Suspension - adjustable height or adjustable stiffness?

Would you choose SAS or SAD or keep the money?

  • Adjustable height $2000

  • Adjustable stiffness $1000

  • Neither $0

  • Neither, with Comfort/soft dampers $0


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4701

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#1
Imagine you are going for your Model 3 customisation. You can choose either you want Smart Air Suspension (SAS), which will allow you to raise the vehicle an inch while driving slowly with location memory - though will always leave you in one specific "sporty" setting with current dampers (keep in mind only Normal or Low can be used for longer driving, and difference between lowest and highest will be up to 2"). This is the same option offered on Model S.
Imagine this is a stand-alone option not bundled with anything else. Costing roughly $2000.

Or you would rather choose dampers, that can change their stiffness according to slider on the screen (next to steering effort slider). Of course, in case of Tesla, we would have Smart Adjustable Dampers (SAD). That means that car will remember your preference according to location and/or speed (if you ask it to remember). So in case of that hellroad on your commute, it can automatically switch to Comfort mode. And when you get on that new highway, it switches back to Sport mode (identical to fixed dampers offered with standard suspension and same damping settings as on SAS). In case you drive in Sport mode all the time, it can (later, with software update) remember speedbump GPS location and switch to soft mode for a second when you pass them.
This will cost you roughly $1000 (took it from BMW option list).

Same thing on BMW
Forget sensors, there aren't any, it's very simple system with one wirepair to each damper, either ON or OFF.

You can either choose SAS, SAD, or neither. Both can't be equipped simultaneously. In case you choose neither, you get fixed sporty suspension that is offered right now. Both options can be chosen with 18" and 19" wheels.

EDIT: Added option to prefer Comfort dampers (same setting as with adjustable dampers in Comfort mode). This is medium stiffness (like BMW 3-series without M-sport suspension). Comfortable, not mushy. It's free, but you can not change it in the menu.
 
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JWardell

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#2
The answer depends on the coiled alternatives. I will pay extra for a coiled sport suspension. If that's not available or the standard coiled suspension is not fun enough, then I might pay for adjustable suspension, if I find solid evidence that it is actually an improvement. Of course, price is also a factor. BMW has been decent with these offerings IMO
 
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4701

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#3
There are two ideal suspension settings: best handling/safety and best comfort (least bouncing).
It looks like this:

In case of SAS and current dampers, owner will always drive with S-settings, with best safety and not best comfort.
In case of comfort dampers, owner will always drive with C-settings, with pleasurable oscillations
(as much as is possible with low to the ground vehicle).
In case of SAD, owner can choose either C or S on the move (but not anything in between, those systems that can smoothly adjust dampers cost more). It's also possible to program vehicle to switch to Sport mode whenever there is wheelslip or vehicle accelerates/brakes hard. Switchover happens with milliseconds.

The answer depends on the coiled alternatives. I will pay extra for a coiled sport suspension.
Current Model 3 dampers appear to be very close to S-line (possibly initial dampers were slightly to the right of S, and updated ones slightly to the left; though one forum user commented, that handling got better after upgrade/recall, therefore it is possible, that older Model 3 dampers were too far to the right). Keep in mind, making them any stiffer than S-settings will reduce traction, safety and comfort simultaneously. Even though owners might do that, manufacturer should always fit their suspension in between S and C lines. You can't pay extra, as coiled sport is standard on Model 3 right now:)

Adjustable dampers do not cost a fortune because technically, vehicle part count doesn't change a lot. Regular dampers are changed to dampers that have a 12V valve inside. For manufacturer, this means 1 part for 1 part. And 4 wire pairs added to main wiring harness. And now, either have them all work simultaneously with a single 12V relay or adjust them according to scenarios with single cheap module (less than $50).

PS: Air suspension could bring green line ever so slightly higher (half an inch). So with fixed "Sport" dampers, comfort level should improve by 10-20% (compared to "C" dampers without SAS). It's true that "Comfort" dampers with air suspension will be ideal in terms of comfort (this is why SAD and air suspension is standard on BMW 7-series flagship).
 
