may be because I am used to ARS from my Lexus. However I hate body roll in corners because for me the most fun I have is how fast I can drive the car through highway-to-highway ramps (I have several on my 15 minute commute) and body roll reduces my enjoyment of cornering.

BTW I am surprised that you say it decouples the sway bar. I would have thought it goes from normal setting (same as non-ARS) to more tightly coupled. If it truly decouples it then I would argue this is bad programming by BMW. Perhaps Dinan can address this when they release their suspension programming for the F10.

Quote:
Originally Posted by Needsdecaf View Post
To my knowledge, Lexus GS does not have what BMW terms ARS, which is active anti-roll bars. It only has active shocks. In fact, I don't think anyone else except perhaps Mercedes uses the active anti-roll bars.
It does. This is a classic case of how the general population fails to give Lexus credit for industry leading engineering. Lexus has APSSS similar to ARS like BMW and Mercedes, but no one else does - not Audi, not Jag. Lexus has something called AVS (active variable suspension) which is equivalent to DHP (variable shocks). But it has a separate option which is rare and only installed on a subset of GS450h and GS460 models called APSSS (Active Power Stabilizer Suspension System) which is an active anti-roll bar which appears to be some sort of contraption in the trunk in the space where the spare tire is supposed to be (the APSS models come with run flats). This is similar to ARS. There's also one in the front but I don't know where.

On the Lexus website it is described thus:
Quote:
Active Power Stabilizer Suspension System (GS 460)
The available system equips the front and rear stabilizer bars with an electronic actuator. Wheel-speed and steering-wheel-angle sensors send information to the system's Electronic Control Unit (ECU), which calculates how much force is needed to help keep the vehicle flat in a turn. The front and rear actuators then torque the stabilizer bars, thus increasing the vehicle's sway resistance. And since this is an electronic system, response time is shortened when compared to conventional hydraulic systems.
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Last edited by Stealth.Pilot; 09-25-2011 at 12:29 PM.
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Old 09-25-2011, 12:54 PM
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Quote:
Originally Posted by Stealth.Pilot View Post

It does. This is a classic case of how the general population fails to give Lexus credit for industry leading engineering. Lexus has APSSS similar to ARS like BMW and Mercedes, but no one else does - not Audi, not Jag. Lexus has something called AVS (active variable suspension) which is equivalent to DHP (variable shocks). But it has a separate option which is rare and only installed on a subset of GS450h and GS460 models called APSSS (Active Power Stabilizer Suspension System) which is an active anti-roll bar which appears to be some sort of contraption in the trunk in the space where the spare tire is supposed to be (the APSS models come with run flats). This is similar to ARS. There's also one in the front but I don't know where.

:
Interesting. Didn't know that and my research didn't show anything up.

Yes, BMW's system completely de-couples the roll bar in the middle during steady state driving.

I, too, do not like excessive roll. This is not what I am feeling and describing as floatiness. The floatiness that I feel is more of an overall up and down pogoing motion. Trust me, I am going for sportier, more tied down, and not less roll resistance.

By the way, what mode do you normally drive in?
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Last edited by Needsdecaf; 09-25-2011 at 12:56 PM.
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  #5  
Old 09-25-2011, 01:45 PM
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I am ordering my 550 next week and I am still on the fence on ARS, so I really appreciate you taking the time to do this. I don't want floaty feeling but didn't think that ARS controlled that at all. Is it possible that piling the fuse impacted something else too?
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Old 09-25-2011, 01:47 PM
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Quote:
Originally Posted by tlr550 View Post
I am ordering my 550 next week and I am still on the fence on ARS, so I really appreciate you taking the time to do this. I don't want floaty feeling but didn't think that ARS controlled that at all. Is it possible that piling the fuse impacted something else too?
Impossible to tell. However, changing modes still effects the ride so it looks like the shocks are still working.

If you're ordering, I'd drive both configurations first.
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Old 09-25-2011, 01:49 PM
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Quote:
Originally Posted by Needsdecaf View Post
Interesting. Didn't know that and my research didn't show anything up.

Yes, BMW's system completely de-couples the roll bar in the middle during steady state driving.

I, too, do not like excessive roll. This is not what I am feeling and describing as floatiness. The floatiness that I feel is more of an overall up and down pogoing motion. Trust me, I am going for sportier, more tied down, and not less roll resistance.

