[TurtleBoy]

Originally Posted by matowi

So, to stir up the topic even more, and to add value to the entertainment aspect of this thread, let me share an observation that my M60i X5 on the adaptive M Performance Professional suspension with 22 inch non-RFT wheels rides better than a 2021 7-series I just sold, which had executive drive system (air suspension on all 4 corners with active anti roll bars) and rode on 21 inch RFT wheels

Now, for full disclosure, the precise measurement instrument I applied to arrive at the conclusion mentioned above is my very own bottom. It’s an entire science department that deals with the question of “what it means that a car drives better”. But that question wasn’t asked by OP, so I’ll stay mute on it for the moment

In order to accept those results, we need to know when the last time was your butt was calibrated.

[MotoWPK]

Originally Posted by BlkGS

Understandings of physics doesn't appear to be a prerequisite for this conversation, so don't let that deter you.

To summarize the physics involved...

The pressure/volume relationship of a gas in an adiabatic process is:

P2/P1 = (V1/V2)^n

where P1 and V1 is the pressure and volume of the gas in the air spring at the static ride height, P2 and V2 the pressure and volume of the air spring deflected. n is the adiabatic gas constant which for air is 1.4.

Adiabatic is applicable here because the duration of the process, suspension deflection, is short enough to provide for minimal heat transfer of the gas to its surroundings.

Using this relationship with dimensions found for the X5's suspension and gas struts, the pressure ratio from the static condition at the normal ride height for various suspension deflections in compression is:

Compression
Deflection - mm Pressure deflected/pressure static
10.....................................1.08
20.....................................1.16
30.....................................1.26

The same calculation starting from the sport level ride height, 20 mm lower than the normal level ride height, is:

Compression
Deflection - mm Pressure deflected/pressure static
10.....................................1.26
20.....................................1.37
30.....................................1.50

Two things to observe here;
1) The greater pressure rise for the same suspension compression, therefore, a high spring rate, and,
2) The pressure ratio increases with the degree of compression resulting in a corresponding increasing force, or a variable spring rate.

To further clarify this last point, an increasing force with increasing deflection is not spring rate, spring rate being define as the change in force per unit deflection. So for the above examples, a deflection from 20mm to 30mm produces a greater pressure (force) increase than the change in deflection from 10mm to 20mm - a variable spring rate.

By comparison, the common coil spring of constant wire diameter, coil diameter and coil angle and pitch produces a force proportional to deflection; i.e. compress the spring 10% and the force increases 10%, compress the spring 20% and the force increases 20%, that is, a constant change in force per unit deflection - a constant spring rate.

[Di3s3l_Power]

Originally Posted by MotoWPK

To summarize the physics involved...

The pressure/volume relationship of a gas in an adiabatic process is:

P2/P1 = (V1/V2)^n

where P1 and V1 is the pressure and volume of the gas in the air spring at the static ride height, P2 and V2 the pressure and volume of the air spring deflected. n is the adiabatic gas constant which for air is 1.4.

Adiabatic is applicable here because the duration of the process, suspension deflection, is short enough to provide for minimal heat transfer of the gas to its surroundings.

Using this relationship with dimensions found for the X5's suspension and gas struts, the pressure ratio from the static condition at the normal ride height for various suspension deflections in compression is:

Compression
Deflection - mm Pressure deflected/pressure static
10.....................................1.08
20.....................................1.16
30.....................................1.26

The same calculation starting from the sport level ride height, 20 mm lower than the normal level ride height, is:

Compression
Deflection - mm Pressure deflected/pressure static
10.....................................1.26
20.....................................1.37
30.....................................1.50

Two things to observe here;
1) The greater pressure rise for the same suspension compression, therefore, a high spring rate, and,
2) The pressure ratio increases with the degree of compression resulting in a corresponding increasing force, or a variable spring rate.

To further clarify this last point, an increasing force with increasing deflection is not spring rate, spring rate being define as the change in force per unit deflection. So for the above examples, a deflection from 20mm to 30mm produces a greater pressure (force) increase than the change in deflection from 10mm to 20mm - a variable spring rate.