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PNWmisty

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#4
Suspension tuning is more art than science. Race cars change springs/dampers for different tracks. Adjustable dampers don't really solve a lot because there is some interplay between the springs and dampers. For a given spring rate and amount of suspension travel, there isn't a lot of room to play with different damping rates - all those factors play together. The real issue is that a system that automatically softened the dampening based on location could cause more harm than good. There are speed bumps/potholes out there that will damage wheels and/or suspension components if the damping was too low. High damping rates are good for preventing damage on big hits. Softening the damping rate right before a big hit could be exactly the wrong thing to do. Also, if the compression damping was softened without simultaneously adjusting the rebound damping, the suspension could "pack down" over rough roads. This makes the ride even more uncomfortable. It's counter-intuitive, often higher damping rates lead to a smoother ride over irregular roads.

In my experience, a suspension well tuned for sporty driving on public roads is different from a suspension well tuned for driving on the track because you shouldn't be driving 10/10 on public roads. And the good suspension well tuned for public roads is also about the most comfortable for someone like me who doesn't like the sea-sick feeling from overly soft suspensions. While it's true that some people like a very soft ride, often termed "luxury", I don't find that luxurious at all so I have no interest. Just give me a well tuned suspension for sporty driving and I'm happy. Contrary to common perception, a suspension that provides peak performance on the variety of situations found on public roads is not all that stiff, a supple suspension grips better when the road is not perfect.

The big trade-off between comfort and performance doesn't have to do with damping rates at all, rather it's anti-sway bars. A very effective anti-sway system will increase performance substantially while simultaneously making the ride too harsh for some people. If you are in search of more "sport" at times without ruining the ride, you might look at anti-sway bars with electro-mechanical lockouts. But I'm more than happy with a quality, well tuned, non-adjustable suspension for it's simplicity and cost effectiveness. As long as it's well tuned to be competent in a variety of situations. Comfort for me has more to do with whether the seats are supportive in the right places than anything to do with adjustable damping rates.
 
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4701

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#5
I agree. If tire fully bottoms into a pothole, while vehicle just bottomed due to previous jump, the damage is done more easily.
But we are not talking about mushy suspension option at all. And there are no excuses to force buyers use hard dampers.

I've never felt overly soft suspension on any European vehicle. My friend once got old GMC truck, that was bouncy as hell:tonguewink:
There is a reason why Model S took over suspension principles from Mercedes and why Model S feels good on road.
We can be sure, a lot of work has been done (decades) for BMW, Merc suspension setting tuning. It's not going to happen
overnight even with a thousand engineers.

Adjustable dampers are one of the most appreciated options on BMW 5-series bytheway. Most car reviewers specifically mention that.

PS: for educational purposes: why softer springs give more safety and stability on the road (and not visa-versa):
 

PNWmisty

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#7
PS: for educational purposes: why softer springs give more safety and stability on the road (and not visa-versa):
I've seen that guy address a number of other unrelated subjects on his u-tube vids. He's pretty good, this video included (although it was a very abbreviated intro to the subject of spring rate and he glossed over a lot of pertinent facts).

Near the end of the video he did imply that a race car would use softer springs for a track that had a bumpier surface. And he's correct about that. Of course the change requires a number of other simultaneous changes which are completely impractical on a road car.

I'm heartened that some early Model 3 owners are reporting the ride is not as compliant as they were expecting. That's because US drivers have a general market preference for overly soft suspensions and therefore the market meets those preferences. In Europe and Japan, suspensions tend to be more firm. A softer suspension uses up it's available travel more quickly than a firmer suspension and therefore has less capability to drive on rougher roads at higher speeds (without bottoming) vs. a car with a more stiff suspension.

Of course all of this is gross generalizations because of the way damping plays into it. Damping is very complex. A good vehicle damper will have various damping rates depending upon how fast the suspension arm is trying to move. In general, the faster the suspension arm is trying to move, the less firm the damping becomes. This allows the vehicle to feel solid (not floating) on a relatively smooth road with gentle undulations while still allowing the suspension to soak up more sudden bumps.

I imagine a vehicle with adjustable damping that is limited to two modes (either firmer or softer) would either adjust only the low speed damping (refers to speed of suspension movement, not vehicle speed) or it might adjust both damping circuits simultaneously (probably the former). Either method would have drawbacks, especially considering there is no way to adjust spring rate. It is possible to have electro-mechanical spring pre-load adjustment but all this does is adjust the height at which the vehicle rides on it's springs, commonly called the "sag" and the primary reason to adjust this is to deal with different amounts of cargo/passengers. The spring rate remains unchanged. To adjust the spring rate is more complicated. It can be done by replacing the steel with air. But air suspensions lose one of the best features of steel springs, the fact that steel springs have a constant rate (which is desirable). Dual rate springs are a gimmick that never seem to work well in the physical world. For a coil spring to function as a dual rate, the softer coils must become physically bound to each other during compression. Otherwise the higher rate portion of the spring is not doing any of the work.

