Is carbon fibre suitable for bikes?
BMW Motorrad is leading the charge for more carbon fibre on motorcycles with a patent for a carbon fibre swingarm and carbon fibre wheels, fairing and fenders for its S 1000 RR sports bike.
The latter are among their new M performance parts catalogue, but it shows their commitment to lightweight motorcycles.
But in this drive for lighter weight for both better performance and economy, are they sacrificing structural integrity and safety?
Carbon fibre is a material consisting of thin, strong crystalline filaments of carbon, used as a strengthening material, especially in resins and ceramics.
It has been around for many years with early development in cars by Toyota and BMW.
Performance motorcycles have long offered various carbon fibre accessories, but nothing really structural.
Today’s carbon fibre is a lot better produced and BMW has shown that it can even be used in the frame.
Many riders are still sceptical that it can withstand the unique physical punishment in a motorcycle.
Race engineer for Porsche and Supercars, Jeromy Moore, says that compared with ABS plastics, carbon is more brittle, but is lighter and stronger in that it takes a higher load until it fails.
“It can be used in combination with Kevlar which of course is used in bullet proof vests as it’s strong and impact resistant,” he says.
“There are also flexible resin systems out there now that allow movement under low loads and the parts return to original position.”
That seems to be what BMW Motorrad is doing with its swingarm which uses flex rather than a pivot.
Jeromy says Kevlar is not as stiff as carbon but still has higher stiffness-to-weight ratio than plastic.
As for how it stands up in a crash, Jeromy says it depends on the crash.
“Plastic will just deform and you may be able to repair it,” he says.
“A composite that has been deformed past its yield is throw away.
“It is more expensive and I think unless you are looking for the last tenths of a second around a track by shaving a few kilograms, on a road bike it’s just an expensive nicety.”
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