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      11-26-2013, 03:33 PM   #1
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What is the weak link in M Adaptive Suspension?

So on my car, there are a few things I notice that bug me about the suspension.

1. Driving over small bumps or train tracks while accelerating unsettles the suspension and the TC light comes on

2. There is a change in pavement material on the freeway near my house and the pavement seems like it's raised about an inch where it changes. When I go over it, the car really hits it hard. Stiff rebound maybe?

3. Going into dips and bigger bumps on the freeway, it feels like the steering goes light a bit. It's just not very confidence inspiring.

All that being said, it's not exactly soft, it's still pretty stiff in sports mode, as you can feel all the little imperfections in the road.

So...what will address these issues? Is it the springs? Dampers? Sway bars? Or is it my rims? I put M3 rims that had +18mm outset in the back and +11mm offset in the front. The fronts are wider so the inside offset is only +1mm out. In the back, they are still 8.5 inch, so they are just pushed out by 18mm. I feel like the bottoming out and steering going light became worse after the rims, but that could be placebo.

Any thoughts from anyone?

Thanks!
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      11-26-2013, 04:30 PM   #2
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Is your new wheel setup lower profile or significantly different weight? Same tires as before? What about psi? If no significant changes, then I doubt any appreciable difference can be attributed to the new wheels...

As for the suspension, I suspect that the weak point is the springs... they seem to be a bit soft overall ,and progressive (softer initially, a little firmer after some travel); maybe optimized more toward the Comfort end of the adaptive range.
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Last edited by DVC; 11-26-2013 at 04:47 PM.
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      11-26-2013, 05:00 PM   #3
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Quote:
Originally Posted by DVC View Post
Is your new wheel setup lower profile or significantly different weight? Same tires as before? What about psi? If no significant changes, then I doubt any appreciable difference can be attributed to the new wheels...

As for the suspension, I suspect that the weak point is the springs... they seem to be a bit soft overall ,and progressive (softer initially, a little firmer after some travel); maybe optimized more toward the Comfort end of the adaptive range.
Weight is about the same. I went from 18 inch 400M to 19 inch M3 forged rims, which have the same weight. And I went from 225 width to 245 width and profile is down from 45 to 35. In the rear, same 255mm width and profile down from 40mm to 35mm
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      11-26-2013, 09:39 PM   #4
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I'm a chassis engineer and I develop adaptive suspensions systems. This will be long.

TLDR:
  • Yes, your wheels and tires will make a difference
  • These systems are very complex, sometimes they do strange things under some outlier road/driving conditions
  • They can't react perfectly to very small/very sharp bumps
  • Requires a really good tuning engineer to fully optimize. Bad tuner = bad ride/handling.
  • There are lots of bad tuning engineers out there.

THE LONG VERSION:


How they work:


These systems (excluding Magnaride) usually work by having passive valves just like any shock absorber, and an active valve in parallel that makes the damping force change.

The ECU has a simulated model of the vehicle including all the suspension parameters (tire stiffness, spring/bushing rates, suspension geometry, wheel/body mass, etc.). Information from various sensors is run through this model to predict what the car is going to do, then the ECU sends a command to the shock, in the form of an electrical current.

When driving down a smooth road, the active valve is fully open, and the damper is in full soft**, or some "steady state" setting close to it. When the sensors detect a large swell, pothole, choppy pavement, etc., or if you turn the steering wheel or brake or whatever, the ECU does the math and sends some current to the active valve solenoid for a split second. The valve gets stiffer, the damping force increases to deal with whatever is going on, then it drops back down to the soft setting. This all happens in fractions of a second.

