The WHY? of it BMW - Air Suspension

[Human]

I'm very far from an engineer, so it's only an opinion, but all air suspensions I drove/could ride with were very comfortable, BUT did not give the same road-feel as a steel one. The car is somehow "floating", even the hard suspensions of a Cayenne with pneumatic dampers doesn't allow the same contact as with conventional springs.

This must be particularly true on front suspensions, where BMW chose to use steel dampers, surely not to compromize the road and steering feel of the car.

Whereas the rear axle has less influence on these factors, and it is very obviously the rear axle who takes the more benefits from these air suspensions due to the weight changes (number of passengers, luggages) and has the most influence on the comfort of the passengers, especially at the rear.

So, steel springs at the front for road feel, air springs at the back for comfort and charge adaptability. As far as ride height is concerned... Well this is useless to say the least unless you live in Amazonia.

Of course, with this, you can't achieve the comfort of the S-Class and its all-air adaptive suspensions, but it is not what BMW wanted to do and if you're that concerned with comfort, then you might want to switch to Benz .

For the X5-X6 I don't know, they really could benefit from air suspensions as it allows a more supple ride while limiting bodyroll. And the air-suspended Cayenne is no comfort-oriented SUV either... You will notice however that the "sportier" GTS does come with steel springs.

Thank you for the info!
Switch to Merck.....mmmmm.....NOPE! I respect the Swabian Manufacturer ALOT! BUT: Owned 2x new W203 C-class cars, test drive a E46 325i back in 2003....I am the proud owner of my 4th BMW know
I am not the one looking for the comfort, it is the motoring press - their opinion about the F01.

 

[EnI]

F01 comfort ... The British journalists complained quite a lot ... They always do when the BMW's comfort is in question.

They go & ride the cars on their s..y roads, and of course no car is even close in comfort to MB (or perhaps Lexus).

And that's not enough for them ... they decided that segment (of 7er) is all about ultra-comfort, and super-silence, and easy-to-drive - no other alternative is possible. And therefore, of course, the 7er is not good enough for that segment.

Yet as I said: BMW offers sporty dynamics over comfort, and people buy it for that reason. Otherwise they go to MB or Lexus or etc.

Mind that usually customers & journalists don't have same taste / expectations / needs & demands etc.

 

[martinbo]

It has nothing to do with Brits and their "sh..ty" roads. You don't get the same complaint from them regarding the S-Class.

BMW could easily make the 7er ride as plushly as an S-Class. But they don't because it's not in their intent or direction. BMW doesn't want a facsimile of an S-Class. They want a car with its own identity and character that remains within the ethos of the brand. Hence the 7er - why? - because it's an alternative offering to the S-Class. Not a mere "me too" copy. I mean, if I was in the market for an S-Class why on Earth would I want a copy of one for the same money? Now, if I was in the market for a sportier S-Class type vehicle - well, clearly I'd be looking for a 7er.

 

[EnI]

^

What else have I said?

 

[Human]

F01 comfort ... The British journalists complained quite a lot ... They always do when the BMW's comfort is in question.

They go & ride the cars on their s..y roads, and of course no car is even close in comfort to MB (or perhaps Lexus).

And that's not enough for them ... they decided that segment (of 7er) is all about ultra-comfort, and super-silence, and easy-to-drive - no other alternative is possible. And therefore, of course, the 7er is not good enough for that segment.

Yet as I said: BMW offers sporty dynamics over comfort, and people buy it for that reason. Otherwise they go to MB or Lexus or etc.

Mind that usually customers & journalists don't have same taste / expectations / needs & demands etc.

That is just and true! I owned a C180 K 2002 model. Ride was very comfortable. Our local BMW dealer had a 325i with 16k, full house sat nav, sun roof, auto, Xenon etc.....
I drove it....fell in love with the cars dynamics and handeling. The firm ride + E46 excellent build quality (E46 had MUCH BETTER BUILD than W203) won me over, as I said...I never looked back again. Now I own a white X6 35d Best thing that BMW could have done for Naas Human, I love coupe's, yet also the X5...I had a 2004 4.4i....YIHAAA! BMW combined the two 650i+X5....And made me the happiest man alive!!!!!

 

[EnI]

^Gret.

So, please tell some of our members (and the journalists) the X6 makes sense for some ... And it's not that pointless at all.

 

[Human]

BMW 7er vs. Panamera Suspension???

On the same topic again!

Our whole discussion regarding Air suspension - the why & why not - has been trown out the window by PORCHE AG.

Seems that perfect control and handeling can be achieved by, 4 wheel Air suspension. On the Panamera they use the double wishbone suspension just like BMW on the new 7er. With one major difference AIR in the place of conventional steel springs....Seems to me my favourite brand (BMW) is not into that much suspension technology.....especially compared with rivals Daimler AG & Porche AG.....