By comparison, the common coil spring of constant wire diameter, coil diameter and coil angle and pitch produces a force proportional to deflection; i.e. compress the spring 10% and the force increases 10%, compress the spring 20% and the force increases 20%, that is, a constant change in force per unit deflection - a constant spring rate.

^excellent

Selecting "Sport" suspension on my 45e makes a big difference. I wouldn't want more stiff. It think is just right in terms of stiffness and harshness

[tkim91321]

I have the m60i with air suspensions, paired with 20” wheels for max comfort.

No regets whatsoever.

[nZtiZia]

Originally Posted by BlkGS

That's why I keep trying to make you realize that you're misunderstanding what progressive springs mean. Progressive means "as you push further, it pushes back harder". It does not mean that the spring rate rates stiffer as the bags have less air in them.

Think of filling up a tire. At 10 psi you can use a little bicycle pump to the fill the time easily. At 20 Psi it's a bit harder. At 30 psi it's noticably harder. At 40, you're struggling. At 50, forget about it. That's what progressive rate means, the more the spring compresses from nominal, the more spring rate it exerts. It's why if you pull back on an archery bow more, it shoot the arrow further, because you're storing more energy in the spring.

Steel springs can be progressive rate too, and most are. They do this by adjusting spring dimensions and spacing.

But hey, we can agree to disagree. Sometimes you can't explain technical things to people when all they can understand is "it costs more so it must be more good".

this is the root of your misunderstanding: you can’t use tires or air mattresses as analogies to what’s happening in air suspension because they’re not simply air bags!

now read MotoWPK post above about the physics involved, though I don’t expect you to understand it one bit. you’ve yet to prove your “understanding” with anything but non-applicable articles and “it just doesn’t work that way.”

may the good lord help you

[JoeAyalaM]

Originally Posted by MotoWPK

To summarize the physics involved...

The pressure/volume relationship of a gas in an adiabatic process is:

P2/P1 = (V1/V2)^n

where P1 and V1 is the pressure and volume of the gas in the air spring at the static ride height, P2 and V2 the pressure and volume of the air spring deflected. n is the adiabatic gas constant which for air is 1.4.

Adiabatic is applicable here because the duration of the process, suspension deflection, is short enough to provide for minimal heat transfer of the gas to its surroundings.

Using this relationship with dimensions found for the X5's suspension and gas struts, the pressure ratio from the static condition at the normal ride height for various suspension deflections in compression is:

Compression
Deflection - mm Pressure deflected/pressure static
10.....................................1.08
20.....................................1.16
30.....................................1.26

The same calculation starting from the sport level ride height, 20 mm lower than the normal level ride height, is:

Compression
Deflection - mm Pressure deflected/pressure static
10.....................................1.26
20.....................................1.37
30.....................................1.50

Two things to observe here;
1) The greater pressure rise for the same suspension compression, therefore, a high spring rate, and,
2) The pressure ratio increases with the degree of compression resulting in a corresponding increasing force, or a variable [...]

Exactly.

Thanks for doing the calculations.

Let's hope some persons can understand the concept that air inside a container needs more force to be compressed from 2 to 3 bars than from 1 to 2.

[JoeAyalaM]

Originally Posted by PunsGalore

I think I'll go without - I don't tow or go offroad, and the steel suspension is plenty comfortable while still being sporty enough. Plus cheaper cost and better reliability down the line. Thanks all!

Good, I believe you won't be dissapointed, may be some buyer's remorse can set it, but that'll be it.

[JoeAyalaM]

Originally Posted by matowi

So, to stir up the topic even more, and to add value to the entertainment aspect of this thread, let me share an observation that my M60i X5 on the adaptive M Performance Professional suspension with 22 inch non-RFT wheels rides better than a 2021 7-series I just sold, which had executive drive system (air suspension on all 4 corners with active anti roll bars) and rode on 21 inch RFT wheels

Now, for full disclosure, the precise measurement instrument I applied to arrive at the conclusion mentioned above is my very own bottom. It’s an entire science department that deals with the question of “what it means that a car drives better”. But that question wasn’t asked by OP, so I’ll stay mute on it for the moment

Ooooh, X5 more comfy than 7 series! Is that because of a different suspension geometry? Or because of a longer travel height, or something else? Old vs new generation RFTs?

