BMW i3 Successor – Steel Instead Of Carbon Fiber?

SEP 19 2014 BY STAFF 38



BMW Carbon Fiber

BMW Carbon Fiber

The BMW i3 has yet to have its one year birthday and reports on the next generation are starting to pop-up. With an investment of billions of dollars in the mass-production of i3 and a carbon fiber, the expectations are that future models will continue down the same path of lightweight construction.

But according to Herbert Eichelkraut, a manager of the German steel giant ThyssenKrupp, the strong metal might make a return in BMW cars. Eichelkraut says that BMW and ThyssenKrupp negotiate to build, in the next generation i3, “an important component of steel.” He has denied to specifiy which one.

*Editor’s Note: This post appears on BMWBLOG.  Check it out here.

It is clear that the carbon fiber materials are here to stay for the i sub-brand and will play a major role in other production cars as well. It is equally certain that some vehicle components have to be made of aluminum and other lightweight materials, mostly for safety crash reasons.

The fact that high-strength steel can be an interesting alternative to aluminum case is no longer a secret. Thanks to new molding techniques, companies like ThyssenKrupp can make very light steel components, which can be “as heavy” as similar aluminum parts but much more stable.

One component of the i3 that might benefit from the high-strength steel is Life Drive Module which is now made of aluminum.

If BMW keeps the 7 year production cycle, then the next BMW i3 won’t be out before 2020.

Source: WSJ via Bimmertoday

Categories: BMW


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38 Comments on "BMW i3 Successor – Steel Instead Of Carbon Fiber?"

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Perhaps the article can be modified to state that BMW’s materials are not “carbon fiber materials”, but plastic, reinforced by a veneer of carbon fiber. I hate how I have to police this nearly every single day…( sigh ). If I hear one more person say the i3/i8 is “made of carbon fiber”, I’ll scream – literally. That detail aside, steel manufacturers are not going to sit idly by and lose all their auto industry money by doing nothing as aluminum and carbon-type componentry gains ground. Light steel is an innovative and less expensive solution for many body parts and components, and surely will take their rightful place in the mix. The big engineering vs. accounting dep. debate will still be, “what material is best used where?” Surely, new lightweight steel will be in the mix as well as aluminum used in hoods, doors, suspension arms, etc.. The entire industry is watching the Ford F-150 experiment, and if aluminum turns out to be cost-effective in the short term – it no doubt will become mainstream in vehicles with MSRPs in the $30,000-and-above category. Gas mileage mandates are out there – manufacturers and suppliers will do this dance for years to… Read more »

You’re wasting your time with that policing.

That’s how carbon fiber is always used in the automotive industry. It’s useless by itself, and you need the polymer mixed in.

Moreover, you will always maximize the stiffness and strength of a part by putting all the carbon fiber as close to the outside as possible, i.e as a veneer.

Regarding the rest of your statement, aluminum alloys will always be much better than an equal weight of steel (even HSS) for panels/plates. It’s low density means that Al twice as thick as steel will be lighter, and 2x thickness increases bending resistance (second moment of area) by 8x, all else being equal. HSS can’t make up such a difference through yield strength and young’s modulus.

For other parts, like the frame, steel is very much game.

I contest your assertion. CFRP is different than standard carbon fiber construction in the auto industry or any other industry. Boeing is using carbon fiber for wings and fuselage sections on 787s and other retrofitted existing designs. This is carbon fiber, layered, glued and autoclaved on other sheets of carbon fiber mat. This is not a plastic mold with one sheet of carbon fiber glued on either side. Big difference. Racing cars and exotic supercars that use large amounts of carbon fiber use laminated sheets, not a single sheet of cf glued to a center of molded plastic. Glad to be able to educate you on the facts. If you want to go into the details of each material and it’s advantage as to other materials – you’d have to write a book or thick manual. You can’t broad-brush the whole issue into such simplistic terms. Each material has pros/cons for a myriad of applications. Suspension parts don’t posess the same requirements of body panels, and a roof panel doesn’t require the same things as say, a hood or hatch door. There are skins and supports and all sorts of detail you gloss over. If you really want to debate,… Read more »

Yes . . . it is different. So what? It does the job fine and I suspect it is a little cheaper than conventional Carbon fiber & resin material.

Precisely. It’s cheaper for BMW to build an i3 out of CFRP rather than carbon fiber, even after all the R&D, special tools, jigs, computer programs and repair tools they had to develop to get the end result! Cheaper than using layered carbon fiber, which is prohibitively expensive and not repicable to their high-profit ICE cars and SUVs of which they make hundreds of thousands each year.

