A step backwards?

[AusBmw]

New BMW 5 Series To Be Steel, No Aluminium

http://www.themotorreport.com.au/wp-content/uploads/2008/writer/c6209c7d97f0_A5A4/bmw_5_2010_render_01_thumb.jpg

At first glance, the news that the next BMW 5 Series will feature an all-steel chassis instead of a part-aluminium construction – such as in the current model – seems like a step backwards.

And perhaps technologically it is. It won’t be lost though. There’s no doubt that BMW will have learned a lot about aluminium construction technologies that we will see again in future models.
http://www.themotorreport.com.au/wp-content/uploads/2008/writer/c6209c7d97f0_A5A4/bmw_5series_aluminiumfrontend_thumb.jpg

Above: The aluminium front-end of the current BMW 5 Series.

Specifically it is the cost and complexity of manufacture for the current model’s aluminium space-frame front end – attached to the otherwise steel body – that BMW has found too great to bear.

Originally devised to provide improved weight distribution and cut weight, the process proved to be too costly. According to a BMW insider, it was “an expensive solution and troubling to perfect in large-scale production”.

For the same reasons, BMW dropped the same approach to the new 7 Series

http://www.themotorreport.com.au/23207/new-bmw-5-series-to-be-steel-no-aluminium/


:wow:

One wonders if this is just a cutback based on current economic downturn, but the cars chassis would have been signed off on before all this took hold yes?

[InsidiousSpeed]

I thought the E60 5 series and E66 7 series were all steel. Only our 6 series was all aluminium chassis, part aluminium and plastic panels.

Whatever.

Just give us a 600bhp / 450kW and 700Nm torque plus M5/M6 with all the right handling next time and I doubt we'll care much what's holding the car together.

[ZCP///M3]

Wouldn't an all-steel chasis perform worse in an impact because it doesn't have the crinkling capabilites as aluminium? Plus the car is going to be heavy.

[Richard in NC]

The E39 was all steel but with aluminum sub frames for the suspension. It had great crash ratings. Its the design that allows it to "crinkle".
The e60/61 & e63/64 have the aluminum front end. It is also good in frontal crashes but maybe not quite as good. See the pics for e39 and e61 frontal crash examples. IIRC, both were 40mph crashes where they walked away. The E39 M5 was going 40+ MPH and tboned an SUV running a redlight at 60+. The SUV was hit hard enough to tip over. Its driver was rushed to the ER while the M5 driver had no injuries other than soreness and airbag burns.

Not only is production more complex and costly with the aluminum front but crash repair is significantly more complex/costly. It takes specialized equipement to repair it and few independant shops can do it. Many BMW colision centers can't either. I bet that's the bigger reason why its dropped.

PS: The e63/64 adds the plastic trunk and fenders for weight savings to the steel/aluminum chassis. The M6 then adds several carbon fiber pieces (roof, bumper supports, plus a few more pieces) to save a few more pounds.

[bdaw]

Wouldn't an all-steel chasis perform worse in an impact because it doesn't have the crinkling capabilites as aluminium? Plus the car is going to be heavy.

They can engineer crash zones in the steel to give way during an impact.

[AusBmw]

I wasn't worried about safety, more chassis performance and balance, given most car makers don't like to go backwards.

[bdaw]

I wasn't worried about safety, more chassis performance and balance, given most car makers don't like to go backwards.

Except Porsche with the 928...although they never were rear wheel drive front engine....and it wasn't going backwards when they went back to the 911.

[InsidiousSpeed]

I wasn't worried about safety, more chassis performance and balance, given most car makers don't like to go backwards.

I think BMW will always design a top class chassis for the car, whatever the material used, coupled with electronics, which BMW is never short of. When I attended one of the Drive Days, an instructor said it's very difficult to bond iron with aluminium, or aluminium with aluminium (I can't recall exactly), and BMW had to use some super-super-glue to do that.

So, they should just make the car out of one top-end material but then you run into cost constraints and price segment limit of the car they build. It's alright to make a MacLaren SLR out of 100% carbon fibre, but for a run around family 5 series sedan, with Honda and Lexus offering more of everything, you can imagine the tough business they're all in.

[boxboss]

I think BMW will always design a top class chassis for the car, whatever the material used, coupled with electronics, which BMW is never short of. When I attended one of the Drive Days, an instructor said it's very difficult to bond iron with aluminium, or aluminium with aluminium (I can't recall exactly), and BMW had to use some super-super-glue to do that.
Basically hard to join any two different metals. "Galvanic" corrosion http://en.wikipedia.org/wiki/Galvanic_corrosion occurs and degrades the metals and the bond. I know the 6er's body panels were glued to the frame, but I don't think the steel/aluminum chassis bonds were super-duper glued.

There's nothing wrong with an all steel frame, except for the weight. In BMW's case, this really hurts the weight distribution and makes an already overweight GT even heavier. They will overcome this problem, though...maybe chrome-moly alloy like is used in upper end bicycle frames?

[Richard in NC]

Basically hard to join any two different metals. "Galvanic" corrosion http://en.wikipedia.org/wiki/Galvanic_corrosion occurs and degrades the metals and the bond. I know the 6er's body panels were glued to the frame, but I don't think the steel/aluminum chassis bonds were super-duper glued.

Yep. I found the E60 press release from 2003. I had to copy as image since I couldn't copy the text directly.

http://bimmerdrivers.com/forum/attachment.php?attachmentid=1986&stc=1&d=1236911868
http://bimmerdrivers.com/forum/attachment.php?attachmentid=1987&stc=1&d=1236911868

[boxboss]

Great info Richard. At least they used some rivets along with the super glue.

[abe]

Not only is production more complex and costly with the aluminum front but crash repair is significantly more complex/costly. It takes specialized equipement to repair it and few independant shops can do it. Many BMW colision centers can't either. I bet that's the bigger reason why its dropped.

That's exactly what I thought of when it was mentioned. When it comes to repairs, steel is a much easier metal to work with, mostly because most cars are made out of steel. Contamination into aluminum shops ruins the work. They have to have their own sets of tools that cannot be used on steel parts. Read about it in Car and Driver a few months back when someone wrecked an Audi S6. With all that aluminum they had to find a shop to handle it and there was only one in MI (I think).

BTW, like the look of the new 5 series (if that's the way it's going to look). Like the ridges on the hood.

OK, I'll go back to the Audi forum. Now where is that? :dunno: :mrgreen:

[chuck92103]

Glad to see the Grav front end go. The aluminum front end on a 5/6 has caused many BMWs to be totaled when in very minor collisions.

I think cars crumple a little too much now.

My friend's E55 AMG was totalled last week when he rear ended another car at low speed. The air bags did not even deploy yet the car was totalled and his front end is not aluminum. :shake:

In an effort to do things like Grav front ends, BMW adds significant cost to vehicles that the average cross shopper would not even recognize or appreciate.

My friend ended up replacing his totalled E55 with a G37 sedan after comparing it to a 5 series. He loved the 5 but did not see a $25k difference in price. I think his way of thinking is common for shoppers and BMW loses a lot of sales because of it. He understood the 5 is best compared to a Infinti M45, but even the M he thought was overpriced. I suspect the economy and not spending an excessive amount on a car is driving a lot of consumers now.