Smart Air Suspension- Dampening

[bancroftc]

I'm curious about some of the features of the SAS. I've read some conflicting points of view on the forum about the subject of the SAS and their ability to control dampening of the ride, or not. The Tesla website says that the SAS automatically adjusts the stiffness of the ride based on driving conditions. I'm no expert in suspensions, let me say this first. However, I saw it asserted on another thread that the Tesla SAS does not have dampeners and therefore no ability to control the ride stiffness. What is the verdict on this? If it does indeed have the ability to control ride stiffness - and I'll take Tesla at face value here - then why is there no ability to select a ride stiffness manually?

My previous car, a Toyota Sequoia, had an air suspension that could lower and raise in a similar fashion as my Telsa. It also had a selector for "Comfort," "Normal," and "Sport" all of which presented a completely different feel from the ride. Comfort was squishy and soft while sport was firm and let you really feel the road. I'm fairly certain this kind of feature is standard with a lot of sport cars and even SUVs.

Is this type of adjustable ride not available with Tesla? If not, is it by choice or something else that I don't fully understand as a suspension rookie? In summary, if Tesla says the suspension can auto adjust the ride, is it possible that they could add a manually adjustable feature in the future or are there hardware limitations to this?

For the record, I dig my air suspension and use the raise/lower feature daily around town. I love that ability, just curious about it from more of a performance perspective.

 

[JenniferQ]

I was told that there is no performance option. The only performance options are for the steering. We did ask at pickup because our MB GLs all had a suspension option similar to what you describe in your Toyo. It would be nice if it could be added via software in the future. There are a couple of rough spots on the freeway that the SAS feels way too stiff on. It makes us all "grunt" when we hit that spot each time and it's always at 55-65mph because it's on a freeway entrance so there's no way to avoid it.

 

[jerry33]

There was supposed to be a difference between the S and the P, but I don't know if that is still the case or just in the earlier cars. However, there is no adjustment for performance other than the height setting.

 

[lolachampcar]

Two issues-

First
There is no electronic/manual damping adjustability. The dampers are sealed and valving can not be changed. That equates to no changes in stiffness by buttons on the display. The ride may change a very small bit when the ride height is changed but I have never felt it.

Second
The P85D was initially shipped with sport suspension which included stiffer valved dampers. Somewhere around March, Tesla began shipping P85D/P90Ds with standard valved dampers. There have been posts since indicating the sport dampers are back. Perhaps there was a shortage of sport suspension and Tesla exercised its right to change specification without notice. I do not know as I've not kept up with it all (my P85D was a January delivery). Anyone concerned about the type of suspension being delivered on the Ps should search for the thread as there are specific damper part numbers that you can check to identify what suspension is on a particular car.

Hope the above helps.

 

[bancroftc]

Two issues-

First
There is no electronic/manual damping adjustability. The dampers are sealed and valving can not be changed. That equates to no changes in stiffness by buttons on the display. The ride may change a very small bit when the ride height is changed but I have never felt it.


Hope the above helps.

Thanks for the feedback! Question though, if Tesla is saying that the ride auto-adjusts stiffness then how is this not possible? Or am I misunderstanding how a suspension damper works? Thoughts?

 

[lolachampcar]

I've never felt it but best to pass along the word from the team that developed it. It seems like Huibert was focused on spring rate where my interest were more in damper valving -

"
Bill,

Thanks for bringing this up but this statement is actually correct. Air springs by
their nature automatically adjust stiffness in response to load. This means that the
ride frequency remains constant even with large loading changes. This is why you now
often see air springs on the back axles of heavy trucks. The reason for this is that
in order to maintain ride height, the spring must adjust the air pressure inside the
spring. This change in pressure also gives a change in spring rate. Since the ride
frequency is governed by:

2*pi()*sqrt(K/M)

Where K = spring rate and M = sprung mass,

If you change K and M in equal measure, the frequency stays the same. This is one of
the cool things about air springs.

The spring will also change stiffness slightly with ride height since the spring is
now riding on a different portion of the piston which will almost certainly
correspond to a different stiffness since it is almost impossible to make an air
spring truly linear.

