Just Ordered '06 - Is Front Air Suspension the key to the 4.8 smoother ride?

z356 · #1 11-20-2005, 11:32 PM

I have done extensive search on this forum, Roadfly and Bimmerfest to figure out the reason most 4.8 owners claim their SAV rides better than a regular 4.4 X5 with Sport Suspension. After this analysis, I have concluded that the front air suspension (via option: Adjustable Ride Height) is the principal reason for their claim. Thus I have ordered my 4.4 with Sport Suspension, 19" style 132 wheels, Servotronic and Adjustable Ride Height. Basically duplicating the standard equipment on the 4.8, minus the bigger engine and 20" wheels. I hope to obtain the ride quality of the 4.8 without having to suffer the lower profile rubber on the 20" wheels. Is there a consensus among you that the front air suspension makes "the" difference and is the key to the perceived superior ride quality of the 4.8, even on 20 inch wheels & rubber? In case any of you is wondering why I just don't go with the 4.8, I just sold my '03 Audi RS6 because my wife complained often about the "stiff ride quality" on that vehicle. So I am trying to mitigate her "objections" via 19 inch wheels and air suspension on the X5, but still retain that special feeling of the sport suspension option which BMW seems to do so well and I have come to enjoy so much in my '04 745i (and standard on my Z8). So far, she has not complained about the suspensions on these two cars. Knock on wood. Your feedback will be greatly appreciated.

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Juanted · #2 11-20-2005, 11:37 PM

You'll soon find out that I have no useful feedback to give, and well, that will continue with this response. I just wanted to welcome you to the board and congratulate you on your purchase. Post some pics.

We do have a bunch of great, knowledgeable folks here, though. I am certain your question will be answered soon.

Juan

statdoc · #3 11-21-2005, 12:01 AM

I will be interested in your thoughts, to see if your hypothesis is correct.

z356 · #4 11-21-2005, 12:02 AM

Will post photos as soon as it arrives. Target date is Christmas. Color combination is Kalahari with Truffle Brown interior. Just about every option. MSRP is $65,750. My deal was $2,000 over invoice. Will only need to add a set of 18" wheels (probably replica 87s from Lakeshore) with Pirelli Scorpion Ice and Snows 255/55/18s. I am also considering the Dunlops M2s in 265/55/18, seen as an alternative X5 size at Tirerack website. Any feedback on these possible Winter tire choices would also be appreciated. Travel often between homes in Reno and Carmel (CA), so need good balance for snow, rain and dry road use on tires for winter months.

LVR · #5 11-21-2005, 03:24 AM

I have both an X5 with Sports suspension and a 4.8 with the air suspension. The 4.8 absorbs bumps and corners like a sports car with little body roll in comparison to the sports.

The first thing that is noticeable is that the 4.8 is lower with a wider stance.

As you said, the wheels are larger with lower profile tyres. Wheel size is important as this can affect the scrub radius (difference between the wheel centreline and the ball joint centre line) which relates to how positive the feedback is through the steering wheel. It also affects the cornering through the lateral forces absorbed by the tyre (sidewalls).

Track width resists the 'overturning inertia' when cornering, so it follows that a wider track will help the cornering.

Over bumps the initial shock transferred through the body is vastly lower, but I think this is partly due to the geometry of the suspension (eg damping rates) as much as the air suspension.

Around a corner the suspension is actively working different in my understanding. I think it has more to do with tyres, ride height (roll centre) spring settings, camber, caster and wider stance (Track width = lateral force) and then there is the electronic levelling side, which moves the roll centre during cornering by applying a 'jacking force' .... and is a whole world of confusion.......

The bump steer is vastly different. When you hit a bump mid corner in the sports (depending on the speed) it will require correction to your steering line whereas the 4.8 barely registers it. This is quite often due to the steering system geometry.

I think you would have to look into the specs of the steering, type of springs, geometry settings including camber (bump steer giveaway), caster, toe in/out settings to really answer your question.

That said, any upgrade of your suspension by the factory should require sympathetic settings to suit so it's all good.....

Cheers

z356 · #6 11-21-2005, 04:16 AM

Thanks for the post, LVR. Does your 4.4 Sport has Front Air Suspension? My research on the subject of 4.4 vs 4.8 reveals that there is some confusion on this point. Some have posted that a 4.8 and a 4.4 Sport with AHR (Adjustable Ride Height or front air suspension) have basically the same "sport" suspension. Is this true or not? Some, like you, are certain that they are totally different. Some have said that there is a ride height difference in 4.4 AHR vehicle vs a 4.4 non-AHR vehicle. That a 4.4 AHR is lower, per factory specs, than a non-AHR 4.4. Nothing to do with adjustable ride control function which returns the height to a factory setting at some speed; just that this default "normal" factory height setting is lower than the setting for a normal front coil spring & shock X5. Also that a 4.4 AHR sits a bit lower to the ground, like the 4.8. Is this true? Remember I am talking about a post-'04 4.4 Sport with AHR, not an earlier pre-'04 X5 with AHR. There must be many of you that have tackled this issue, I am sure. What is the secret to the 4.8 ride quality? Have you guys in this forum reached a consensus as to whether there is a real, quantifiable difference in the suspensions of a 4.8 and a current 4.4 Sport with AHR, other than the stock 20 inch wheels in the former? That is what I am trying to nail down. You might have a point in your technical explanation. I just want to see if other owners of 4.8 or 4.4 Sport {with front air suspension} in this forum agree, or not, with this theory. My hope is that, at this late date in the development of the E53 X5, there is a definite answer to my question based on the actual & collective experiences of our members in their understanding the fundamental suspension dynamics of their vehicles.

dan_fitz · #7 11-21-2005, 12:02 PM

I have always heard that the suspension setup of the 4.8 and the 4.4 Sport w/ AHR is the exactly the same, but that the 4.8 ride is a bit stiffer due to the 20" tires.

dan_fitz · #8 11-21-2005, 12:18 PM

I have always heard that the suspension setup of the 4.8 and the 4.4 Sport w/ AHR is the exactly the same, but that the 4.8 ride is a bit stiffer due to the 20" tires.

DinanX5 · #9 11-21-2005, 12:55 PM

I too have always read/heard that the 4.8 suspension is identicle to the 4.4 sport (with air front). But I've also heard that the air front makes for a more comfy ride, while the standard sport (w/o air) is stiffer, and a little more planted in hard corners...

z356 · #10 11-21-2005, 01:16 PM

Thank you, gentleman. It would be of interest if others could also comment on the following technical information on AHR provided by an X5 owner from Sweden, which appeared in the Roadfly forum several years back.
http://bimmer.roadfly.com/bmw/forums/e53/1090685-1.html
Clearly it states this option has a positive "sporty" visual benefit, since its lowered. Also that it rides better (enhanced ride comfort & doesn't rock on corners) because of its front air suspension, combined with the standard rear air suspension, offers the difference. According to the post, this came officially from BMW of Sweden. Is this gospel or are there many that doubt the engineering claims behind this supposedly official BMW technical report?

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