**(Note that "full soft" is /= comfort mode. Full soft means no current being sent, no active control, absolute minimum damping force. Comfort mode typically has some level of active control, just less of it than normal and sport modes)


Some limitations:

1. Road conditions
Very Small Bumps
Some events, like pavement cracks, roads with a coarse texture, or very small, light undulations, are too small or too fast to detect and/or react to. In these cases, no current command is sent, and the performance will depend on how the full soft mode was tuned. Also, instant response to every road input isn't really ideal either. If the damper reacts to every single tiny bump on the road, it can cause the ride to become busy and jerky. For example . . . Magnaride has much faster response time potential, but they have to put an artificial threshold there anyway to prevent this issue.

Very Sharp Bumps

Larger events that are very sharp, like your pavement transition or a manhole cover, occur too quickly for the damper to react in the ideal manner. Its possible that the full soft mode isn't soft enough for these bumps, but it's more likely that the harshness you feel is actually a result of not enough damping at the instant that you first hit the impact. With lower damping, the tire kicks off the impact rather than enveloping it, and you get more/faster wheel motion than you would if you had more damping. This limitation will affect the body's reaction to the initial kick as well as how the wheel and body settle after the bump. If you bring in more damping faster at the initial impact, you can improve the impact quality on sharp bumps, but again, the ride can get jerky and busy on other types of roads. It's still all a compromise.


2. Adaptability and Hardware
The model in the ECU isn't perfect, and how not-perfect it is depends on many things. One trend now is to reduce the number of sensors on the car to save money. When we're tuning, we have all kinds of high precision accelerometers, height sensors, yaw sensors, GPS, etc. on the car to measure what it's doing. But the production car may only have 4 height sensors to go by, and they may be less precise than we would like. So we have to do some fancy math to know what the car is doing, which means it takes longer and the result is less accurate.

As far as your wheels and tires go:

The difference between your old and new wheels may not seem like much, but in engineering terms, an 18mm offset difference in the rear is HUGE, and will definitely affect the accuracy of the model. Say for example that 18mm equates to a 10% increase in suspension lever arm length. That means the damper will have to make 10% more force in order to get the same level of control as before, but the ECU doesn't know that!. That's before we talk about width, diameter, tire stiffness, scrub radius, etc, etc.

3. Lots of things going on at once

If you hit a pothole in a corner while braking over a large swell, the ECU has to prioritize all those different events to decide what command to send. 1st priority would be to make sure the car is controlled and safe, then to prevent wheel/tire/body damage in the pothole, then other comfort and handling concerns.

4. Complexity of tuning

Semi-active shocks are some of the most complex, non-linear, un-model-able mechanical components on a modern car, and the car is EXTREMELY sensitive to very small changes in their behavior. These systems can cost the OEM up to $1000 or more, which is a big chunk of change for just 4 shocks and some sensors. When we're tuning these things, we make changes on the order of a couple pounds of force, and that results in big changes to the car's behavior.

My point is that these things are very difficult and time consuming to tune, and if the tune isn't robust and the algorithm doesn't properly account for all roads and conditions, the car might do strange things under some circumstances. IMO, only in the past couple years has the hardware, software, and engineering capability come together for semi-active suspensions to be really good. Even then, it depends HEAVILY on the tuning engineers skills and knowledge.

I believe the F30 Adaptive Dampers are made by Tenneco. I haven't driven one of their systems, but from what I know, this system is a bit behind the current state of the art. Sachs has some valve-based systems that are really good, and GM's latest Magnaride cars are really good. Things are advancing pretty rapidly in my field right now, so within the next couple years these systems should be even better.

My Personal Thoughts . . .

All said and done, a GOOD adaptive system can be MUCH better than any passive system if properly tuned. I've heard mixed reviews of the F30 system, and I'm having a hard time finding one locally to test drive. Regardless, I've decided that my next car will have an adaptive system . . . I've just got to find one that meets my high standards. Unfortunately the stuff I'm working on now won't be on the market for a few more years, so I'm kind of stuck hoping the other guys have tuned something that I like.
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      11-27-2013, 01:43 AM   #5
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Quote:
Originally Posted by Racer20
I'm a chassis engineer and I develop adaptive suspensions systems. This will be long.

