Although carbon-fibre forks have come and gone over the years in MotoGP, a new set of carbon suspension developed by BMW and ZF in Germany helped the M1000RR to victory at the recent Spa 24-hour race.
As far back as 1983 Honda created carbon forks as well as a carbon frame for the ultimate, and never-raced, version of the four-stroke NR500 GP bike.
Over the last few years, Öhlins carbon forks have become a mainstay in MotoGP since their debut in 2017, but using the tech in endurance racing puts it under a different sort of strain by requiring it to perform for thousands of miles at race pace for 24 hours. No carbon forks have been used under those conditions before.
As well as the obvious advantage of saving weight compared to conventional forks, the carbon versions allow a more subtle set of improvements thanks to the material’s ability to be tuned to change its rigidity.
BMW Motorrad Motorsport Director Marc Bongers said: “This technology allows us to shift the threshold at which body vibrations occur.” In other words, it’s a means to combat fork chatter.
“Handling is determined by everything that happens between the points of contact of the front and rear tyre,” he continued. “The fork is a key part of the overall package here, because it is important for how the rider feels when braking and cornering. However, this overall package also includes chassis and swingarm, for example.
“Then there are the practical requirements for the component in fine-tuning. We provided our input with all these various factors, and ZF implemented it with their technologies – and tailored the fork to our requirements.”
In detail, the carbon elements of the fork extend far beyond the visible carbon-fibre outer sleeves. In fact, the tubes that slide inside them are a carbon composite, albeit with a layer of metal glued to the outside for a low-friction finish.
Because carbon can be tailored to flex differently depending on how its fibres are laid, the forks have the scope to be more rigid in one direction than in another. For instance, they could be designed to withstand longitudinal bending forces under braking while flexing more when sideways forces are introduced, as they might be when you hit a mid-corner bump with the bike cranked over on its side.
Although there’s no word yet on production versions of the new forks, BMW have had a long association with carbon-fibre – as illustrated by the exotic, carbon-framed S1000RR HP4 Race of 2017 and use of carbon in cars, so don’t bet against something similar showing up on a future high-end road bike.
Rapid changes: As a race fork, the internals have been designed unlike road components, allowing fast spring changes in minutes to tweak the handling.
Fine-tune the flex: Flex, weight and rigidity can be altered by changing the thickness and layout of the carbon mat, allowing several variations to be made and tried at the track.
Composite inner: Although it can’t be seen, the inner tube is a made from a metal carbon fibre composite, combining the properties of metal and carbon to reduce its weight.
Full-carbon tube: The outer tube of the new ZF forks is entirely carbon fibre, giving the most visible clue to their different construction.
Low-friction lining: The visible metal fork leg is glued to the hybrid inner tube, giving a smooth surface where the inner and outer elements slide against each other.
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