Can somebody imagine how much more comfy the X5 could be with the Air Suspension?

[matowi]

[Ludo2024]

Not sure i care much about all this science behind it but I come from 4 years of an X5 M50d with Sport seats and msport suspensions and 22” wheels. Hardly used the suspensions in their sport setting as they are far too hard especially in combo with the sport seats. After 500Km trips you really start feeling quite uncomfortable so it’s mainly custom sport mode with suspensions in their comfort setting. This time round I opted for the X5 M60i with Comfort seats and Air suspensions. Most of the time i want an Suv to be comfortable. Very few times do I need it to be a bit more sporty and that usually happens when on the Gerrman autobahn. I’m pretty sure the air suspensions in their lowered sport mode will be fine, if not better than the standard msport ones, even when travelling at 190km/h-200km/h.

[dhdd]

I have the 50e and I set my individual preferences to sport mode. Agree with other posters here that its a nice ride, firm enough but not floaty as normal setting. I can't stand the normal setting. I have other SUVs with air suspension and the X5 is just superior with the ride dynamics.

When I really want a sporty ride, I take my wagon with ohlins

[tooloud10]

Originally Posted by BlkGS

They have that reputation because they are less reliable. They leak, the lines leak, the compressors fail, ride height sensors fail... Steel springs basically don't fail. Maybe in some rust hell, but if your springs Have rusted to failure, the rest of the car.likely rusted away long ago.

Steel springs don't fail? They're a standard maintenance/wear item, unlike air suspension where there's no need to touch unless there's a problem.

Steel suspensions start 'failing' as soon as you leave the dealership.

Originally Posted by jad03060

A typical steel spring may not physically break very often, but they do not retain the same spring rate throughout their entire life while an air bag does…works until it fails. If you want simpler, don’t buy a BMW. With anything, the more complex it is, the more there is to break or wear out, and the cost to maintain goes up, but in routine maintenance and in replacement as things age and wear out

Exactly, and over 20 years of owning cars with air suspensions I've replaced one compressor and two air shocks, while every standard suspension needs to be replaced at 100k miles like clockwork. The fact that most people don't do this because the failure is slower and more subtle doesn't make them 'more reliable' than air suspensions.

I'm literally 'money ahead' to drive cars with air suspensions at this point because they're a 'potential' replacement instead of a 'scheduled' replacement item.

[Jen4BMW]

Originally Posted by BlkGS

But but but, the BMW sales person said the air suspension is the bestest, it rides better and is sportier and it's the best option! How could your butt o meter being feeling float that doesn't exist!?

I am not following your last post but I do get the condescension. Where did I say anything about being told AS is the best or to quote your words “bestest”.

How do I feel float that doesn’t exist…

Your point?

[jphcbpa]

Originally Posted by MotoWPK

To summarize the physics involved...

The pressure/volume relationship of a gas in an adiabatic process is:

P2/P1 = (V1/V2)^n

where P1 and V1 is the pressure and volume of the gas in the air spring at the static ride height, P2 and V2 the pressure and volume of the air spring deflected. n is the adiabatic gas constant which for air is 1.4.

Adiabatic is applicable here because the duration of the process, suspension deflection, is short enough to provide for minimal heat transfer of the gas to its surroundings.

Using this relationship with dimensions found for the X5's suspension and gas struts, the pressure ratio from the static condition at the normal ride height for various suspension deflections in compression is:

Compression
Deflection - mm Pressure deflected/pressure static
10.....................................1.08
20.....................................1.16
30.....................................1.26

The same calculation starting from the sport level ride height, 20 mm lower than the normal level ride height, is:

Compression
Deflection - mm Pressure deflected/pressure static
10.....................................1.26
20.....................................1.37
30.....................................1.50

Two things to observe here;
1) The greater pressure rise for the same suspension compression, therefore, a high spring rate, and,
2) The pressure ratio increases with the degree of compression resulting in a corresponding increasing force, or a variable spring rate.