TLDR:
  • Yes, your wheels and tires will make a difference
  • These systems are very complex, sometimes they do strange things under some outlier road/driving conditions
  • They can't react perfectly to very small/very sharp bumps
  • Requires a really good tuning engineer to fully optimize. Bad tuner = bad ride/handling.
  • There are lots of bad tuning engineers out there.

THE LONG VERSION:


How they work:


These systems (excluding Magnaride) usually work by having passive valves just like any shock absorber, and an active valve in parallel that makes the damping force change.

The ECU has a simulated model of the vehicle including all the suspension parameters (tire stiffness, spring/bushing rates, suspension geometry, wheel/body mass, etc.). Information from various sensors is run through this model to predict what the car is going to do, then the ECU sends a command to the shock, in the form of an electrical current.

When driving down a smooth road, the active valve is fully open, and the damper is in full soft**, or some "steady state" setting close to it. When the sensors detect a large swell, pothole, choppy pavement, etc., or if you turn the steering wheel or brake or whatever, the ECU does the math and sends some current to the active valve solenoid for a split second. The valve gets stiffer, the damping force increases to deal with whatever is going on, then it drops back down to the soft setting. This all happens in fractions of a second.

**(Note that "full soft" is /= comfort mode. Full soft means no current being sent, no active control, absolute minimum damping force. Comfort mode typically has some level of active control, just less of it than normal and sport modes)


Some limitations:

1. Road conditions
Very Small Bumps
Some events, like pavement cracks, roads with a coarse texture, or very small, light undulations, are too small or too fast to detect and/or react to. In these cases, no current command is sent, and the performance will depend on how the full soft mode was tuned. Also, instant response to every road input isn't really ideal either. If the damper reacts to every single tiny bump on the road, it can cause the ride to become busy and jerky. For example . . . Magnaride has much faster response time potential, but they have to put an artificial threshold there anyway to prevent this issue.

Very Sharp Bumps

Larger events that are very sharp, like your pavement transition or a manhole cover, occur too quickly for the damper to react in the ideal manner. Its possible that the full soft mode isn't soft enough for these bumps, but it's more likely that the harshness you feel is actually a result of not enough damping at the instant that you first hit the impact. With lower damping, the tire kicks off the impact rather than enveloping it, and you get more/faster wheel motion than you would if you had more damping. This limitation will affect the body's reaction to the initial kick as well as how the wheel and body settle after the bump. If you bring in more damping faster at the initial impact, you can improve the impact quality on sharp bumps, but again, the ride can get jerky and busy on other types of roads. It's still all a compromise.


2. Adaptability and Hardware
The model in the ECU isn't perfect, and how not-perfect it is depends on many things. One trend now is to reduce the number of sensors on the car to save money. When we're tuning, we have all kinds of high precision accelerometers, height sensors, yaw sensors, GPS, etc. on the car to measure what it's doing. But the production car may only have 4 height sensors to go by, and they may be less precise than we would like. So we have to do some fancy math to know what the car is doing, which means it takes longer and the result is less accurate.

As far as your wheels and tires go:

The difference between your old and new wheels may not seem like much, but in engineering terms, an 18mm offset difference in the rear is HUGE, and will definitely affect the accuracy of the model. Say for example that 18mm equates to a 10% increase in suspension lever arm length. That means the damper will have to make 10% more force in order to get the same level of control as before, but the ECU doesn't know that!. That's before we talk about width, diameter, tire stiffness, scrub radius, etc, etc.

3. Lots of things going on at once

If you hit a pothole in a corner while braking over a large swell, the ECU has to prioritize all those different events to decide what command to send. 1st priority would be to make sure the car is controlled and safe, then to prevent wheel/tire/body damage in the pothole, then other comfort and handling concerns.

4. Complexity of tuning

Semi-active shocks are some of the most complex, non-linear, un-model-able mechanical components on a modern car, and the car is EXTREMELY sensitive to very small changes in their behavior. These systems can cost the OEM up to $1000 or more, which is a big chunk of change for just 4 shocks and some sensors. When we're tuning these things, we make changes on the order of a couple pounds of force, and that results in big changes to the car's behavior.