By the way, what mode do you normally drive in?
I don't have my 550i yet (Oct 17 ED), but on my extended test drives I tended to keep the car in Sport+.

I drive the Lexus with Suspension and ECT both set to Sport. You can't turn off the APSSS on Lexus either.
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Old 09-25-2011, 02:14 PM
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How do you actually know ARS is off? Is there a light on the dash? Just curious.
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Old 09-25-2011, 02:35 PM
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I don't think ars makes a car floaty per say. I have not experienced or heard of float from any other BMW with ars including my 2008 E60. It doesn't mean that it doesn't contribute to the float in the F10 since it could be that ars is a bad match to ddc. I.e that ddc is the cause of the float and that ars is less effective in masking it than a passive roll bar would be. It's really difficult to say but since my E60 with ars was free from float and very good suspension wise I'm inclined to blame the long soft springs used with ddc.
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Old 09-25-2011, 03:33 PM
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Quote:
Originally Posted by nealh View Post
How do you actually know ARS is off? Is there a light on the dash? Just curious.
It's very obvious the the ride is different.
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Old 09-25-2011, 03:43 PM
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NeedsDecaf thanks a lot for your insight/// so can i count on this "ARS will soften the harshness of a thick Sway Bar and yet avoid the body roll" ?
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Old 09-25-2011, 04:20 PM
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Erregend Erregend is offline
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Quote:
Originally Posted by Needsdecaf View Post
Yes, BMW's system completely de-couples the roll bar in the middle during steady state driving.
What is your cited reference for this statement and for the statement that it
reduces the twist on the bar as turning increases?

More correctly, the reference for:
"Now, ARS does two things. First, in steady state forward driving, it de-couples the roll bar from one side to the other. This means that the suspension is free to act completely independently. This offers much more comfort as the extraneous suspension movements are reduced. However, if you start giving even a bit of steering input and corresponding lateral load, the car will roll quite a bit. So this type of setting is desired only when the car is tracking straight ahead.

Second thing that it does is effectively vary the rate of the anti roll bar action. Up to a certain g force level (0.5g, I believe), it will twist the anti-roll bar to resist outside suspension upward movement (i.e. resist the car leaning into the turn). After 0.5g, it starts to relax, letting the car roll so that it feels natural and, as the driver approaches the limit, predictable. Essentially, ARS is acting as a variable anti roll bar from zero (decoupled) to much stiffer than normal (0g to 0.5g) then back to what a normal standard anti roll bar would be (after 0.5g)."

Last edited by Erregend; 09-25-2011 at 04:25 PM. Reason: Added full quotation.
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Old 09-25-2011, 04:29 PM
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Quote:
Originally Posted by Erregend View Post
What is your cited reference for this statement and for the statement that it
reduces the twist on the bar as turning increases?

More correctly, the reference for:
"Now, ARS does two things. First, in steady state forward driving, it de-couples the roll bar from one side to the other. This means that the suspension is free to act completely independently. This offers much more comfort as the extraneous suspension movements are reduced. However, if you start giving even a bit of steering input and corresponding lateral load, the car will roll quite a bit. So this type of setting is desired only when the car is tracking straight ahead.

Second thing that it does is effectively vary the rate of the anti roll bar action. Up to a certain g force level (0.5g, I believe), it will twist the anti-roll bar to resist outside suspension upward movement (i.e. resist the car leaning into the turn). After 0.5g, it starts to relax, letting the car roll so that it feels natural and, as the driver approaches the limit, predictable. Essentially, ARS is acting as a variable anti roll bar from zero (decoupled) to much stiffer than normal (0g to 0.5g) then back to what a normal standard anti roll bar would be (after 0.5g)."
Multiple locations I've read throughout the years. The system is not new.

Here is an old one:

http://www.caranddriver.com/reviews/...530i-road_test

Quote:
Originally Posted by CarandDriver
The aluminum suspension is also "active," although to better results. Active roll stabilization, taken from the 7-series and part of the 5's Sport package, can effectively disconnect and reconnect, automatically, the front and rear anti-roll bars. The premise is that in straight-ahead driving anti-roll bars are a hindrance to good ride quality but are critical to good handling. This works. You could quibble with the tuning compromise between ride quality and handling-sharp-edged bumps send a jolt through the body. But any car that corners as flatly as this by all rights should ride like a buckboard. It doesn't. It's fantastic how flat this 3756-pound sedan is able to corner. So fantastic, in fact, that we never realized how fast we were going. Body roll might be an undesirable trait, but it is also a form of feedback indicating speed, and that feedback is absent here. Combined with the odd steering, you get the sensation that once you throw the 5 into a corner, your work is done; the car will drive itself through the corner. It's farther away from you
By the way, that quote is from 2004 about the E60 530, not the F10.