Please feel free to pass this along to the other forum participants.

Kind Regards,
Huibert Mees I Director Chassis and BIW Engineering I TESLA MOTORS I 45500 Fremont
Blvd. Fremont, CA 94538
"

 

[CHG-ON]

I haven't noticed a difference in damping between standard and low height. But I can say that the corners with pretty much no roll, which leads me to believe that it must be adjusting to some degree on the loaded side in a curve to maintain a pretty flat plane. I love the SAS.

 

[Niclas]

I recently test drove a P90DL, and it certainly did NOT have the stiffer dampers. It felt much softer than my P85+. The steering feel was also considerably worse in the P90DL, probably due to a combination of the AWD and the softer suspension. Both were on 21" PS2.
I also do not feel any difference in stiffness in the different height settings.

 

[jerry33]

I also do not feel any difference in stiffness in the different height settings.

The difference would be the centre of gravity change, not the stiffness.

 

[Niclas]

Yes there is a noticeable difference in handling when lowered, especially if lowered to the old low setting by using lowering links.
The stiffness, however, is unchanged

- - - Updated - - -

I haven't noticed a difference in damping between standard and low height. But I can say that the corners with pretty much no roll, which leads me to believe that it must be adjusting to some degree on the loaded side in a curve to maintain a pretty flat plane. I love the SAS.

I think you can attribute the no-roll in corners due to sway bars

 

[lolachampcar]

Niclas,
I was very concerned over damper valving when considering going from my P+ to a PD which is why there was so much dialog with Tesla. The original sport suspension on my PD is superb IMO with my reference point being the old 8 cylinder M5s (my previously preferred four door daily driver). If you are considering a PD, you may want to investigate exactly where Tesla is on their current production PD dampers. If you are happy with your P+ (as I was after putting it on coils), you will likely appreciate the performance suspension on the PD. It was a significant improvement for me.

Regarding air and ride height, the info from Tesla indicates that spring rate does change with ride height changes but I could never feel the difference.

 

[Niclas]

Lola,
Yes I would probably have liked the sport suspension on the initial PDs. It it, however discontinued, and there are no indications known to me, that the stiffer suspension is going to be reintroduced. There is also the disconcerting probability that you are never sure what you are going to get when you order a Tesla now. I suppose there were a few PD orders (prior to april) that included the stiffer suspension, but the cars were delivered with the softer suspension. I do not want to end up in a situation like that.
The safest thing would be to buy a pre-owned P85D pre-april build. But how do I get my hands on a P90DL with sport suspension? Impossible I would say atm.
That said, I am very pleased with my P85+, not only the suspension os great, but the steering feel is superior to PDs (AWD sucks in that regard).

 

[lolachampcar]

Wow, that stinks! I've considered moving to a P90DL (if the 10.9 ever comes to fruition) but that would require either (1) ordering early P85D suspension at $2500 per corner or (2) swapping out my P85D units to the new P90DL. Either approach would create Service Center issues should I ever have a damper failure.

Bummer.

 

[Niclas]

Maybe you could get the coil suspension, and have it lowered...

 

[lolachampcar]

I did that on my P+, kinda. I put the coil and P+ dampers on a shock dyno to chariterize the valving. There was little difference in the rears but the front dampers were very different. I ended up buying four corners of coil assemblies from Tesla then using the perch/spring combos off the coil units to replace the air springs on my P+. The result was nice but my PD with air springs is even better.

The key is damper valving and not so much springing. If you can not buy the desired dampers on the car as delivered it makes things harder. There is a guy selling early generation PD dampers over in Europe as he thought they were too stiff

 

[bancroftc]

I've never felt it but best to pass along the word from the team that developed it. It seems like Huibert was focused on spring rate where my interest were more in damper valving -

"
Bill,

Thanks for bringing this up but this statement is actually correct. Air springs by
their nature automatically adjust stiffness in response to load. This means that the
ride frequency remains constant even with large loading changes. This is why you now
often see air springs on the back axles of heavy trucks. The reason for this is that
in order to maintain ride height, the spring must adjust the air pressure inside the
spring. This change in pressure also gives a change in spring rate. Since the ride
frequency is governed by:

2*pi()*sqrt(K/M)

Where K = spring rate and M = sprung mass,

If you change K and M in equal measure, the frequency stays the same. This is one of
the cool things about air springs.