 

[martinbo]

martinbo bites his tongue until it bleeds...

 

[Monster]

I am not suspension expert but it doesn't matter which technology a car manufacturer adopts as long as they can achieve the desired end result, it is all good.

 

[Merc1]

Thats true, but it is an interesting question.

My guess here would be the Porsche wants the S/CLS/XJ crowd to want this car also and for them not to find it too rough riding like a 911 can be when you step out of a big luxury car.

Now Porsche is still an engineering driven company on so many levels so they may have achieved something remarkable here if this car outhandles the competition while delievering a luxury car ride...the holy grail of suspension engineering/tuning.


M

 

[Sunny]

I know X5/6 M has air suspension in the rear. But they chose not to use it in the front, so there must be a reason.

 

[Sayyaaf]

We got the answer before by the expert Martin and I think that's what he meant by his reply. Please qoute him from the 7 series discussion forum (760li i think). In simple words, the Beemer simply used the coils instead of the air suspension because they believe it has more road feel and feedback than the air suspension. Moreover, steering can be preciser/nimbler with coils. Personally I think both ways can be gotten right with the correct calibration.

Regards

 

[Gullwing]

That system looks just like what is on the S class, the lower end models with air suspension. The better suspension is ABC.

Depending on what you really want ABC, air, or springs will work best. If one was the "best" for everything, that would be all you would find.

 

[bmer]

On the same topic again!

Our whole discussion regarding Air suspension - the why & why not - has been trown out the window by PORCHE AG.

Seems that perfect control and handeling can be achieved by, 4 wheel Air suspension. On the Panamera they use the double wishbone suspension just like BMW on the new 7er. With one major difference AIR in the place of conventional steel springs....Seems to me my favourite brand (BMW) is not into that much suspension technology.....especially compared with rivals Daimler AG & Porche AG.....

Since you are continuing with the same topic, there is no need for another thread. I've merged this new thread with your old one.

Furthermore, it seems the question you are asking has already been answered in the previous posts...

 

[martinbo]

Oh Sayyaaf, I wish I was an expert. But sadly, no - there's no expertise in this area.

However, it doesn't take any rocket science to figure out that, at an elementary level of discussion, conventional steel springs have a narrower operating envelope than air suspensions. Similarly, the more adjustable nature of the air spring means that the suspension characteristics can be more readily altered to suit the driving conditions or mood of the driver.

The tuning of steel-sprung suspensions is a perfect example of achieving the best possible compromise when it comes to rationalising a car product for its intended audience and application.

Suspension tuning however is a special and long-standing art and many manufacturers have honed their skills over many decades to achieve the capability / ride / handling trade-off. In my rudimentary understanding of the issue I surmise the following:
The narrower the operational envelope of vehicle, the more suitable steel springs are for 99% of the application. It's why practically every sports car out there has steel springs. With conventional springs it's all about the "spring rate" of the metal spiral or leaves, in other words, the force with which a spring compresses or uncompresses. The stiffer the spring, the quicker it controls body movement, thus being more suitable for low, sporting cars. Softer springs make for a more comfortable ride but there's little lattitude for suddenly imparting sporty, stiff body control.

Recent advancements in shock absorber (damper) technologies has seen many manufacturers increase the versatility of the suspension within the current operating envelope of the steel springs. A fine example is that of the new magneto-rheological technology (is it from Sachs?) dampers found in the Audi TT. What these clever shocks do is impart a more comfortable ride by enabling the springs to flex more freely in comfort mode (by reducing the amount of internal resistance in the shock) and then to tighten things up, thus allowing the spring to flex less freely. This does not, however, change the operating envelope within which the TT's springs are intended to run: the TT is a road car, designed with specific handling characteristics.

In cars like a Range Rover, air springs make a great deal of sense. Because of the variation in road speed and in terrain, air springs not only can significantly raise or lower the body relative to the road conditions, they can also stiffen or loosen the spring rates - stiffer at higher speed, looser at low speed over bumpy ground for comfort. Here we can see that the operating envelope of the spring is much greater than that of a TT. Porsche do not offer air suspension in any 911 - regardless of its sophistication. And yet, on a Cayenne Turbo or GTS the optional fitment is commonplace - again it's that operating envelope.

Another cool thing about air suspension is that it can, by virtue of electronic sensoring, be rapidly adjusted to cope with road conditions, cornering attitude and driver disposition more readily than fixed rate conventional springs. This is the approach behind Mercedes Benz ABC suspension which is designed to impart terrific levels of comfort whilst maintaining the decorum of body control (read body roll) befitting a prestigious Mercedes.

In the case of the Panamera, Porsche clearly want to offer the car with a broader spread of talent to thus appeal to the discerning buyer who wants both luxury conveyance, with a plush, passenger cosseting ride together with the true sporting demeanour of a proper Porsche for when the occasion calls for it. Again, here's that broader operating envelope.