My point is that these things are very difficult and time consuming to tune, and if the tune isn't robust and the algorithm doesn't properly account for all roads and conditions, the car might do strange things under some circumstances. IMO, only in the past couple years has the hardware, software, and engineering capability come together for semi-active suspensions to be really good. Even then, it depends HEAVILY on the tuning engineers skills and knowledge.

I believe the F30 Adaptive Dampers are made by Tenneco. I haven't driven one of their systems, but from what I know, this system is a bit behind the current state of the art. Sachs has some valve-based systems that are really good, and GM's latest Magnaride cars are really good. Things are advancing pretty rapidly in my field right now, so within the next couple years these systems should be even better.

My Personal Thoughts . . .

All said and done, a GOOD adaptive system can be MUCH better than any passive system if properly tuned. I've heard mixed reviews of the F30 system, and I'm having a hard time finding one locally to test drive. Regardless, I've decided that my next car will have an adaptive system . . . I've just got to find one that meets my high standards. Unfortunately the stuff I'm working on now won't be on the market for a few more years, so I'm kind of stuck hoping the other guys have tuned something that I like.
Excellent explanation! Were the E9X M3's dampers made by Tenneco too?
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      11-27-2013, 04:34 AM   #6
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      11-27-2013, 06:59 AM   #7
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Quote:
Originally Posted by Sedan_Clan View Post
Excellent explanation! Were the E9X M3's dampers made by Tenneco too?
I don't know, but I want to. If someone could take a picture of the solenoid on the side or the label, I might be able to tell. I've driven a couple E92 M3's with that system and I was pretty happy with it, at least during my short drives.
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      11-27-2013, 08:44 AM   #8
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Quote:
Originally Posted by Racer20
Quote:
Originally Posted by Sedan_Clan View Post
Excellent explanation! Were the E9X M3's dampers made by Tenneco too?
I don't know, but I want to. If someone could take a picture of the solenoid on the side or the label, I might be able to tell. I've driven a couple E92 M3's with that system and I was pretty happy with it, at least during my short drives.
I was quite happy with the EDC in that car as well, even when paired with an H&R spring.
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      11-27-2013, 09:45 AM   #9
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Thanks for the input Racer20, great information.
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      11-27-2013, 10:09 AM   #10
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Thanks for posting Racer20 - great info! Looking forward to reading more of your thoughts after you test drive an adaptive F30.
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      11-27-2013, 03:58 PM   #11
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I've driven an M3 with EDC extensively, and it's a completely different feeling from the F30. It may be a similar setup, but the OEM damping for the soft mode and sport mode are very well done, everything feels tight and planted, and handles sharp bumps ALOT better
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      11-27-2013, 04:03 PM   #12
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Quote:
Originally Posted by Racer20 View Post
I'm a chassis engineer and I develop adaptive suspensions systems. This will be long.

TLDR:
  • Yes, your wheels and tires will make a difference
  • These systems are very complex, sometimes they do strange things under some outlier road/driving conditions
  • They can't react perfectly to very small/very sharp bumps
  • Requires a really good tuning engineer to fully optimize. Bad tuner = bad ride/handling.
  • There are lots of bad tuning engineers out there.

THE LONG VERSION:


How they work:


These systems (excluding Magnaride) usually work by having passive valves just like any shock absorber, and an active valve in parallel that makes the damping force change.

The ECU has a simulated model of the vehicle including all the suspension parameters (tire stiffness, spring/bushing rates, suspension geometry, wheel/body mass, etc.). Information from various sensors is run through this model to predict what the car is going to do, then the ECU sends a command to the shock, in the form of an electrical current.

