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      02-15-2011, 07:13 PM   #1
stevebmw3
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BMW saves on rear suspension.

Where are thouse times when the car needed to have a aluminium suspension arms for lighter unsprung mass.

Now steel is enought.

Here more :
http://www.auto.cz/test-bmw-x3-xdriv...-trakare-54204
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      02-15-2011, 08:18 PM   #2
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Quote:
Originally Posted by stevebmw3 View Post
Where are thouse times when the car needed to have a aluminium suspension arms for lighter unsprung mass.

Now steel is enought.

Here more :
http://www.auto.cz/test-bmw-x3-xdriv...-trakare-54204
the rear is aluminum it's just painted to not rust .
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      02-16-2011, 01:35 AM   #3
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Quote:
Originally Posted by mike185 View Post
the rear is aluminum it's just painted to not rust .
Oh... Aluminum does not corrode...
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      02-16-2011, 12:18 PM   #4
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I'm pretty sure that's aluminum.
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      02-16-2011, 01:32 PM   #5
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Quote:
Originally Posted by mike185 View Post
the rear is aluminum it's just painted to not rust .
Sorry, No. The F25 chassis X3 uses high-strength stamped steel for the upper and lower control arms in the multi-link rear suspension and also uses a forged steel lower control arm in the front strut suspension. The front arm is plated and sure looks like aluminum, but it is not.

The rear upper/lower arms are thin stampings and are just painted black. Aluminum is lighter than a comparable amount of steel, but the currently available high-strength steels can often make a part stronger than an alloy component and still weigh less and take up much less room.
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      02-16-2011, 01:44 PM   #6
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Quote:
Originally Posted by Lotus7 View Post
Sorry, No. The F25 chassis X3 uses high-strength stamped steel for the upper and lower control arms in the multi-link rear suspension and also uses a forged steel lower control arm in the front strut suspension. The front arm is plated and sure looks like aluminum, but it is not.

The rear upper/lower arms are thin stampings and are just painted black. Aluminum is lighter than a comparable amount of steel, but the currently available high-strength steels can often make a part stronger than an alloy component and still weigh less and take up much less room.

Learn something new every day.
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      02-16-2011, 02:19 PM   #7
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Quote:
Originally Posted by Lotus7 View Post
Sorry, No. The F25 chassis X3 uses high-strength stamped steel for the upper and lower control arms in the multi-link rear suspension and also uses a forged steel lower control arm in the front strut suspension. The front arm is plated and sure looks like aluminum, but it is not.

The rear upper/lower arms are thin stampings and are just painted black. Aluminum is lighter than a comparable amount of steel, but the currently available high-strength steels can often make a part stronger than an alloy component and still weigh less and take up much less room.
I wonder if my local dealership would provide an answer like that if I asked the same question
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      02-16-2011, 04:09 PM   #8
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Quote:
Originally Posted by F25X3 View Post
LOL mine was amazed to find there was an acessories link on the bmw website.

Can someone please explain to me something thats making me a bit nervous? Ill explain. This sunday i test drove the X3 for the 2nd time and noticed something i never noticed in any other bmw ive driven. Since this thread is about suspension my issue might be related.
Anyways when on a straight line and after a quick turn and correction from the steering i could feel the front wheels turn and then the back turn. On previous bimmers ive driven - included my current X3 - when you turn, the cars turns as one feels like one if you understand what im saying. Anyway it felt weird and un-bmw like and didnt inspire much confidence to be honest. The car didnt have vdc or performance control btw. Thanks
Haven't experienced anything like that so far, but then I'm still patiently "being good" during the break-in period. Not to in any way question your vehicle set-up, but have you confirmed the correct tire pressures and the important F/R pressure differential. Don’t know the recommended pressures for the European “d” models, but for the N.A. models BMW insists on a 3 to 6 psi pressure bias in the rear tires depending on load and expected speeds.

When I received my car from the local dealer immediately after it went through an “extensive 3 hour check” (CA’s words, not mine) the tire pressures were all exactly equal and were 2 psi (cold) lower than the lowest pressure recommended for any driving condition.

Otherwise, the X3 is supposed to incorporate the late 3-Series “bump-steer” geometry, which as best as I can recall, is supposed to enhance stability if the rear end gets “loose”. With the much higher center of gravity and more body roll of the X3, you may be feeling the car’s suspension geometry trying to apply a little rear-wheel steer to compensate for the high roll.

Another factor is the relative lack of steering feedback in the X3. I have “pushed” our new F25 in some fast but tight corners, and noticed a slight tendency to (have to) make a second steering line correction just before exiting a tight 90deg. turn as the body roll flattens out. The lack of steering feedback means thet you don't do this automatically, and have to think about it. I’ve only been driving with the VDC set to “Normal” and hope the "Sport" or "Sport+" settings reduce this.