Of course, a Panamera doesn't need air suspension to be able to tackle the Nurburgring, conventional steel springs will do the trick, though they may not be as comfy in town nor as stiff and controlling on a circuit as air suspension.

Now, another factor influencing the behaviour of a spring and it's ability to suspend (support) the body is load. This is the predominant reason for putting air suspension in the rear axle of the X5 M. This is a levelling function - it ensures that the vehicle stays level and doesn't sag over its rear axle when loaded - thereby maintaining the desired levels of handling needed.

Air suspension and related systems are of course heavy, complex and expensive and are thus routinely avoided in all but the most expensive cars or fit-for-purpose applications.

And, that's why we've not seen air suspensions in the 7er (just yet but who knows!?) It's because BMW have fine tuned the springs and dampers to achieve the desired ride and handling characteristics within that vehicle's operating envelope.

So, Human, I reckon this should go some way toward facilitating discussion for you...

 

[Human]

Thank you! I do see the whole reason for why BMW chooses to use steel.
I just see the Panamera as a new 'leader' when you compare the suspension used by Porche for this car. I have read about it and it seems to be better than ABC!?
AND WONDER WHY A BMW 7 (same price bracket) DOES NOT USE A MORE TECHNICAL AIR SPRUNG SUSPENSION.....Would the steering feel in the Panamera and handeling be inferior to that of the 7? I don't think so! And what really comes to mind is the comparison test between the new 7 er vs. S-class, the bodyroll of the 7er was worrying!

 

[Zafiro]

comes to mind is the comparison test between the new 7 er vs. S-class, the bodyroll of the 7er was worrying!

if you refering to Edmunds Comparison the bimmer wasn't equipped with Active Roll Stabilization & Integral Active Steering. So take the test with a grain of salt.

 

[coolraoul]

I don't think you can say that one car is better than the other only based on the fact that one has air spring on both axles and the other only at the rear.

The Beemer will not be able to be as "versatile" but more a compromise, whereas the Porsche will allow you to choose comfy or sporty. However, it does not mean this compromise is not good.

Instead of active springs, BMW uses active anti-roll bar. It's easier and lighter as a solution. It is effective against bodyroll (I drove an e65 with it, it felt much lighter and smaller), however it's nowhere near as comfortable as an S-Class.

If the aim is not to be super-comfy, then why bother with complex and heavy air springs?

The Porsche on the other hand wants to be comfortable as an S and sporty as a 7er, for that you need air springs.

However, comfort is also influenced by the other suspensions components (fine-tuned with comfort or feeling in mind..), steering ratio... Just fitting soft dampers doesn't necessarily make a car comfortable.

Usually, by hardening the suspensions, you don't radically alter the feeling of the car, you only alter the bodyroll and suspension comfort. The steering feel and directness, the neutrality (or lack of) of the chassis and its way to deal with corners, the noise perception, the basic characteristics of the motor and gearbox (depsite the eventual sport-mode) can't be changed just by softening the dampers.

Even these "sport-buttons" changing dampers, steering weight, motor and gearbox map, don't have such an influence on the chassis that the car goes from truly sporty to truly comfort-oriented. It stays as it is, only bit less or bit more.

The Cayenne in soft mode is still not very comfortable, the S-Class in hard mode is still not really sporty (even without bodyroll it doesn't give much road-feel, that is part of the comfort-fine tuning)...

Also, first reviews, with no competitor's car and on a Porsche test track, driven by Porsche testdrivers, is not really revealing what the Panamera really feels like. For that we need to wait for proper reviews.

 

[Centurion]

Thanks for the lesson Martin. Some newsworthy information you addressed in that post.

 

[EnI]

if you refering to Edmunds Comparison the bimmer wasn't equipped with Active Roll Stabilization & Integral Active Steering. So take the test with a grain of salt.

Yes, that 750Li wasn't equipped with Active Roll Stabilization (= Dynamic Drive), nor with 4-wheel steering (= IAS) - both part of Sports Package in US market.

While S-class used in the tested featured Active Body Control system.

As said: Active Roll Stabilization is essential in long or / and high cars.

Some of those cars use "air springs" for active roll stabilization (eg. MB with ABC etc), while BMW use different anti-body-roll solution (Dynamic Drive = hydraulic anti-roll bars on both axes).

Btw, just like X5, X6, & 5er Touring also the 7er can be equipped with self-leveling rear air suspension (preventing rear-suspension overload when car fully laoded).


****

I guess BMW can achieve best result of handling vs comfort combination with the steel springs (or only rear air suspension) while roll stabilization is achieved with other tech (Dynamic Drive system).

Also the 4-wheel steering has also proved to be an advantage on large (long) cars ... Providing better handling (slalom).