Carbon wheels for BMW

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BMW is only a year or two away from making the word ‘alloys’ obsolete in the car industry.

The German premium car-maker is planning a rollout of the collateral technologies it picked up when it reinvented carbon-fibre manufacture with the i3 and i8 eco-cars and the centerpiece is a set of ultra-light, fully carbon-fibre allo…, err, rims.

It is the brainchild of the marque’s weight-reduction guru, Franz Storkenmaier. After developing a new system of industrialising carbon-fibre for BMW’s i sub-brand, he has now been tasked with finding other uses for its patents.

Among the things his team has found are a full carbon-fibre steering wheel, a one-piece carbon-fibre propeller shaft for the X5 and a new carbon-plastic compound that is light and strong and made from i3 production waste and rims.

In fact, it isn’t just that BMW has developed new carbon-fibre rims, but it has also developed a carbon-fibre/alloy hybrid wheel, too, with alloy spokes and a carbon-fibre rim. And now it just has to convince European regulators that they’re strong enough to be safe on the streets.

“We save 25 percent in weight compared to a forged alloy wheel with the hybrid wheel and another 10 per cent if it’s completely carbon,” Mr Storkenmaier said.

“It’s the most important kind of weight because it’s unsprung mass and there are also rotating mass advantages.”

Given carbon-fibre has a reputation for being light, incredibly strong but not enthusiastic about bending, we asked if there concerns about wheels shattering or becoming damaged to the point where the cars were dangerous to drive.

“The carbon-fibre wheels are very damage resistant. They’re actually more damage resistant to kerb hits than standard alloy wheels because the damage polishes out really easily.

“You can scratch it when you park and it’s better to polish out than aluminium. You can have the metal finish to it with the alloy hybrid, but it’s technically a better solution to go all the way and have a full carbon-fibre wheel.”

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It’s a similar story with the carbon-fibre steering wheel. While cosmetic carbon-fibre on steering wheels has been a production-car reality since the early 2000s, they all have metallic skeletons. Not any more.

Though it’s still a little way off production (and, again, needs European Union approval), the new BMW steering wheel uses a carbon skeleton and a carbon frame. When asked if carbon was perhaps too stiff for safety, Mr Storkenmaier countered that the job of arresting the driver in a collision was done by the airbag.

“The protection for the carbon steering wheel is the airbag. If you physically hit the steering wheel, it will not deform and you’ve already lost. That’s the same with metallic steering wheels.”

But while those technologies were the coolest new carbon-fibre parts in the BMW works, they’re not the ones BMW is most excited about.

Instead, it has developed a carbon-plastic hybrid material called Secondary CFRP that is being positioned as a competitor for magnesium, aluminium and steel in light, semi-structural parts like seat frames and spare wheels for everything from MINI to Rolls-Royce.

“We have tried to use the leftover raw carbon-fibre from i3 and i8 production to make carbon-fibre parts, mixed with plastic. We chop up the leftover fibres and mix them all together, so it doesn’t matter where they come from or what their original job was supposed to be.

“After we cut them up, we mix them with plastic and this mix can be used in regular plastic-moulding machines, but it comes out stronger and lighter than any thermoplastic.

“We are the very first car-maker to use carbon-fibre on an industrial scale. Now we are able to use the leftover from the mainstream production on an industrial scale, too.”

To emphasise his point, BMW demonstrated a full, complex dashboard support structure made entirely out of one moulding from the new material.

“We have developed an instrument carrier (dash support structure) out of this material and it could replace the magnesium one at a weight saving of about 20 per cent. It’s even higher for seat frames because they’re typically made from heavier metals than magnesium.

“Carbon-fibre is an expensive material to work with, but if you are using production waste then it’s a different cost structure from working up raw carbon-fibre.

“It’s cheap, and that’s how we can position it as a competitor to magnesium.”


Words - Michael Taylor, www.carsales.com.au

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