The savings is not passed to you, the consumer, however – it makes i3 lighter which means it needs less battery pack to achieve 80 miles of EV range. So then we have to ask ourselves: “Why do I have to pay $50,000 for LEAF range?!”. Added benefits for BMW is that 8/10 publications and websites tend to say “i3’s are constructed of carbon fiber”, which, as you know, is untrue.

Smart for BMW. Not so smart for the consumer.

* Correction – “replicable”, as in – “replicable” in their high-profit, conventional ICE cars and SUVs of which they make hundreds of thousands per year.

Remember at i3’s North American introduction, when BMW officials stated the CFRP process was not specifically invented for the “i” Series – but to be gradually implemented into their existing line of cars and SUVs to reduce weight and increase MPG.

It appears BMW has banked more on CFRP than they have the advancement of lithium batteries for cost reductions of scale.

Not everyone needs to be involved in researching fundamental battery chemistry. Tesla haven’t too any great degree, at any rate for their present generation. What they do is assemble Panasonic’s batteries in a very clever way, the chemistry is not there. It looks as though Nissan is giving up on trying to compete with LG Chem, and is going to use their batteries, whilst VW’s policy was always to use the best chemistry available, and they use Panasonics, and in future it seems, LG Chem. BMW can do the same, rather than trying to compete with the couple of major players still standing in the car battery business. IMO BMW have positioned themselves very well. They can gradually expand their use of CFRP across many vehicles in their range, giving them a weight advantage. The i3 in my view was not only built with its present generation battery in mind, but the next, which is likely to give then a proper AER without the rather half-hearted RE which has plainly been designed as a stop gap until better batteries are available. BMW by not putting resources into a losing battle with the battery specialists have been able to deploy them… Read more »

Well said Davemart.

Wherever carbon fibre is used as a structural material it is CFRP even in the wings of Boeing aircraft. Carbon fiber without plastic has no structural properties. I really don’t get the point you are trying to make.

What is the frame of the i3 made out of? Certainly not CFRP, right? I assume today it is either steel or maybe aluminum. So maybe he’s talking about using lightweight steel for the frame? No reason you couldn’t do that plus also keep CFRP for the body panels. In fact, if that lowers the cost without adding too much weight, why not?

The frame is made from dry, carbon non-crimp fabric preforms that are resin transfer molded. Basically carbon fiber composite or CFRP as some refer to it as. The body panels are plastic with no carbon fiber at all. Most other vital components are aluminum.

Thanks for the clarification, Eric! I had no idea that the frame itself was CFRP.

That clarification is wrong. The “frame” is aluminum. The “life module” or body, is CFRP, which is basically a molded plastic piece with a sheet of carbon fiber glued to each side. Go to YouTube and watch the robots putting those pieces together.

Outside door panels, etc. are plastic.

Ugh…The frame is both the aluminum Drive Module and the carbon fiber Life Module. Both need to be present to offer structural integrity. Essentially both components are the “frame.” Frames don’t really exists these days. It’s all sub assemblies that rely on other sub assemblies.

I tend to agree with Warren’s observation – below.

There’s been all sorts of promo-speak invented for “life modules” or “safety cages” and all over the years. I once worked for Volvo, and we know that in spite of all the safety-speak, a frame is still a frame, a platform, a platform, and for this BMW i3, exploded drawings and graphics fully reveal that the aluminum substructure is what battery pack, “life module” and most all other components bolt to.

* “unibody” i3 is not.


The aluminum “Drive Module” is essentially the frame. The carbon reinforced plastic “Life Module” adds some stiffness when bolted on, but I would guess that aluminum box is pretty rigid on it’s own.

True…though I thought Brian’s comment on frame material was more or less linked to structural integrity. The Drive Module itself affords little occupant protection. Cars don’t have frames these days. Ugh…not gonna be able to explain this one how I’d like to. Both the Drive and Life modules should be considered the “frame” of the vehicle.

Yeah, I know. The term is semi-monocoque.

“An intermediate to full monocoque construction was the ‘semi-monocoque’ used by the Volkswagen Beetle and Citroen 2CV.”

My dad’s Ramblers were full monocoque. I remember his friends saying, “If it was any good GM and Ford would have it!” 🙂

I think this ( full-on monocoque ) is where the term “unibody” derived from.

Some vehicles referred to as: unibody are not full-on unibody structures. Others, as some racecars have been – are more or less full monocoque structures.

I’m not an engineer, so I can stand corrected. But I feel I’m more accurate than not on i3. It’s separate components, yes – but as Warren observed even from the photo above his post – the aluminum underpinnings of i3 pretty much support and provides enough rigidity to keep the entire structure solid without undue torsion. True, the passenger compartment and outside bodywork needs additional stiffening elements designed into it, but they are not the main
platform that supports the mechanical elements of the entire car.