When driving down a smooth road, the active valve is fully open, and the damper is in full soft**, or some "steady state" setting close to it. When the sensors detect a large swell, pothole, choppy pavement, etc., or if you turn the steering wheel or brake or whatever, the ECU does the math and sends some current to the active valve solenoid for a split second. The valve gets stiffer, the damping force increases to deal with whatever is going on, then it drops back down to the soft setting. This all happens in fractions of a second.

**(Note that "full soft" is /= comfort mode. Full soft means no current being sent, no active control, absolute minimum damping force. Comfort mode typically has some level of active control, just less of it than normal and sport modes)


Some limitations:

1. Road conditions
Very Small Bumps
Some events, like pavement cracks, roads with a coarse texture, or very small, light undulations, are too small or too fast to detect and/or react to. In these cases, no current command is sent, and the performance will depend on how the full soft mode was tuned. Also, instant response to every road input isn't really ideal either. If the damper reacts to every single tiny bump on the road, it can cause the ride to become busy and jerky. For example . . . Magnaride has much faster response time potential, but they have to put an artificial threshold there anyway to prevent this issue.

Very Sharp Bumps

Larger events that are very sharp, like your pavement transition or a manhole cover, occur too quickly for the damper to react in the ideal manner. Its possible that the full soft mode isn't soft enough for these bumps, but it's more likely that the harshness you feel is actually a result of not enough damping at the instant that you first hit the impact. With lower damping, the tire kicks off the impact rather than enveloping it, and you get more/faster wheel motion than you would if you had more damping. This limitation will affect the body's reaction to the initial kick as well as how the wheel and body settle after the bump. If you bring in more damping faster at the initial impact, you can improve the impact quality on sharp bumps, but again, the ride can get jerky and busy on other types of roads. It's still all a compromise.


2. Adaptability and Hardware
The model in the ECU isn't perfect, and how not-perfect it is depends on many things. One trend now is to reduce the number of sensors on the car to save money. When we're tuning, we have all kinds of high precision accelerometers, height sensors, yaw sensors, GPS, etc. on the car to measure what it's doing. But the production car may only have 4 height sensors to go by, and they may be less precise than we would like. So we have to do some fancy math to know what the car is doing, which means it takes longer and the result is less accurate.

As far as your wheels and tires go:

The difference between your old and new wheels may not seem like much, but in engineering terms, an 18mm offset difference in the rear is HUGE, and will definitely affect the accuracy of the model. Say for example that 18mm equates to a 10% increase in suspension lever arm length. That means the damper will have to make 10% more force in order to get the same level of control as before, but the ECU doesn't know that!. That's before we talk about width, diameter, tire stiffness, scrub radius, etc, etc.

3. Lots of things going on at once

If you hit a pothole in a corner while braking over a large swell, the ECU has to prioritize all those different events to decide what command to send. 1st priority would be to make sure the car is controlled and safe, then to prevent wheel/tire/body damage in the pothole, then other comfort and handling concerns.

4. Complexity of tuning

Semi-active shocks are some of the most complex, non-linear, un-model-able mechanical components on a modern car, and the car is EXTREMELY sensitive to very small changes in their behavior. These systems can cost the OEM up to $1000 or more, which is a big chunk of change for just 4 shocks and some sensors. When we're tuning these things, we make changes on the order of a couple pounds of force, and that results in big changes to the car's behavior.

My point is that these things are very difficult and time consuming to tune, and if the tune isn't robust and the algorithm doesn't properly account for all roads and conditions, the car might do strange things under some circumstances. IMO, only in the past couple years has the hardware, software, and engineering capability come together for semi-active suspensions to be really good. Even then, it depends HEAVILY on the tuning engineers skills and knowledge.

I believe the F30 Adaptive Dampers are made by Tenneco. I haven't driven one of their systems, but from what I know, this system is a bit behind the current state of the art. Sachs has some valve-based systems that are really good, and GM's latest Magnaride cars are really good. Things are advancing pretty rapidly in my field right now, so within the next couple years these systems should be even better.