Here is a better link, which quotes ZF as a source....good source, those manufacturers. It also discusses Anti-Roll bars better than I did:

Quote:
Originally Posted by Auto Spectator
ZF's Active Roll Stabilization

Cars tend to lean to one side, or sway in a turn. While the vehicle starts to "dive" on the outer radius of the curve, the inner wheels lose their grip on the road surface. The faster the vehicle, or higher the center of gravity, the more it will sway in a cornering situation. This apparent physical limit at which driving dynamics and enjoyment come to an end for full-size sedans and SUVs is well known, and is something that has disgruntled ZF suspension specialists for a long time.

In an effort to improve directional stability on winding roads, ZF engineers focused on a key suspension component: stabilizers. Attached to the front and rear axles, stabilizers are designed to even out the compression of the springs on the left and right wheels. This operation is purely mechanical. A metal bar connects the left and right wheel suspension. But the question, how hard or soft a conventional stabilizer bar should be, often leads to conflicting opinions among chassis designers. An extremely stiff stabilizer is good for reducing vehicle roll. The disadvantage is that it transfers the suspension response to road surface unevenness on one side to the other side of the vehicle. Additionally, stiffer antiroll bars on the front axle cause the vehicle to understeer.

The ideal solution is an active, variable stabilizer. ZF Sachs has been developing the Active Roll Stabilization (ARS) system since 2001. This system is currently available in BMW models under the name Dynamic Drive and is also used in an SUV. ARS is based on a hydraulic oscillating motor mounted near the center of the stabilizer bar. Activated by sensors and an electronic control, the oscillating motor creates torsion and thus adapts the stabilizer to the driving situation. The result is impressive: with lateral acceleration up to 0.5 g, the system fully compensates body roll. As a result, the vehicle remains absolutely parallel to the road surface. For example, ARS enhances driving dynamics in the highly successful SUV segment. ARS also improves self-steering properties. And this increases steering precision.

Source: ZF
http://www.autospectator.com/cars/au...abilization-zf


Here's what it can do:

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Last edited by Needsdecaf; 09-25-2011 at 04:33 PM.
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Old 09-25-2011, 04:44 PM
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Thanks for the citations.

But, as I read this:"Activated by sensors and an electronic control, the oscillating motor creates torsion and thus adapts the stabilizer to the driving situation. The result is impressive: with lateral acceleration up to 0.5 g, the system fully compensates body roll. As a result, the vehicle remains absolutely parallel to the road surface."
it doesn't say the twist in the bar is reduced after 0.5 g, just that 0.5 g is all it will counter.
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Old 09-25-2011, 04:54 PM
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Quote:
Originally Posted by Erregend View Post
Thanks for the citations.

But, as I read this:"Activated by sensors and an electronic control, the oscillating motor creates torsion and thus adapts the stabilizer to the driving situation. The result is impressive: with lateral acceleration up to 0.5 g, the system fully compensates body roll. As a result, the vehicle remains absolutely parallel to the road surface."
it doesn't say the twist in the bar is reduced after 0.5 g, just that 0.5 g is all it will counter.
Knock yourself out. Hope you have a cuppa joe before you start. Hint - look at the top of page 25.

http://www.bmwmotorsports.org/pdf/e7...%20Systems.pdf

The 0.5 g is an engineering choice. It is designed to permit roll after that so the dynamics don't seem unnatural.
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Old 09-25-2011, 06:32 PM
bobblehead bobblehead is offline
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OP, excellent write up and technical explanation... BMW should hire you as a consultant to better explain to the average consumer as to how some of their technology works in 'Layman' term.

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Old 09-25-2011, 06:37 PM
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Originally Posted by bobblehead View Post
OP, excellent write up and technical explanation... BMW should hire you as a consultant to better explain to the average consumer as to how some of their technology works in 'Layman' term.

