Fitted onto a 80’s peugeot frame road bike (top) & closeup (bottom).
Designing any performance component often requires striking a balance between stiffness, strength and weight. Often for these applications we traditionally turn to high-grade metals such as steel, aluminium and titanium alloys which sit at the apex in terms of mechanical performance. The tradeoff with these materials is their high density, which makes them impractically heavy to use in solid form.
To combat this we combine these materials with a range of cross-sectional profiles: tubes and I-beams being classic examples. Different shapes provide different mechanical characteristics from bending to torsion so it is critical to consider the mechanical application in order to maximise structural efficiency.
Our vocabulary of such shapes has always been limited by our ability to manufacture them. New processes however are challenging these long standing limits, enabling us to now explore three dimensional architectures. This ability allows us to push objects and components even further in terms of not only their structural efficiency but also the mechanical behaviours they can create — Nature has always used architectural complexity in this manner to produce mechanical functionality beyond the limits of its material palette.
Designing a plastic handlebar is a challenge in terms of both strength and stiffness and we can utilise a material architecture to make the most of the material. In simple mechanical terms a handlebar is a cylindrical beam held at its centre experiencing cantilevered forces applied at the tips. The maximum stress experienced by the beam is at the point where the bar meets the stem.
Simulation of consecutive layers of laser profiles for two SLS handlebars based upon a standard tube profile (top) and an architectured design (bottom)
To combat this we employ an architecture that switches from tube to solid. Dimpling the surface of the skin adds further structural integrity as well as a better gripping surface for the rider. The thin wall section of the skin further away from the bar is reinforced by an over-constrained lattice structure in the core of the bar.
Carbon filled plastics use short fibers to boost their mechanical properties while retaining their ability to be formed through standard plastic manufacturing processes. The benefits are less pronounced as woven carbon fibre composites but such materials are capable of being almost an order of magnitude stiffer than the plain variety with little cost in terms of density. The handlebar is constructed from a carbon filled nylon approximately 3 times stiffer than off the shelf ABS. The architecture was developed and optimised based upon this material with care taken to take advantage of the anisotropic properties resulting from fibre orientation.
Carbon handlebar and titanium tube handlebar.
The final straight bar weights just under 150 g with a bulk density of 0.84 g / cm3. Measuring real world mechanical performance was done through a cantilevered beam test to simulate the typical loading the bar experiences in everyday use. In these tests the bar peaked at loads of 1.5kN before failing about 150 kilos being hung at the tip of the bar.
Cantilevered loading test on an carbon handlebar.
But performance in the real world is rarely about numbers alone. In the end the pressing question beyond mechanical capability is how does it feel under everyday conditions, from extreme forces to outdoor weather and in these occasions the only way to test this is first hand.
In everyday use.
I’ve ridden some 250 miles on this handlebar on London’s pothole-laden-freak-rain-soaked street. I’m happy to throw my full weight into this thing with little evidence of fatigue or wear so far. I’ll let you know how it fares at the 1000 mile mark.