The other issue is the tires. I have the P7 All Season's tires which are certainly a compromise. On a previous car I owned (a 1999 Audi A4 Quattro Estate), going from the OEM All Seasons Dunlop’s to German Goodyear F1 DSG4’ s (set to optimal pressure by experimentation) made a dramatic difference. They almost totally eliminated initial understeer, reduced the steering angle at the limit, and made the car much easier to control in fast direction changes.

Last edited by Lotus7; 02-16-2011 at 04:15 PM..
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      02-16-2011, 04:22 PM   #9
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Quote:
Originally Posted by sfax View Post
I wonder if my local dealership would provide an answer like that if I asked the same question
If they're anything like my local dealership, you'd probably have to walk them under the car and identify the control arms for them.
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      02-16-2011, 05:14 PM   #10
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Originally Posted by F25X3 View Post
... I sure miss the days when ur bmw was just perfect to drive out of the box you know. NO need for vdc or variable steering or performance control
Know what you mean. My other car is a Lotus 7 replica: No power steering, no power brakes, coil-over suspension F&R, no VDC, no radio. Of course it corners perfectly flat (the geometric roll centers are below the center of gravity of the chassis) and the handling is almost perfectly intuitive. A quarter turn of the steering wheel is all you need for most sharp corners. Of course, if you ride over anything thicker than a small coin, you feel it through the suspension.
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      02-16-2011, 07:02 PM   #11
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Quote:
Originally Posted by Lotus7 View Post
Another factor is the relative lack of steering feedback in the X3. I have “pushed” our new F25 in some fast but tight corners, and noticed a slight tendency to (have to) make a second steering line correction just before exiting a tight 90deg. turn as the body roll flattens out. The lack of steering feedback means thet you don't do this automatically, and have to think about it. I’ve only been driving with the VDC set to “Normal” and hope the "Sport" or "Sport+" settings reduce this.
Based on my 3 test drives (2 28's and 1 35), I agree that the F25 has very poor steering feel, especially compared to BMW's with hydraulic power steering, but even compared to cars with Servotronic. Several reviewers have noted that as well.

Do you have DHP? The variable steering ratio might also explain what you experienced. A review I read somewhere on the web noted almost exactly the same thing and blamed it on variable steering.
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      02-16-2011, 07:19 PM   #12
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Steering changes dramatically between Normal and Sport.
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      02-16-2011, 07:51 PM   #13
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Quote:
Originally Posted by Lotus7 View Post
Quote:
Originally Posted by mike185 View Post
the rear is aluminum it's just painted to not rust .
Sorry, No. The F25 chassis X3 uses high-strength stamped steel for the upper and lower control arms in the multi-link rear suspension and also uses a forged steel lower control arm in the front strut suspension. The front arm is plated and sure looks like aluminum, but it is not.

The rear upper/lower arms are thin stampings and are just painted black. Aluminum is lighter than a comparable amount of steel, but the currently available high-strength steels can often make a part stronger than an alloy component and still weigh less and take up much less room.
thanks that's news to me I believe I read that it was aluminum and was painted to prevent corrosion , but I could be wrong thanks for correcting me
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      02-16-2011, 08:26 PM   #14
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Quote:
Originally Posted by mike185 View Post
thanks that's news to me I believe I read that it was aluminum and was painted to prevent corrosion , but I could be wrong thanks for correcting me
Just take a small magnet and reach around behind a rear wheel and touch the magnet to either of the exposed control arms. You will become a believer.

There have been SAE papers published on the rear suspension and the BMW "Insights" page states:

"Multi-link rear suspension keeps your BMW securely on track. Thanks to its intelligent lightweight construction, you can enjoy a high standard of agility and freedom from adverse forces or interference even on winding roads.

The lightweight steel construction of the multi-link rear suspension delivers remarkable weight savings and ensures the characteristic BMW near-perfect weight balance. The result is even greater agility and sporting performance. Despite its low weight, the axle offers superb rigidity.
Wheels are individually suspended and each is equipped with a number of guiding links. The precise design of the axle beam delivers excellent chassis support while enabling a system of dual elastic bearings for the rear-wheel drive and outstanding wheel guidance, all of which maximises passenger comfort."

Yep, whenever I consider buying a new car, "...freedom from adverse forces" is right at the top of my priorities list.
The above [BMW statement] clearly contains advertising copywriter drivel, but the basic idea comes through.

Although BMW does not specify the exact steel alloy they are using it’s probably ASTM A/1008A/M or A/1011/A/M, which are sheet metals suitable for “steering and suspension parts, door-intrusion beams and chassis members”. This material has a yield strength of up to 80,000 psi as compared to 36,000psi for conventional automotive steels. This allows thinner parts to be stronger, so provides a very real unsprung weight reduction. Production costs of these “high-tech” alloy steels is about 24% more than plain old A36 sheet metal.

Last edited by Lotus7; 02-17-2011 at 12:56 AM..
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      02-17-2011, 12:37 AM   #15
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Quote:
Originally Posted by F25X3 View Post
Might be just me but I ended up putting vdc in my order just in case.
Did you notice any difference (apart from the steering) between VDC in Normal and non-VDC? E.g. did it iron out the bumps in the road better?
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