My Personal Thoughts . . .

All said and done, a GOOD adaptive system can be MUCH better than any passive system if properly tuned. I've heard mixed reviews of the F30 system, and I'm having a hard time finding one locally to test drive. Regardless, I've decided that my next car will have an adaptive system . . . I've just got to find one that meets my high standards. Unfortunately the stuff I'm working on now won't be on the market for a few more years, so I'm kind of stuck hoping the other guys have tuned something that I like.
Now I know we have an expert in our midst! When you do get an chance to drive an F30 with adaptive suspension, please come back here and update us on your experience! Thanks!!
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      11-27-2013, 05:10 PM   #13
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Quote:
Originally Posted by Sedan_Clan View Post
I was quite happy with the EDC in that car as well, even when paired with an H&R spring.
With a full set of sensors and a good algorithm, it's easier for EDC to accommodate for minor suspension changes. I'm guessing the E92 M3 has a more sophisticated system than the F30.
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      11-27-2013, 05:14 PM   #14
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Quote:
Originally Posted by momo3605 View Post
I've driven an M3 with EDC extensively, and it's a completely different feeling from the F30. It may be a similar setup, but the OEM damping for the soft mode and sport mode are very well done, everything feels tight and planted, and handles sharp bumps ALOT better
I agree. That and the Cadillac ATS are the best semi-active damping cars I've driven. I was pretty impressed with my short stint in a new 650i as well, but I didn't get it on bumpy roads. I've heard the 5 series isn't as good.
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      11-27-2013, 05:15 PM   #15
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Quote:
Originally Posted by momo3605 View Post
Now I know we have an expert in our midst! When you do get an chance to drive an F30 with adaptive suspension, please come back here and update us on your experience! Thanks!!

I will. I've been looking for one to test drive locally for months, but none of the dealers here check that option box for their stock. Everything is xDrive automatic with base suspension.
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      11-27-2013, 05:53 PM   #16
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Quote:
Originally Posted by Racer20 View Post
I will. I've been looking for one to test drive locally for months, but none of the dealers here check that option box for their stock. Everything is xDrive automatic with base suspension.
Yea, I went to like 3 different dealers, and no one had it. So I was like, screw it, it has the words dynamic, M, and sport in the title of the option, so it must be good. Big mistake... I wish I could drive a non adaptive and adaptive back to back
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      11-28-2013, 04:47 PM   #17
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Racer20, what are your thoughts on the claims that a faster lap time can be recorded in an adjustable suspension's Comfort mode than Sport mode? (I've read this claim a few times with various cars - not just BMWs). It seems counter intuitive that a softer suspension (with more body pitch/roll) could maintain better grip and speed...
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      11-28-2013, 06:01 PM   #18
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Quote:
Originally Posted by DVC View Post
Racer20, what are your thoughts on the claims that a faster lap time can be recorded in an adjustable suspension's Comfort mode than Sport mode? (I've read this claim a few times with various cars - not just BMWs). It seems counter intuitive that a softer suspension (with more body pitch/roll) could maintain better grip and speed...
Here's the next chapter:

First, some backgroud

Stiffer and softer aren't really that meaningful when you're talking about a whole suspension system. The reason stiffer is better is that a pair of tires (left and right or front and rear) works better when the weight on them is equal. When you transfer weight between the two, as in body roll, brake dive, or squat, you ALWAYS sacrifice grip.

All else equal, a stiffer suspension resists weight transfer better than a softer one, and less weight transfer means high total traction capacity between all 4 tires.

However, "all else equal" is rarely the case. Some factors that might cause stiffer to be slower:
  • Not enough compliance to maintain grip on a bumpy track
  • Poor front to rear balance (poor steering response or feedback, unbalanced roll, excessive under/oversteer)
  • Non linear, jerky suspension motion or jacking
  • Too responsive for the driver skill, not confidence inspiring. Stiffer suspension means there is less body motion to clue the driver in as to what's going on, and also requires faster reaction times and more precise inputs.