Looks like he did a PHD on this ARS thinggy
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Old 09-25-2011, 06:45 PM
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Quote:
Originally Posted by Needsdecaf View Post
Knock yourself out. Hope you have a cuppa joe before you start. Hint - look at the top of page 25.

http://www.bmwmotorsports.org/pdf/e7...%20Systems.pdf

The 0.5 g is an engineering choice. It is designed to permit roll after that so the dynamics don't seem unnatural.
Thanks for the link... Very educational... Would love to see same documents for F10.

I must agree with you that on the E70 the ARS is programmed more for comfort
than for improved performance.

It is programmed to act like a thin anti-roll bar when driving straight ahead or turning
slowly, making the ride smoother and handling neutral.

When turning at faster speeds it acts like a fatter and fatter anti-roll bar with a max
countering force equivalent to the size bar that would hold the car level in a 0.5 g turn.

This size bar allows for body roll at sharper fast turns and allows under-steer to develop
so that inexperienced drivers will sense the approaching limits of adhesion.

It is also programmed to balance the "bar size" in the front and back so
that over-steer does not occur.

Maybe one of the tuners will be able to "race tune" these with the suspension.
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Old 09-25-2011, 08:26 PM
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Quote:
Originally Posted by Needsdecaf View Post
Thanks for the DHP/ARS reference. Very interesting reading. I also found it interesting that on startup the system checks the ARS ID number. I suppose this is to ensure that the software matches the hardware. I don't think you are going to get ARS repaired by your local mechanic.
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Old 09-25-2011, 08:41 PM
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Originally Posted by Needsdecaf View Post
Knock yourself out. Hope you have a cuppa joe before you start. Hint - look at the top of page 25.

http://www.bmwmotorsports.org/pdf/e7...%20Systems.pdf

The 0.5 g is an engineering choice. It is designed to permit roll after that so the dynamics don't seem unnatural.
Great article. Thanks.
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Old 09-26-2011, 04:06 AM
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Originally Posted by Erregend View Post

Maybe one of the tuners will be able to "race tune" these with the suspension.
Alpina has on the B5. Shame we don't get it here. I'd settle for just the suspension tuning!
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Old 09-26-2011, 06:10 AM
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Originally Posted by Needsdecaf View Post
Alpina has on the B5. Shame we don't get it here. I'd settle for just the suspension tuning!
My understanding is that Dinan is working on this.
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Old 09-26-2011, 07:07 AM
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Quote:
Originally Posted by Needsdecaf View Post
Knock yourself out. Hope you have a cuppa joe before you start. Hint - look at the top of page 25.

http://www.bmwmotorsports.org/pdf/e7...%20Systems.pdf

The 0.5 g is an engineering choice. It is designed to permit roll after that so the dynamics don't seem unnatural.
uff ! thats why is so expensive
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Old 09-26-2011, 10:28 AM
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While I applaud your experimentation I find one major fault. What is the default setting an ARS equipped car uses when power is disabled to the system? You do not know if the roll bars are working at all or if they are lighter or heavier than a stock non ARS equipped car. What effects will those variables have on the floatiness of the car? The only way to tell if ARS improves handling or not is to compare to a DHP car without ARS.

I had a suspension malfunction (valve block) that disabled ARS and I found the car downright dangerous! In corners even at low G loads the car leaned like an 80's school bus driven by Steve Mcqueen...
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Old 09-26-2011, 11:21 AM
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Originally Posted by Emilner View Post
While I applaud your experimentation I find one major fault. What is the default setting an ARS equipped car uses when power is disabled to the system? You do not know if the roll bars are working at all or if they are lighter or heavier than a stock non ARS equipped car. What effects will those variables have on the floatiness of the car? The only way to tell if ARS improves handling or not is to compare to a DHP car without ARS.

I had a suspension malfunction (valve block) that disabled ARS and I found the car downright dangerous! In corners even at low G loads the car leaned like an 80's school bus driven by Steve Mcqueen...
Sounds like in your case it got stuck disengaged....

My experiment is just that, an experiement. It's not going to tell you with 100% certainty that a non ARS car is better than one with it. As you said, the default setting may differ than a non-ARS car. Also, the DDC tuning may be different as well as spring rates.

Bottom line is that it's not the way that I'd run the car all the time, but gives you a bit of a peek into the life of a DDC car vs a DDC / ARS car.
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