I have assembled a racing bike weighing “x”, by using commonly sold components even if most of them come from abroad. Can I get the copyright or other forms of protection just on the weight?

The weight of the goods is a feature that cannot be considered for an industrial right, whether it is a patent or any other kind. Admitting this sort of protection would mean precluding anybody else manufacturing the same object with the identical weight, but using different components and therefore, this would constitute a regime of monopoly. To protect this type of invention you could register a patent for a model describing the manner and components used to make this bicycle having a certain weight “X”. As this is a finding lacking any inventive character, the result of which is just given by the assembling together of already existing parts, the offered protection is very minimal, so you could only prevent others making the same bicycle in the patented manner, but you could not prohibit someone else constructing the same bike by modifying at least one of its components. In any case, if the achieved weight were really very particular, it would probably be difficult for someone else to get the same result by making the bike in a different form; therefore the protection foreseen by the law might be sufficient.