How this relates to the E92 M3:


My understanding is that "sport mode" in an E92 M3 is a fixed steady state setting with no adaptive control. I was surprised when I read this, because you give up the main benefit of EDC when you do this, and this will almost NEVER result in an optimum solution. I can see several of the above scenarios being the case if the shocks are being used in this manner.

The competition package supposedly uses adaptive control for sport mode, which, in theory, should be much better, but I haven't really looked into lap times. The E92 is on my shopping list for my next car, and I would not buy one without ZCP because IMO, the base EDC sport mode is useless. (I haven't driven it in sport, but that's my conclusion based on what I know and the reviews I've read).

Further, keep in mind the Nurburgring is a very unique place, and typically requires quite a bit more body control than our tracks here. A car that is optimized for the 'Ring may be too much for your average driver on an average track here. Plus, tuning on the ring isn't really about lap times, it's about making sure the car handles the various individual corners, bumps, and pavement transitions well.
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      11-29-2013, 02:41 AM   #19
lmaleke
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Lightbulb

Quote:
Originally Posted by Racer20 View Post
Here's the next chapter:

First, some backgroud

Stiffer and softer aren't really that meaningful when you're talking about a whole suspension system. The reason stiffer is better is that a pair of tires (left and right or front and rear) works better when the weight on them is equal. When you transfer weight between the two, as in body roll, brake dive, or squat, you ALWAYS sacrifice grip.

All else equal, a stiffer suspension resists weight transfer better than a softer one, and less weight transfer means high total traction capacity between all 4 tires.

However, "all else equal" is rarely the case. Some factors that might cause stiffer to be slower:
  • Not enough compliance to maintain grip on a bumpy track
  • Poor front to rear balance (poor steering response or feedback, unbalanced roll, excessive under/oversteer)
  • Non linear, jerky suspension motion or jacking
  • Too responsive for the driver skill, not confidence inspiring. Stiffer suspension means there is less body motion to clue the driver in as to what's going on, and also requires faster reaction times and more precise inputs.

How this relates to the E92 M3:


My understanding is that "sport mode" in an E92 M3 is a fixed steady state setting with no adaptive control. I was surprised when I read this, because you give up the main benefit of EDC when you do this, and this will almost NEVER result in an optimum solution. I can see several of the above scenarios being the case if the shocks are being used in this manner.

The competition package supposedly uses adaptive control for sport mode, which, in theory, should be much better, but I haven't really looked into lap times. The E92 is on my shopping list for my next car, and I would not buy one without ZCP because IMO, the base EDC sport mode is useless. (I haven't driven it in sport, but that's my conclusion based on what I know and the reviews I've read).

Further, keep in mind the Nurburgring is a very unique place, and typically requires quite a bit more body control than our tracks here. A car that is optimized for the 'Ring may be too much for your average driver on an average track here. Plus, tuning on the ring isn't really about lap times, it's about making sure the car handles the various individual corners, bumps, and pavement transitions well.
^^^ this dude knows his shiet we need posts like this

Alright, some quick questions.. so in a sense, one would be better of with the stock suspension as replacing one with a set of coilover, be that Ohlins, KW, Bilsteins, Konis, whatever else brands out there, is actually counter productive. Well, the replacement would be beneficial if the new suspension is being properly tuned. Is this correct?
Another, I've heard about this chassis dyno but haven't seen one in person nor I know how it works. How does a chassis dyno works?
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      11-29-2013, 10:55 AM   #20
DVC
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Quote:
Originally Posted by Racer20 View Post
Here's the next chapter:

First, some background

Stiffer and softer aren't really that meaningful when you're talking about a whole suspension system. The reason stiffer is better is that a pair of tires (left and right or front and rear) works better when the weight on them is equal. When you transfer weight between the two, as in body roll, brake dive, or squat, you ALWAYS sacrifice grip.