Just give me a nice firm suspension so I don't feel like the car is a boat, make sure the spring rates and damping are well matched and include effective anti-sway bars and I'm a happy camper. Cadillac "cush" is sickening to me.
 

Prodigal Son

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#8
I've owned two cars with fancy suspensions. Between the two of them I spent a hair over $10,000 in suspension repairs out of warranty.

Done with that crap, normal struts and springs for any car I expect to own longer than the bumper to bumper warranty lasts.

I, for the record, think the Model 3 ride quality is fine.
 
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4

4701

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#9
Done with that crap, coils and springs for any car I expect to own longer than the bumper to bumper warranty lasts.
Did you mean "springs and shocks"? If yes, then well, for Model 3, I agree. But adjustable shocks are as reliable as fixed shocks. I've never heard of failed 12V magnetic valve. Anywhere, not only in shocks. But there is nothing else inside. Just a regular shock with two oil-passages, one of them is blocked on demand. Though shock does cost slightly more, it's around 1000€ to replace all of them. Regular shocks around 600€. Dampers should last at least 150-250Mm (100-150k miles).
 

PNWmisty

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#10
Though shock does cost slightly more, it's around 1000€ to replace all of them. Regular shocks around 600€. Dampers should last at least 150-250Mm (100-150k miles).
The best dampers could only last that long if rarely driven at higher speeds. For a car driven on the freeway at 70 mph, even a quality damper would likely lose 20% of their damping before hitting 50,000 miles, Sooner if the speeds were higher, the roads rougher and the temperatures warmer.

I would rather have dampers that were replaced on a schedule or when they had lost that first 20% of their damping than adjustable dual rate dampers that, due to cost, were left in place until they had lost 50% of their damping. The model 3 is a heavy car. The amount of compression damping needed is directly proportional to the sprung weight of the vehicle. And the amount of rebound damping needed is directly proportional to the weight of the unsprung wheels and suspension components (or more accurately, the moment of inertia of those components). Heavier cars need more damping and the energy of damping is wasted as heat. That's why dampers get warm after freeway driving. And the source of the energy creating the heat in any car is the drive motor.
 
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4701

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#11
My BMW has driven more than 200 000 miles and rear dampers are at 49% 50%, still from factory. Front dampers have been replaced few years ago (like 150 000 miles). New dampers give around 70-80% result on the machine. Those new ones at the front still give full 80%.
Technician said that because I have air suspension in the back, rear dampers would give 60-70% when new as a measurement result, though they are absolutely new.
Dampers last longer than what you said. And this vehicle often got 100-120mph when it was cruising on german roads years ago.

They are counted as worn when results dip below 40%. So from 80% down to 40%.
AFAIK, in US, people rarely drive vehicle more than 20 000 miles per year.
That is a lot of years before replacement is needed.
 

PNWmisty

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#12
Hopefully the Tesla dampers are as good as your BMW dampers have been. The German Autobahn is maintained and kept in MUCH better condition than US Interstates! And BMW must use the best dampers in the business because most cars are sacked out much sooner. It's just that most drivers cant tell the difference until they below 50%.
 

Prodigal Son

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#13
Did you mean "springs and shocks"? If yes, then well, for Model 3, I agree.
Er, yes. nice catch. I blame… *spins wheel of blame* the cat!

But adjustable shocks are as reliable as fixed shocks. I've never heard of failed 12V magnetic valve. Anywhere, not only in shocks. But there is nothing else inside. Just a regular shock with two oil-passages, one of them is blocked on demand. Though shock does cost slightly more, it's around 1000€ to replace all of them. Regular shocks around 600€. Dampers should last at least 150-250Mm (100-150k miles).
Yeah they could be fine, I'm just very wary of any suspension that adjusts from anything besides a wrench or a knob at this point.
 
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4701

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#14
So it appears we can sum up some results.
If anything, potential owners would rather pay $1000 to change stiffness between firm sporty and smooth comfort.
Some consider saving money and choose non-adjustable firm dampers.
And almost nobody was interested in raising vehicle an inch nor having smooth comfort dampers only.

I personally would go with adjustable dampers as well. If that was not available, I'd choose comfort fixed dampers.
I will never choose air suspension nor would I keep firm dampers. If that means throwing out OEM ones, so be it.