The spring will also change stiffness slightly with ride height since the spring is
now riding on a different portion of the piston which will almost certainly
correspond to a different stiffness since it is almost impossible to make an air
spring truly linear.

Please feel free to pass this along to the other forum participants.

Kind Regards,
Huibert Mees I Director Chassis and BIW Engineering I TESLA MOTORS I 45500 Fremont
Blvd. Fremont, CA 94538
"

This is great info, thanks for sharing. I guess that pretty much answers my question. So the Tesla changing stiffness automatically is more a product of the vehicle responding to loading to maintain a consistent ride height on all four corners. Based on that, is it safe to assume that the suspension responds dynamically to a hard cornering maneuver? On a sweeping right turn would it increase pressure/stiffness on the front left and reduce on the back right to balance out the transfer of weight? Or something like that..?

- - - Updated - - -

I haven't noticed a difference in damping between standard and low height. But I can say that the corners with pretty much no roll, which leads me to believe that it must be adjusting to some degree on the loaded side in a curve to maintain a pretty flat plane. I love the SAS.

I thought I had noticed the same. Sounds like it may indeed be the case based on Lola's comments.

 

[lolachampcar]

The info from Tesla says the air spring's spring rate changes based on loading position. If that is the case, and I have never felt it so I can not confirm it, then there should be a change in rate between the loaded and unloaded springs in a corner. I've never felt it so the effect, IMO, is small.

There is no active management of air springs on a short time constant. All the control is on a longer time constant to manage ride height. Nothing happens when you are cornering (likely steering angle inhibits the air pump).

Links to suspension module control and Model S damper dyno plots of needed.

 

[3mp_kwh]

A dynamic suspension, changing to cornering conditions as it levels mid-sweeper, is the stretch I think Tesla drives at when suggesting it is like other optioned suspensions. But its not optioned, and as mentioned it is the damper valving, bump and rebound, most people tweak. Moton, Bilstein, KYB and Koni all offer valving adjustability, sometimes from the cockpit, sometimes at the shock tower. These are not variations of spring rate, but are common ways to offer adjustability.

I gained access to the parts list, as a MA resident, and can say there was no entry for P90D(L) 'performance susp' as of a month ago. Someone is selling an early P85D air spring set, in the parts section and he's not the only person to prefer the later/current spring/damping setup (also Sorka). I go back to the fact this car has so little roll that I think people get a little too worked up about the use of the same parts across the MS. There isn't much roll to tame in these cars, and I cut Tesla slack. In support of coils, I'd rather a car roll to its limit, and stay there, than get that feeling my spring rate is changing in the middle of a high speed turn. My belief is that, at fast speeds, most people feel more confident at how "flat" the SAS car feels, but when faster, near where the car is going to begin slipping, those same mid-turn SAS adjustments become another feedback to decipher, and are actually less confidence inspiring.

When a car slides, it isn't "hooked up", and the loaded side lifts. I haven't driven SAS enough to feel like I'm not losing grip as the loaded side gets pumped up. That "dynamic" change isn't one that "sold me" on the feature. The marginally nicer ride? That's different.

 

[lolachampcar]

I do not believe the suspension can react sufficiently fast enough to be active while cornering. I believe these transients are filtered out by time or simply ignored as a function of steered angle.

Having the battery below the wheel center line significantly lowers Model S' roll center and thus Tesla used the larger roll bar on the front of the car to improve turn in feel at the expense of head snatch.

 

[Cyclone]

My 2013 S with air definitely stiffens up as I raise the suspension. I had my service center look at it because I was "bottoming out" the suspension without hitting the ground over speed bumps at work. Service Center figured out t was because I was on Very High. Switched to High for those bumps and no problem anymore. They told me that at Very High, the car stiffens up analogous to Dr. Frankenstein's monster and gets much more rough.

However, the ability to dynamically stiffen or adjust the dampers on the car doesn't exist. The only control point (that I am aware of) stock is the height.