All else equal, a stiffer suspension resists weight transfer better than a softer one, and less weight transfer means high total traction capacity between all 4 tires.

However, "all else equal" is rarely the case. Some factors that might cause stiffer to be slower:
  • Not enough compliance to maintain grip on a bumpy track
  • Poor front to rear balance (poor steering response or feedback, unbalanced roll, excessive under/oversteer)
  • Non linear, jerky suspension motion or jacking
  • Too responsive for the driver skill, not confidence inspiring. Stiffer suspension means there is less body motion to clue the driver in as to what's going on, and also requires faster reaction times and more precise inputs.

How this relates to the E92 M3:


My understanding is that "sport mode" in an E92 M3 is a fixed steady state setting with no adaptive control. I was surprised when I read this, because you give up the main benefit of EDC when you do this, and this will almost NEVER result in an optimum solution. I can see several of the above scenarios being the case if the shocks are being used in this manner.

The competition package supposedly uses adaptive control for sport mode, which, in theory, should be much better, but I haven't really looked into lap times. The E92 is on my shopping list for my next car, and I would not buy one without ZCP because IMO, the base EDC sport mode is useless. (I haven't driven it in sport, but that's my conclusion based on what I know and the reviews I've read).

Further, keep in mind the Nurburgring is a very unique place, and typically requires quite a bit more body control than our tracks here. A car that is optimized for the 'Ring may be too much for your average driver on an average track here. Plus, tuning on the ring isn't really about lap times, it's about making sure the car handles the various individual corners, bumps, and pavement transitions well.
Thanks for more great info, Racer20 - a great technical explanation of what many of us instinctively believe to be the case.

On the list of factors that could cause a stiffer suspension to be slower, might overly stiff tires (e.g. run flats) contribute to a lack of compliance/ jerky suspension motion? For many enthusiasts, one of the first things we do is ditch the RFTs in favor of some good rubber.
After spending some time in Sport mode in the F30 on both road and track, I haven't experienced conditions where the suspension is lacking in compliance to the point of a reduction in grip compared to Normal mode. (We only get two modes on the F30 - Normal and Sport.)

Once you've had a chance to test an F30 with adaptive dampers (optioned with "DHP", in BMW parlance), I am anxious to hear your thoughts on how well the system performs. Normal mode definitely filters out a lot of the choppy feedback over rougher roads, but there's just too much body pitch/roll for me to enjoy driving in this mode. In Sport, things do tighten up a fair amount to where the ride is much more enjoyable, but there's still a bit more body pitch/roll than I'd prefer.
As a result, like many members here, I have found the car to balance and corner very well in general, but I've been considering options to reduce pitch/roll and improve the car's overall suspension feel (and hopefully the car's ability to grip and turn fast lap time too!) It would be great to read your thoughts on the various considerations that are popular around here... some of those being:
  • Changing Just Springs - Many guys go for just lower springs (e.g. H&R Sport), with a similar spring rate to OEM. I have been considering going with slightly firmer springs, only about 1/2" lower, with matching bump stops. (Dinan plans to release a spring/bump stop kit in January 2014) Seems like these would match up well with the stock adaptive dampers in Sport mode...
  • New Shocks/Springs - e.g. Bilstein B8/H&R Sport springs have been popular and well-regarded
  • Coilovers - KW V3, Bilstein B16, TC Kline, etc. More adjustablity than regular shocks, but maybe not necessary? I've heard that the JRZ kits are in a different league altogether in terms of both comfort and performance...
  • Stiffer Anti-Roll/Sway Bars - I've seen claims that these will address the lateral body roll issue without doing much to change individual shock damping... but I've also heard that too stiff ARBs can be counter-productive.
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      11-29-2013, 11:26 AM   #21
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      12-06-2013, 08:33 PM   #22
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Talking to a colleague, I learned that the E9X M3 uses a Sachs EDC system where the variable valve is actually internal to the piston rod. I'm not very familiar with exactly how it works, but I've heard good things about that system.
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