To further clarify this last point, an increasing force with increasing deflection is not spring rate, spring rate being define as the change in force per unit deflection. So for the above examples, a deflection from 20mm to 30mm produces a greater pressure (force) increase than the change in deflection from 10mm to 20mm - a variable spring rate.

By comparison, the common coil spring of constant wire diameter, coil diameter and coil angle and pitch produces a force proportional to deflection; i.e. compress the spring 10% and the force increases 10%, compress the spring 20% and the force increases 20%, that is, a constant change in force per unit deflection - a constant spring rate.

Obligatory...

[starlights]

I haven't read through the entire thread but responding the OPs questions - I have air suspension and wouldn't have the X5 without it. For an SUV/SAV, the X5 with air suspension is stiff enough, especially when in (lower) sports mode without sacrificing luxury.

If I wanted any more sportiness I would have opted for an M Sedan. With the air suspension, I can have my cake and eat it too

Unless you plan to track your X5 - you should consider air suspension.

[dwwStL]

Originally Posted by Jen4BMW

I am not following your last post but I do get the condescension. Where did I say anything about being told AS is the best or to quote your words “bestest”.

How do I feel float that doesn’t exist…

Your point?

In forums like this -- and particularly car forums -- ignore can be your best friend and make your time here more enjoyable. I quickly put him on ignore and it has made all the difference.

[TurtleBoy]

Originally Posted by Jen4BMW

I am not following your last post but I do get the condescension. Where did I say anything about being told AS is the best or to quote your words “bestest”.

How do I feel float that doesn’t exist…

Your point?

Just ignore him. He was just lashing out and trying to make fun/be sarcastic in regards to the air suspension. He likely was a little embarrassed by his total misunderstanding of how the system works and trying, unsuccessfully, to save some face. I'm certain he was not saying anything against you or seriously questioning anything you said.

[FCX5]

Originally Posted by Dixie21

I've had both in both V8 and 6 cyl variants. I currently have M-Adaptive in my M60i and I enjoy it a lot more than I thought I would. Most of my commute to work is highway so I swore by air suspension. Yes, air is smoother on the highway, but the M-Adaptive isn't exactly choppy. With that being said, I do prefer air suspension because I it does stiffen up nicely in sport mode along with reducing the ride height. You can also lower the vehicle when parked which makes it look awesome. I completely understand how stupid that sounds, but it looks really good with spacers and lowered when parked haha

Doesn’t the adaptive M Pro have air suspension in the rear?

[FCX5]

Originally Posted by tooloud10

Can we dispel with the notion that air suspensions are somehow less reliable or wear out quicker than a standard steel suspension?

1) I’ve never had air suspension problems before 100k miles, at which point a regular suspension would have needed to be replaced anyway.

2) Air suspensions generally work the same over their whole lifetime—their performance usually doesn’t change unless something breaks.

3) For some reason the dealers really like to gouge on air suspension repairs. My kid’s old Land Rover made it to 140k miles before any problems, solved for $400 at my independent mechanic. The dealer would have wanted $4k.

Honestly, the air suspension option is the least scary thing about owning a car that’s otherwise this complicated.

Mine failed at 50K miles. Would have cost $4K, but was covered by extended warranty. Tech at Fairfax BMW told me it is quite common in X5 . You are lucky!

[BMPHIL]

Originally Posted by FCX5

Mine failed at 50K miles. Would have cost $4K, but was covered by extended warranty. Tech at Fairfax BMW told me it is quite common in X5 . You are lucky!

I would say it was you that was unlucky.

[FCX5]

Originally Posted by BMPHIL

I would say it was you that was unlucky.

Whatever…https://www.strutmasters.com/a/blog/...sion-problems#

[TurtleBoy]

Originally Posted by FCX5

Doesn’t the adaptive M Pro have air suspension in the rear?

No, air suspension and Adaptive M Pro are mutually exclusive.