I would say in the skateboard configurations of cars like Model S, the battery pack enclosure is a literal representation of a “frame” for those vehicles, since suspension and body are bolted directly onto it.

I, for one, am finding this a very informative discussion. I’m learning all sorts of fascinating things about this car. It sounds like it’s not as simply as my question assumed it was.

James – I will absolutely take your suggestion and track down some videos.

The problem is the benefits of the mass reduction are wildly exceeded by the costs. Bad choice. What’s surprising is that BMW would admit it and move on.

From the discussion it is clear that the steel makers are trying to win the business back from aluminium.

They are going to be assisted in this by improvements to the steel that they can make.
The aluminium producers will fight back though, and the CFRP stays.

So there does not seem to me to be any question of BMW backtracking, just a news story about their suppliers competing for their business.

You all might have missed i3’s North American introduction, where BMW officials plainly stated CFRP was not solely developed for the electric “i” program, but as a solution to Co2 and MPG mandates all over Europe and the world – enabling BMW to gradually adapt CFRP components throughout their ICE model lineup.

So as I’ve said before, it seems BMW has put more weight into CFRP than the advancement of lithium battery energy density to reduce costs by economies of scale.

See above.
BMW can just use Panasonic and LG Chem batteries, and don’t need and have no competitive advantage in trying to build them themselves.

BMW recently went from one shift to three at their carbon fiber plant. I don’t think they did that because they are backing away from CFRP.

All automakers are undertaking serious mass reduction programs. Some are visible, others not yet. But none are going to get to 2025 cafe standards of 54.5 mpg by the status quo.

Kudos to BMW for having the brass to do something truly innovative that is meaningful. Dropping 1,200 pounds off the i3 is no small feat. The fuel efficiency gains are real, and move the marker forward.

Everyone else except for Tesla is now playing catch-up.

We may, indeed, see 2nd generation i3 ( if there is one ) be more like it’s Mercedes B Class Electric Drive rival that vice-versa. The different types of high strength steels that are either here or coming soon make a good case against aluminum, composites and plastics.

Like there is no one-fuel answer to all of society’s energy needs, there is neither one material that stands out as above all others for the majority of automotive uses. Cost is the biggest concern and it’s interesting to see the various solutions that rise to the top after experimentation and implementation.

We’ll see magnesium, thermoplastics, new light steel materials with advanced alloys, along with lots of aluminum and I’m sure, some CFRP plastic/cf in the future. Look to Renault’s new Eoplan PHEV concept for a glimpse into the complex future of materials
utilization on an automobile.

I know you guys hate links, but this is a good one:

RENAULT EOPLAN PHEV materials graphic –

Its true enough that materials are increasingly mix and match.

BMW have just invested very large sums though to set up CFRP production, and it seems wildly improbable to me that they are just going to throw that away.

In addition steel and aluminium are usually the ones which swap about.

There seems absolutely no reason to think that the steel is to replace the CFRP.

Steel is cheaper in cars that don’t take advantage of its stiffness. If BMW wants both light and stiff sports cars, there are better targets than the I3. I3 gave them a chance to start small. It’s EPA numbers would stand apart, if made with lead.

…cars that take advantage of CFRP’s stiffness, that is.

CO2 from production and recycling will soon be a big part of the equation. I will be fascinated to see how the various materials stack up

This is the down side of all that mixed materials.
How do you recycle them when it’s over?
More type, make more recycling headache and I’m not sure of any environment benefit on the full life cycle.

Why do we keep having this ridiculous argument. As if the fact that the i3 is the lightest AND quickest BEV in its class isn’t enough? Put a bigger battery and make the car heavier. Like the 1000lb heavier B class. Get one of the lowest mpge ratings and you will please James! And you think they actually did this just to save money on batteries? Believe me, There would have been much easier ways to do it than investing in SGL.

The B Class is a much bigger quieter 5 passenger car with 4 full size doors. And it has about 5 more miles of range than the i3 BEV.

i3 is four passenger car with half-sized rear hinged doors.

Very few moving parts, panels that don’t rust, change the batteries every 10 years and the car could last forever. No wonder BMW is going back to steel.

Sometimes it is counter intuitive but testing the opposite is often interesting.
Here it goes for a super heavy EV:
Lead battery
Tungsten body
Cristal windows
Silicone tires
(EV range 1 mile.)

What is that revealing?
Well not much on the body since Aluminum and CFRP are already detected, the same for the Lithium battery, but the windows are obviously not optimized by still being glass, they should go to the lighter polycarbonate and the tires should move to polyurethane. Glass and rubber tires filled with zinc oxide and fillers are obviously not lightweight.

On the body there still is room for some other materials like Yttrium steel and foam materials, like Aluminum foam or also Yttrium steel foam.