CompositesWorld
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JUNE 2016 46 CompositesWorld FOCUS ON DESIGN bike quality?" Te short answer was simple: Fit, handling and engineering. But he could not fnd a bike with the ft, handling and engineering he desired. Tus, Rolo Bikes was launched in 2011. Rolo's mission is simply stated, but complex in execution: Design a bike frame that optimizes rider comfort and pedaling efciency, applying carbon fber in a way that maximizes material application while minimizing weight. Tis would require a holistic, back-to-basics design assessment, says Wais. "We started," he says, "by looking at the relationship between the three human contact points on a bike: Te saddle, handle bars and pedals." One data point emerged as criti- cally important in overall frame design: the stack/reach ratio. Te stack is the vertical distance from the bottom bracket (crankshaft) to the top of the head tube. Te reach is the horizontal distance from bottom bracket to the top of the head tube (see drawing, p. 45). If this ratio is low, the rider is more stretched out over the bike (less comfortable), but also in a better aerodynamic profle. If stack/reach ratio is high, the rider sits more upright (more comfortable), but in a less aerodynamic profle. A variable in this ratio is body type — leg, torso, arm length — but Rolo's research, says Wais, revealed that regardless of body type, most people have bodies that are, statistically, proportional. So, the question became, "What is the ideal stack/reach ratio?" Rolo's answer is 1.5:1. Tis number ofers the best balance of comfort and aerodynamics. Next, Rolo evaluated an apparently trivial design feature that actually has signifcant impact on bike performance. Called the trail (see drawing), it's the imaginary distance on the ground created by the angle between the head tube and an imaginary vertical line through the front hub. A long trail is more self-stabilizing, but makes wheel turning more difcult. A shorter trail tends to create wheel futter. So, what is the ideal trail? Rolo says 52 mm, which is relatively short. Says Wais, "We opted for a low-trail bike, which feels twitchy at frst, but as speed increases, handling gets much easier." With these data in mind, says Wais, Rolo developed its frst carbon fber monococque bike frame, designed in Dassault Systèmes' (Waltham, MA, US) SolidWorks. Te result, based on M55J UD and M46J twill epoxy/carbon fber prepreg (Toray Carbon Fibers Europe, Paris, France), hand-laid in a metallic mold with bladder core and cured in an autoclave, was estimated to weigh 830g. Making good even better Rolo and Wais, however, weren't done designing. Te lightest bikes in the world have frames of less than 700g, and Rolo had to be able to compete at that level. Read this article online | short.compositesworld.com/ClassChass Altair Engineering's Kate Fisher provided optimization services and says two frame components — the head tube and the bottom bracket (shown here) — received the most attention. Plies were added and rearranged to enhance stifness, but the weight added in the head tube and bottom bracket was more than ofset by the minimization of reinforcements in other areas. Source | Rolo Bikes