Boas
Não sendo um leigo na matéria, mas curioso e até interessado em construir as minhas próprias rodas, tenho lido bastante sobre o assunto da construção de rodas, e daquilo que tenho lido alguns são factos consumados para a grande maioria e outros assuntos levam a grandes divergências de opiniões entre os construtores. Quanto ao numero de raios esse é um facto mais que consumado,pois é da opinião da maioria dos mais "conceituados" que é preferivel ter mais raios do que ter um aro de maior perfil, tanto mais que o que interessa é mesmo manter o menos peso possivél na periferia (principalmente no caso de quem quer construir umas rodas leves, e não aero).
Quanto aos cruzamentos dos raios, tudo depende do que se quer das rodas, o facto de serem radiais faz das rodas um pouco mais rigidas, mas também menos confortáveis sendo que muitos dizem que o grande beneficio é de reduzirem o peso das rodas (como os raios não cruzam são necessariamente mais curtos, logo mais leves).
Deixo aqui alguns tópicos de um site de um reputado construtor:
Spoke Count: Wheels with fewer spokes are generally more aerodynamic. They are also subjected to much higher spoke stress since fewer spokes are required to carry the same dynamic load. Generally higher spoke counts contribute to higher wheel strength and stability. For race wheels, you may want to consider fewer spokes, however there are few benefits to training on wheels with lower spoke counts and typically the result is broken spokes. Consider your body weight, intended wheel purpose, and riding style before deciding on the number of spokes. Also be sure to select rims and hubs with the same number of spoke holes.
Hub Weight: Of all the components on a wheel, the hub plays the smallest role on rotating inertia because it is located as close to the center of rotation as possible. This means that the weight of the hub is not as significant as the weight of other wheel components located further from the center of rotation (i.e., rim, nipples, tires, or tube). On bicycles with suspension, the weight of the hub contributes to unsprung mass -- these systems will always benefit from decreasing hub weight. On road bicycles, decreasing hub weight often affects ride quality and steering characteristics; however, these effects are usually small within a limited range of hub weights. Decreasing hub weight on a road bike will make your bike lighter, which can be an important factor for racing or climbing where every gram can help performance.
The ideal number of spoke crossings depends on a number of factors, but the most efficient power transfer occurs when the spoke leaves the hub at a tangential (90-degree) angle. The appropriate number of spoke crossings depends on the number of spokes on each flange. With 20 or 24 spokes, a 2x pattern is ideal; 32- and 36-spoked wheels are better suited to 3x. As the number of spoke crossings increases, the length of each spoke increases. Longer spokes are more flexible, which improves the ride quality, but also results in decreased radial stiffness.
Fonte: wheelbuilder.com
Delamadera, já agora aconselho-te a ires ver esta
tabela porque num dos sites que eu aprendi alguma coisa sobre rodas chama a atenção para o pormenor das tensões dos aros ZTR.